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1 | \input texinfo.tex @c -*- texinfo -*- |
2 | @c %**start of header | |
3 | @setfilename bashref.info | |
4 | @settitle Bash Reference Manual | |
5 | @c %**end of header | |
6 | ||
ccc6cda3 | 7 | @setchapternewpage odd |
ccc6cda3 | 8 | |
b80f6443 | 9 | @include version.texi |
e8ce775d | 10 | |
b80f6443 | 11 | @copying |
ccc6cda3 | 12 | This text is a brief description of the features that are present in |
b80f6443 | 13 | the Bash shell (version @value{VERSION}, @value{UPDATED}). |
ccc6cda3 JA |
14 | |
15 | This is Edition @value{EDITION}, last updated @value{UPDATED}, | |
16 | of @cite{The GNU Bash Reference Manual}, | |
17 | for @code{Bash}, Version @value{VERSION}. | |
18 | ||
95732b49 | 19 | Copyright @copyright{} 1988-2005 Free Software Foundation, Inc. |
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20 | |
21 | Permission is granted to make and distribute verbatim copies of | |
22 | this manual provided the copyright notice and this permission notice | |
23 | are preserved on all copies. | |
24 | ||
b80f6443 JA |
25 | @quotation |
26 | Permission is granted to copy, distribute and/or modify this document | |
0628567a | 27 | under the terms of the GNU Free Documentation License, Version 1.2 or |
b80f6443 JA |
28 | any later version published by the Free Software Foundation; with no |
29 | Invariant Sections, with the Front-Cover texts being ``A GNU Manual,'' | |
30 | and with the Back-Cover Texts as in (a) below. A copy of the license is | |
31 | included in the section entitled ``GNU Free Documentation License.'' | |
32 | ||
33 | (a) The FSF's Back-Cover Text is: ``You have freedom to copy and modify | |
34 | this GNU Manual, like GNU software. Copies published by the Free | |
35 | Software Foundation raise funds for GNU development.'' | |
36 | @end quotation | |
37 | @end copying | |
38 | ||
39 | @defcodeindex bt | |
40 | @defcodeindex rw | |
41 | @set BashFeatures | |
42 | ||
43 | @dircategory Basics | |
44 | @direntry | |
45 | * Bash: (bash). The GNU Bourne-Again SHell. | |
46 | @end direntry | |
47 | ||
48 | @finalout | |
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49 | |
50 | @titlepage | |
51 | @title Bash Reference Manual | |
52 | @subtitle Reference Documentation for Bash | |
b72432fd | 53 | @subtitle Edition @value{EDITION}, for @code{Bash} Version @value{VERSION}. |
b80f6443 | 54 | @subtitle @value{UPDATED-MONTH} |
ccc6cda3 JA |
55 | @author Chet Ramey, Case Western Reserve University |
56 | @author Brian Fox, Free Software Foundation | |
b80f6443 | 57 | |
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58 | @page |
59 | @vskip 0pt plus 1filll | |
b80f6443 | 60 | @insertcopying |
ccc6cda3 | 61 | |
b80f6443 JA |
62 | @sp 1 |
63 | Published by the Free Software Foundation @* | |
64 | 59 Temple Place, Suite 330, @* | |
65 | Boston, MA 02111-1307 @* | |
66 | USA @* | |
ccc6cda3 | 67 | |
ccc6cda3 JA |
68 | @end titlepage |
69 | ||
b80f6443 JA |
70 | @contents |
71 | ||
72 | @ifnottex | |
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73 | @node Top, Introduction, (dir), (dir) |
74 | @top Bash Features | |
ccc6cda3 | 75 | |
ccc6cda3 | 76 | This text is a brief description of the features that are present in |
0628567a | 77 | the Bash shell (version @value{VERSION}, @value{UPDATED}). |
ccc6cda3 JA |
78 | |
79 | This is Edition @value{EDITION}, last updated @value{UPDATED}, | |
80 | of @cite{The GNU Bash Reference Manual}, | |
81 | for @code{Bash}, Version @value{VERSION}. | |
82 | ||
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83 | Bash contains features that appear in other popular shells, and some |
84 | features that only appear in Bash. Some of the shells that Bash has | |
85 | borrowed concepts from are the Bourne Shell (@file{sh}), the Korn Shell | |
86 | (@file{ksh}), and the C-shell (@file{csh} and its successor, | |
87 | @file{tcsh}). The following menu breaks the features up into | |
88 | categories based upon which one of these other shells inspired the | |
89 | feature. | |
90 | ||
91 | This manual is meant as a brief introduction to features found in | |
92 | Bash. The Bash manual page should be used as the definitive | |
93 | reference on shell behavior. | |
94 | ||
95 | @menu | |
96 | * Introduction:: An introduction to the shell. | |
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97 | * Definitions:: Some definitions used in the rest of this |
98 | manual. | |
ccc6cda3 | 99 | * Basic Shell Features:: The shell "building blocks". |
bb70624e | 100 | * Shell Builtin Commands:: Commands that are a part of the shell. |
bb70624e | 101 | * Shell Variables:: Variables used or set by Bash. |
ccc6cda3 | 102 | * Bash Features:: Features found only in Bash. |
95732b49 JA |
103 | * Job Control:: What job control is and how Bash allows you |
104 | to use it. | |
105 | * Using History Interactively:: Command History Expansion | |
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106 | * Command Line Editing:: Chapter describing the command line |
107 | editing features. | |
ccc6cda3 | 108 | * Installing Bash:: How to build and install Bash on your system. |
ccc6cda3 | 109 | * Reporting Bugs:: How to report bugs in Bash. |
bb70624e JA |
110 | * Major Differences From The Bourne Shell:: A terse list of the differences |
111 | between Bash and historical | |
112 | versions of /bin/sh. | |
b80f6443 | 113 | * Copying This Manual:: Copying this manual. |
ccc6cda3 | 114 | * Builtin Index:: Index of Bash builtin commands. |
ccc6cda3 | 115 | * Reserved Word Index:: Index of Bash reserved words. |
ccc6cda3 JA |
116 | * Variable Index:: Quick reference helps you find the |
117 | variable you want. | |
ccc6cda3 | 118 | * Function Index:: Index of bindable Readline functions. |
ccc6cda3 JA |
119 | * Concept Index:: General index for concepts described in |
120 | this manual. | |
121 | @end menu | |
b80f6443 | 122 | @end ifnottex |
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123 | |
124 | @node Introduction | |
125 | @chapter Introduction | |
126 | @menu | |
127 | * What is Bash?:: A short description of Bash. | |
ccc6cda3 JA |
128 | * What is a shell?:: A brief introduction to shells. |
129 | @end menu | |
130 | ||
131 | @node What is Bash? | |
132 | @section What is Bash? | |
133 | ||
134 | Bash is the shell, or command language interpreter, | |
bb70624e | 135 | for the @sc{gnu} operating system. |
ccc6cda3 | 136 | The name is an acronym for the @samp{Bourne-Again SHell}, |
bb70624e | 137 | a pun on Stephen Bourne, the author of the direct ancestor of |
b80f6443 | 138 | the current Unix shell @code{sh}, |
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139 | which appeared in the Seventh Edition Bell Labs Research version |
140 | of Unix. | |
141 | ||
bb70624e | 142 | Bash is largely compatible with @code{sh} and incorporates useful |
ccc6cda3 | 143 | features from the Korn shell @code{ksh} and the C shell @code{csh}. |
bb70624e | 144 | It is intended to be a conformant implementation of the @sc{ieee} |
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145 | @sc{posix} Shell and Tools portion of the @sc{ieee} @sc{posix} |
146 | specification (@sc{ieee} Standard 1003.1). | |
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147 | It offers functional improvements over @code{sh} for both interactive and |
148 | programming use. | |
ccc6cda3 | 149 | |
bb70624e JA |
150 | While the @sc{gnu} operating system provides other shells, including |
151 | a version of @code{csh}, Bash is the default shell. | |
152 | Like other @sc{gnu} software, Bash is quite portable. It currently runs | |
ccc6cda3 | 153 | on nearly every version of Unix and a few other operating systems @minus{} |
bb70624e | 154 | independently-supported ports exist for @sc{ms-dos}, @sc{os/2}, |
b80f6443 | 155 | and Windows platforms. |
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156 | |
157 | @node What is a shell? | |
158 | @section What is a shell? | |
159 | ||
160 | At its base, a shell is simply a macro processor that executes | |
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161 | commands. The term macro processor means functionality where text |
162 | and symbols are expanded to create larger expressions. | |
163 | ||
164 | A Unix shell is both a command interpreter and a programming | |
165 | language. As a command interpreter, the shell provides the user | |
166 | interface to the rich set of @sc{gnu} utilities. The programming | |
167 | language features allow these utilitites to be combined. | |
168 | Files containing commands can be created, and become | |
ccc6cda3 | 169 | commands themselves. These new commands have the same status as |
bb70624e | 170 | system commands in directories such as @file{/bin}, allowing users |
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171 | or groups to establish custom environments to automate their common |
172 | tasks. | |
173 | ||
174 | Shells may be used interactively or non-interactively. In | |
175 | interactive mode, they accept input typed from the keyboard. | |
176 | When executing non-interactively, shells execute commands read | |
177 | from a file. | |
ccc6cda3 | 178 | |
bb70624e | 179 | A shell allows execution of @sc{gnu} commands, both synchronously and |
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180 | asynchronously. |
181 | The shell waits for synchronous commands to complete before accepting | |
182 | more input; asynchronous commands continue to execute in parallel | |
183 | with the shell while it reads and executes additional commands. | |
184 | The @dfn{redirection} constructs permit | |
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185 | fine-grained control of the input and output of those commands. |
186 | Moreover, the shell allows control over the contents of commands' | |
187 | environments. | |
bb70624e JA |
188 | |
189 | Shells also provide a small set of built-in | |
ccc6cda3 | 190 | commands (@dfn{builtins}) implementing functionality impossible |
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191 | or inconvenient to obtain via separate utilities. |
192 | For example, @code{cd}, @code{break}, @code{continue}, and | |
193 | @code{exec}) cannot be implemented outside of the shell because | |
194 | they directly manipulate the shell itself. | |
195 | The @code{history}, @code{getopts}, @code{kill}, or @code{pwd} | |
196 | builtins, among others, could be implemented in separate utilities, | |
197 | but they are more convenient to use as builtin commands. | |
198 | All of the shell builtins are described in | |
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199 | subsequent sections. |
200 | ||
201 | While executing commands is essential, most of the power (and | |
202 | complexity) of shells is due to their embedded programming | |
203 | languages. Like any high-level language, the shell provides | |
204 | variables, flow control constructs, quoting, and functions. | |
205 | ||
bb70624e | 206 | Shells offer features geared specifically for |
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207 | interactive use rather than to augment the programming language. |
208 | These interactive features include job control, command line | |
b80f6443 | 209 | editing, command history and aliases. Each of these features is |
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210 | described in this manual. |
211 | ||
212 | @node Definitions | |
213 | @chapter Definitions | |
214 | These definitions are used throughout the remainder of this manual. | |
215 | ||
216 | @table @code | |
217 | ||
218 | @item POSIX | |
219 | @cindex POSIX | |
220 | A family of open system standards based on Unix. Bash | |
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221 | is primarily concerned with the Shell and Utilities portion of the |
222 | @sc{posix} 1003.1 standard. | |
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223 | |
224 | @item blank | |
225 | A space or tab character. | |
226 | ||
227 | @item builtin | |
228 | @cindex builtin | |
229 | A command that is implemented internally by the shell itself, rather | |
230 | than by an executable program somewhere in the file system. | |
231 | ||
232 | @item control operator | |
233 | @cindex control operator | |
234 | A @code{word} that performs a control function. It is a @code{newline} | |
235 | or one of the following: | |
236 | @samp{||}, @samp{&&}, @samp{&}, @samp{;}, @samp{;;}, | |
237 | @samp{|}, @samp{(}, or @samp{)}. | |
238 | ||
239 | @item exit status | |
240 | @cindex exit status | |
f73dda09 JA |
241 | The value returned by a command to its caller. The value is restricted |
242 | to eight bits, so the maximum value is 255. | |
ccc6cda3 JA |
243 | |
244 | @item field | |
245 | @cindex field | |
246 | A unit of text that is the result of one of the shell expansions. After | |
247 | expansion, when executing a command, the resulting fields are used as | |
248 | the command name and arguments. | |
249 | ||
250 | @item filename | |
251 | @cindex filename | |
252 | A string of characters used to identify a file. | |
253 | ||
254 | @item job | |
255 | @cindex job | |
256 | A set of processes comprising a pipeline, and any processes descended | |
257 | from it, that are all in the same process group. | |
258 | ||
259 | @item job control | |
260 | @cindex job control | |
d166f048 JA |
261 | A mechanism by which users can selectively stop (suspend) and restart |
262 | (resume) execution of processes. | |
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263 | |
264 | @item metacharacter | |
265 | @cindex metacharacter | |
266 | A character that, when unquoted, separates words. A metacharacter is | |
267 | a @code{blank} or one of the following characters: | |
268 | @samp{|}, @samp{&}, @samp{;}, @samp{(}, @samp{)}, @samp{<}, or | |
269 | @samp{>}. | |
270 | ||
271 | @item name | |
272 | @cindex name | |
273 | @cindex identifier | |
274 | A @code{word} consisting solely of letters, numbers, and underscores, | |
275 | and beginning with a letter or underscore. @code{Name}s are used as | |
276 | shell variable and function names. | |
277 | Also referred to as an @code{identifier}. | |
278 | ||
279 | @item operator | |
280 | @cindex operator, shell | |
281 | A @code{control operator} or a @code{redirection operator}. | |
282 | @xref{Redirections}, for a list of redirection operators. | |
283 | ||
284 | @item process group | |
285 | @cindex process group | |
286 | A collection of related processes each having the same process | |
bb70624e | 287 | group @sc{id}. |
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288 | |
289 | @item process group ID | |
290 | @cindex process group ID | |
291 | A unique identifer that represents a @code{process group} | |
292 | during its lifetime. | |
293 | ||
294 | @item reserved word | |
295 | @cindex reserved word | |
296 | A @code{word} that has a special meaning to the shell. Most reserved | |
297 | words introduce shell flow control constructs, such as @code{for} and | |
298 | @code{while}. | |
299 | ||
300 | @item return status | |
301 | @cindex return status | |
302 | A synonym for @code{exit status}. | |
303 | ||
304 | @item signal | |
305 | @cindex signal | |
bb70624e | 306 | A mechanism by which a process may be notified by the kernel |
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307 | of an event occurring in the system. |
308 | ||
309 | @item special builtin | |
310 | @cindex special builtin | |
311 | A shell builtin command that has been classified as special by the | |
0628567a | 312 | @sc{posix} standard. |
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313 | |
314 | @item token | |
315 | @cindex token | |
316 | A sequence of characters considered a single unit by the shell. It is | |
317 | either a @code{word} or an @code{operator}. | |
318 | ||
319 | @item word | |
320 | @cindex word | |
321 | A @code{token} that is not an @code{operator}. | |
322 | @end table | |
323 | ||
324 | @node Basic Shell Features | |
325 | @chapter Basic Shell Features | |
326 | @cindex Bourne shell | |
327 | ||
328 | Bash is an acronym for @samp{Bourne-Again SHell}. | |
329 | The Bourne shell is | |
330 | the traditional Unix shell originally written by Stephen Bourne. | |
331 | All of the Bourne shell builtin commands are available in Bash, | |
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332 | The rules for evaluation and quoting are taken from the @sc{posix} |
333 | specification for the `standard' Unix shell. | |
ccc6cda3 | 334 | |
cce855bc | 335 | This chapter briefly summarizes the shell's `building blocks': |
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336 | commands, control structures, shell functions, shell @i{parameters}, |
337 | shell expansions, | |
338 | @i{redirections}, which are a way to direct input and output from | |
339 | and to named files, and how the shell executes commands. | |
340 | ||
341 | @menu | |
342 | * Shell Syntax:: What your input means to the shell. | |
cce855bc | 343 | * Shell Commands:: The types of commands you can use. |
ccc6cda3 | 344 | * Shell Functions:: Grouping commands by name. |
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345 | * Shell Parameters:: How the shell stores values. |
346 | * Shell Expansions:: How Bash expands parameters and the various | |
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347 | expansions available. |
348 | * Redirections:: A way to control where input and output go. | |
349 | * Executing Commands:: What happens when you run a command. | |
350 | * Shell Scripts:: Executing files of shell commands. | |
351 | @end menu | |
352 | ||
353 | @node Shell Syntax | |
354 | @section Shell Syntax | |
355 | @menu | |
356 | * Shell Operation:: The basic operation of the shell. | |
ccc6cda3 | 357 | * Quoting:: How to remove the special meaning from characters. |
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358 | * Comments:: How to specify comments. |
359 | @end menu | |
360 | ||
bb70624e JA |
361 | When the shell reads input, it proceeds through a |
362 | sequence of operations. If the input indicates the beginning of a | |
363 | comment, the shell ignores the comment symbol (@samp{#}), and the rest | |
364 | of that line. | |
365 | ||
366 | Otherwise, roughly speaking, the shell reads its input and | |
367 | divides the input into words and operators, employing the quoting rules | |
368 | to select which meanings to assign various words and characters. | |
369 | ||
370 | The shell then parses these tokens into commands and other constructs, | |
371 | removes the special meaning of certain words or characters, expands | |
372 | others, redirects input and output as needed, executes the specified | |
373 | command, waits for the command's exit status, and makes that exit status | |
374 | available for further inspection or processing. | |
375 | ||
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376 | @node Shell Operation |
377 | @subsection Shell Operation | |
378 | ||
379 | The following is a brief description of the shell's operation when it | |
380 | reads and executes a command. Basically, the shell does the | |
381 | following: | |
382 | ||
383 | @enumerate | |
384 | @item | |
385 | Reads its input from a file (@pxref{Shell Scripts}), from a string | |
28ef6c31 | 386 | supplied as an argument to the @option{-c} invocation option |
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387 | (@pxref{Invoking Bash}), or from the user's terminal. |
388 | ||
389 | @item | |
390 | Breaks the input into words and operators, obeying the quoting rules | |
cce855bc | 391 | described in @ref{Quoting}. These tokens are separated by |
ccc6cda3 JA |
392 | @code{metacharacters}. Alias expansion is performed by this step |
393 | (@pxref{Aliases}). | |
394 | ||
395 | @item | |
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396 | Parses the tokens into simple and compound commands |
397 | (@pxref{Shell Commands}). | |
ccc6cda3 JA |
398 | |
399 | @item | |
400 | Performs the various shell expansions (@pxref{Shell Expansions}), breaking | |
401 | the expanded tokens into lists of filenames (@pxref{Filename Expansion}) | |
402 | and commands and arguments. | |
403 | ||
404 | @item | |
405 | Performs any necessary redirections (@pxref{Redirections}) and removes | |
406 | the redirection operators and their operands from the argument list. | |
407 | ||
408 | @item | |
409 | Executes the command (@pxref{Executing Commands}). | |
410 | ||
411 | @item | |
412 | Optionally waits for the command to complete and collects its exit | |
cce855bc | 413 | status (@pxref{Exit Status}). |
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414 | |
415 | @end enumerate | |
416 | ||
417 | @node Quoting | |
418 | @subsection Quoting | |
419 | @cindex quoting | |
420 | @menu | |
421 | * Escape Character:: How to remove the special meaning from a single | |
422 | character. | |
423 | * Single Quotes:: How to inhibit all interpretation of a sequence | |
424 | of characters. | |
425 | * Double Quotes:: How to suppress most of the interpretation of a | |
426 | sequence of characters. | |
427 | * ANSI-C Quoting:: How to expand ANSI-C sequences in quoted strings. | |
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428 | * Locale Translation:: How to translate strings into different languages. |
429 | @end menu | |
430 | ||
431 | Quoting is used to remove the special meaning of certain | |
432 | characters or words to the shell. Quoting can be used to | |
433 | disable special treatment for special characters, to prevent | |
434 | reserved words from being recognized as such, and to prevent | |
435 | parameter expansion. | |
436 | ||
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437 | Each of the shell metacharacters (@pxref{Definitions}) |
438 | has special meaning to the shell and must be quoted if it is to | |
bb70624e | 439 | represent itself. |
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440 | When the command history expansion facilities are being used |
441 | (@pxref{History Interaction}), the | |
bb70624e | 442 | @var{history expansion} character, usually @samp{!}, must be quoted |
28ef6c31 | 443 | to prevent history expansion. @xref{Bash History Facilities}, for |
bb70624e | 444 | more details concerning history expansion. |
b80f6443 | 445 | |
bb70624e | 446 | There are three quoting mechanisms: the |
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447 | @var{escape character}, single quotes, and double quotes. |
448 | ||
449 | @node Escape Character | |
450 | @subsubsection Escape Character | |
451 | A non-quoted backslash @samp{\} is the Bash escape character. | |
452 | It preserves the literal value of the next character that follows, | |
453 | with the exception of @code{newline}. If a @code{\newline} pair | |
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454 | appears, and the backslash itself is not quoted, the @code{\newline} |
455 | is treated as a line continuation (that is, it is removed from | |
456 | the input stream and effectively ignored). | |
ccc6cda3 JA |
457 | |
458 | @node Single Quotes | |
459 | @subsubsection Single Quotes | |
460 | ||
bb70624e | 461 | Enclosing characters in single quotes (@samp{'}) preserves the literal value |
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462 | of each character within the quotes. A single quote may not occur |
463 | between single quotes, even when preceded by a backslash. | |
464 | ||
465 | @node Double Quotes | |
466 | @subsubsection Double Quotes | |
467 | ||
bb70624e | 468 | Enclosing characters in double quotes (@samp{"}) preserves the literal value |
ccc6cda3 | 469 | of all characters within the quotes, with the exception of |
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470 | @samp{$}, @samp{`}, @samp{\}, |
471 | and, when history expansion is enabled, @samp{!}. | |
ccc6cda3 | 472 | The characters @samp{$} and @samp{`} |
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473 | retain their special meaning within double quotes (@pxref{Shell Expansions}). |
474 | The backslash retains its special meaning only when followed by one of | |
475 | the following characters: | |
ccc6cda3 | 476 | @samp{$}, @samp{`}, @samp{"}, @samp{\}, or @code{newline}. |
cce855bc JA |
477 | Within double quotes, backslashes that are followed by one of these |
478 | characters are removed. Backslashes preceding characters without a | |
479 | special meaning are left unmodified. | |
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480 | A double quote may be quoted within double quotes by preceding it with |
481 | a backslash. | |
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482 | If enabled, history expansion will be performed unless an @samp{!} |
483 | appearing in double quotes is escaped using a backslash. | |
484 | The backslash preceding the @samp{!} is not removed. | |
ccc6cda3 JA |
485 | |
486 | The special parameters @samp{*} and @samp{@@} have special meaning | |
487 | when in double quotes (@pxref{Shell Parameter Expansion}). | |
488 | ||
489 | @node ANSI-C Quoting | |
490 | @subsubsection ANSI-C Quoting | |
491 | @cindex quoting, ANSI | |
492 | ||
493 | Words of the form @code{$'@var{string}'} are treated specially. The | |
494 | word expands to @var{string}, with backslash-escaped characters replaced | |
28ef6c31 | 495 | as specified by the ANSI C standard. Backslash escape sequences, if |
ccc6cda3 JA |
496 | present, are decoded as follows: |
497 | ||
498 | @table @code | |
499 | @item \a | |
500 | alert (bell) | |
501 | @item \b | |
502 | backspace | |
503 | @item \e | |
504 | an escape character (not ANSI C) | |
505 | @item \f | |
506 | form feed | |
507 | @item \n | |
508 | newline | |
509 | @item \r | |
510 | carriage return | |
511 | @item \t | |
512 | horizontal tab | |
513 | @item \v | |
514 | vertical tab | |
515 | @item \\ | |
516 | backslash | |
bb70624e JA |
517 | @item \' |
518 | single quote | |
ccc6cda3 | 519 | @item \@var{nnn} |
f73dda09 | 520 | the eight-bit character whose value is the octal value @var{nnn} |
cce855bc | 521 | (one to three digits) |
f73dda09 JA |
522 | @item \x@var{HH} |
523 | the eight-bit character whose value is the hexadecimal value @var{HH} | |
524 | (one or two hex digits) | |
7117c2d2 JA |
525 | @item \c@var{x} |
526 | a control-@var{x} character | |
ccc6cda3 JA |
527 | @end table |
528 | ||
529 | @noindent | |
bb70624e JA |
530 | The expanded result is single-quoted, as if the dollar sign had not |
531 | been present. | |
ccc6cda3 JA |
532 | |
533 | @node Locale Translation | |
534 | @subsubsection Locale-Specific Translation | |
535 | @cindex localization | |
f73dda09 JA |
536 | @cindex internationalization |
537 | @cindex native languages | |
538 | @cindex translation, native languages | |
ccc6cda3 JA |
539 | |
540 | A double-quoted string preceded by a dollar sign (@samp{$}) will cause | |
541 | the string to be translated according to the current locale. | |
542 | If the current locale is @code{C} or @code{POSIX}, the dollar sign | |
543 | is ignored. | |
544 | If the string is translated and replaced, the replacement is | |
545 | double-quoted. | |
546 | ||
f73dda09 JA |
547 | @vindex LC_MESSAGES |
548 | @vindex TEXTDOMAIN | |
549 | @vindex TEXTDOMAINDIR | |
28ef6c31 JA |
550 | Some systems use the message catalog selected by the @env{LC_MESSAGES} |
551 | shell variable. Others create the name of the message catalog from the | |
552 | value of the @env{TEXTDOMAIN} shell variable, possibly adding a | |
553 | suffix of @samp{.mo}. If you use the @env{TEXTDOMAIN} variable, you | |
554 | may need to set the @env{TEXTDOMAINDIR} variable to the location of | |
f73dda09 JA |
555 | the message catalog files. Still others use both variables in this |
556 | fashion: | |
557 | @env{TEXTDOMAINDIR}/@env{LC_MESSAGES}/LC_MESSAGES/@env{TEXTDOMAIN}.mo. | |
28ef6c31 | 558 | |
ccc6cda3 JA |
559 | @node Comments |
560 | @subsection Comments | |
561 | @cindex comments, shell | |
562 | ||
563 | In a non-interactive shell, or an interactive shell in which the | |
564 | @code{interactive_comments} option to the @code{shopt} | |
565 | builtin is enabled (@pxref{Bash Builtins}), | |
566 | a word beginning with @samp{#} | |
567 | causes that word and all remaining characters on that line to | |
568 | be ignored. An interactive shell without the @code{interactive_comments} | |
569 | option enabled does not allow comments. The @code{interactive_comments} | |
570 | option is on by default in interactive shells. | |
bb70624e | 571 | @xref{Interactive Shells}, for a description of what makes |
cce855bc JA |
572 | a shell interactive. |
573 | ||
574 | @node Shell Commands | |
575 | @section Shell Commands | |
576 | @cindex commands, shell | |
bb70624e JA |
577 | |
578 | A simple shell command such as @code{echo a b c} consists of the command | |
579 | itself followed by arguments, separated by spaces. | |
580 | ||
581 | More complex shell commands are composed of simple commands arranged together | |
582 | in a variety of ways: in a pipeline in which the output of one command | |
583 | becomes the input of a second, in a loop or conditional construct, or in | |
584 | some other grouping. | |
585 | ||
cce855bc JA |
586 | @menu |
587 | * Simple Commands:: The most common type of command. | |
588 | * Pipelines:: Connecting the input and output of several | |
589 | commands. | |
590 | * Lists:: How to execute commands sequentially. | |
b80f6443 | 591 | * Compound Commands:: Shell commands for control flow. |
cce855bc | 592 | @end menu |
ccc6cda3 JA |
593 | |
594 | @node Simple Commands | |
cce855bc | 595 | @subsection Simple Commands |
ccc6cda3 JA |
596 | @cindex commands, simple |
597 | ||
cce855bc | 598 | A simple command is the kind of command encountered most often. |
ccc6cda3 | 599 | It's just a sequence of words separated by @code{blank}s, terminated |
cce855bc | 600 | by one of the shell's control operators (@pxref{Definitions}). The |
bb70624e JA |
601 | first word generally specifies a command to be executed, with the |
602 | rest of the words being that command's arguments. | |
ccc6cda3 JA |
603 | |
604 | The return status (@pxref{Exit Status}) of a simple command is | |
605 | its exit status as provided | |
bb70624e JA |
606 | by the @sc{posix} 1003.1 @code{waitpid} function, or 128+@var{n} if |
607 | the command was terminated by signal @var{n}. | |
ccc6cda3 JA |
608 | |
609 | @node Pipelines | |
cce855bc | 610 | @subsection Pipelines |
ccc6cda3 JA |
611 | @cindex pipeline |
612 | @cindex commands, pipelines | |
613 | ||
614 | A @code{pipeline} is a sequence of simple commands separated by | |
615 | @samp{|}. | |
616 | ||
617 | @rwindex time | |
618 | @rwindex ! | |
619 | @cindex command timing | |
620 | The format for a pipeline is | |
621 | @example | |
622 | [@code{time} [@code{-p}]] [@code{!}] @var{command1} [@code{|} @var{command2} @dots{}] | |
623 | @end example | |
624 | ||
625 | @noindent | |
f73dda09 JA |
626 | The output of each command in the pipeline is connected via a pipe |
627 | to the input of the next command. | |
628 | That is, each command reads the previous command's output. | |
ccc6cda3 JA |
629 | |
630 | The reserved word @code{time} causes timing statistics | |
631 | to be printed for the pipeline once it finishes. | |
cce855bc JA |
632 | The statistics currently consist of elapsed (wall-clock) time and |
633 | user and system time consumed by the command's execution. | |
28ef6c31 | 634 | The @option{-p} option changes the output format to that specified |
bb70624e | 635 | by @sc{posix}. |
28ef6c31 | 636 | The @env{TIMEFORMAT} variable may be set to a format string that |
ccc6cda3 JA |
637 | specifies how the timing information should be displayed. |
638 | @xref{Bash Variables}, for a description of the available formats. | |
cce855bc JA |
639 | The use of @code{time} as a reserved word permits the timing of |
640 | shell builtins, shell functions, and pipelines. An external | |
641 | @code{time} command cannot time these easily. | |
642 | ||
643 | If the pipeline is not executed asynchronously (@pxref{Lists}), the | |
644 | shell waits for all commands in the pipeline to complete. | |
ccc6cda3 | 645 | |
cce855bc JA |
646 | Each command in a pipeline is executed in its own subshell |
647 | (@pxref{Command Execution Environment}). The exit | |
ccc6cda3 | 648 | status of a pipeline is the exit status of the last command in the |
b80f6443 JA |
649 | pipeline, unless the @code{pipefail} option is enabled |
650 | (@pxref{The Set Builtin}). | |
651 | If @code{pipefail} is enabled, the pipeline's return status is the | |
652 | value of the last (rightmost) command to exit with a non-zero status, | |
653 | or zero if all commands exit successfully. | |
654 | If the reserved word @samp{!} precedes the pipeline, the | |
655 | exit status is the logical negation of the exit status as described | |
656 | above. | |
657 | The shell waits for all commands in the pipeline to terminate before | |
658 | returning a value. | |
ccc6cda3 JA |
659 | |
660 | @node Lists | |
cce855bc | 661 | @subsection Lists of Commands |
ccc6cda3 JA |
662 | @cindex commands, lists |
663 | ||
664 | A @code{list} is a sequence of one or more pipelines separated by one | |
665 | of the operators @samp{;}, @samp{&}, @samp{&&}, or @samp{||}, | |
666 | and optionally terminated by one of @samp{;}, @samp{&}, or a | |
667 | @code{newline}. | |
668 | ||
669 | Of these list operators, @samp{&&} and @samp{||} | |
670 | have equal precedence, followed by @samp{;} and @samp{&}, | |
671 | which have equal precedence. | |
672 | ||
7117c2d2 JA |
673 | A sequence of one or more newlines may appear in a @code{list} |
674 | to delimit commands, equivalent to a semicolon. | |
675 | ||
ccc6cda3 | 676 | If a command is terminated by the control operator @samp{&}, |
cce855bc JA |
677 | the shell executes the command asynchronously in a subshell. |
678 | This is known as executing the command in the @var{background}. | |
679 | The shell does not wait for the command to finish, and the return | |
680 | status is 0 (true). | |
bb70624e JA |
681 | When job control is not active (@pxref{Job Control}), |
682 | the standard input for asynchronous commands, in the absence of any | |
cce855bc JA |
683 | explicit redirections, is redirected from @code{/dev/null}. |
684 | ||
685 | Commands separated by a @samp{;} are executed sequentially; the shell | |
686 | waits for each command to terminate in turn. The return status is the | |
ccc6cda3 JA |
687 | exit status of the last command executed. |
688 | ||
689 | The control operators @samp{&&} and @samp{||} | |
bb70624e JA |
690 | denote @sc{and} lists and @sc{or} lists, respectively. |
691 | An @sc{and} list has the form | |
ccc6cda3 | 692 | @example |
bb70624e | 693 | @var{command1} && @var{command2} |
ccc6cda3 JA |
694 | @end example |
695 | ||
696 | @noindent | |
bb70624e | 697 | @var{command2} is executed if, and only if, @var{command1} |
ccc6cda3 JA |
698 | returns an exit status of zero. |
699 | ||
bb70624e | 700 | An @sc{or} list has the form |
ccc6cda3 | 701 | @example |
bb70624e | 702 | @var{command1} || @var{command2} |
ccc6cda3 JA |
703 | @end example |
704 | ||
705 | @noindent | |
bb70624e | 706 | @var{command2} is executed if, and only if, @var{command1} |
ccc6cda3 JA |
707 | returns a non-zero exit status. |
708 | ||
709 | The return status of | |
bb70624e | 710 | @sc{and} and @sc{or} lists is the exit status of the last command |
ccc6cda3 JA |
711 | executed in the list. |
712 | ||
b80f6443 JA |
713 | @node Compound Commands |
714 | @subsection Compound Commands | |
715 | @cindex commands, compound | |
716 | ||
717 | @menu | |
718 | * Looping Constructs:: Shell commands for iterative action. | |
719 | * Conditional Constructs:: Shell commands for conditional execution. | |
720 | * Command Grouping:: Ways to group commands. | |
721 | @end menu | |
722 | ||
723 | Compound commands are the shell programming constructs. | |
724 | Each construct begins with a reserved word or control operator and is | |
725 | terminated by a corresponding reserved word or operator. | |
726 | Any redirections (@pxref{Redirections}) associated with a compound command | |
727 | apply to all commands within that compound command unless explicitly overridden. | |
728 | ||
729 | Bash provides looping constructs, conditional commands, and mechanisms | |
730 | to group commands and execute them as a unit. | |
731 | ||
ccc6cda3 | 732 | @node Looping Constructs |
b80f6443 | 733 | @subsubsection Looping Constructs |
ccc6cda3 JA |
734 | @cindex commands, looping |
735 | ||
ccc6cda3 JA |
736 | Bash supports the following looping constructs. |
737 | ||
bb70624e | 738 | Note that wherever a @samp{;} appears in the description of a |
cce855bc JA |
739 | command's syntax, it may be replaced with one or more newlines. |
740 | ||
ccc6cda3 JA |
741 | @table @code |
742 | @item until | |
743 | @rwindex until | |
744 | @rwindex do | |
745 | @rwindex done | |
746 | The syntax of the @code{until} command is: | |
747 | @example | |
748 | until @var{test-commands}; do @var{consequent-commands}; done | |
749 | @end example | |
cce855bc | 750 | Execute @var{consequent-commands} as long as |
ccc6cda3 | 751 | @var{test-commands} has an exit status which is not zero. |
cce855bc JA |
752 | The return status is the exit status of the last command executed |
753 | in @var{consequent-commands}, or zero if none was executed. | |
ccc6cda3 JA |
754 | |
755 | @item while | |
756 | @rwindex while | |
757 | The syntax of the @code{while} command is: | |
758 | @example | |
759 | while @var{test-commands}; do @var{consequent-commands}; done | |
760 | @end example | |
761 | ||
cce855bc | 762 | Execute @var{consequent-commands} as long as |
ccc6cda3 | 763 | @var{test-commands} has an exit status of zero. |
cce855bc JA |
764 | The return status is the exit status of the last command executed |
765 | in @var{consequent-commands}, or zero if none was executed. | |
ccc6cda3 JA |
766 | |
767 | @item for | |
768 | @rwindex for | |
769 | The syntax of the @code{for} command is: | |
770 | ||
771 | @example | |
772 | for @var{name} [in @var{words} @dots{}]; do @var{commands}; done | |
773 | @end example | |
cce855bc JA |
774 | Expand @var{words}, and execute @var{commands} once for each member |
775 | in the resultant list, with @var{name} bound to the current member. | |
bb70624e JA |
776 | If @samp{in @var{words}} is not present, the @code{for} command |
777 | executes the @var{commands} once for each positional parameter that is | |
778 | set, as if @samp{in "$@@"} had been specified | |
779 | (@pxref{Special Parameters}). | |
cce855bc JA |
780 | The return status is the exit status of the last command that executes. |
781 | If there are no items in the expansion of @var{words}, no commands are | |
782 | executed, and the return status is zero. | |
bb70624e JA |
783 | |
784 | An alternate form of the @code{for} command is also supported: | |
785 | ||
786 | @example | |
787 | for (( @var{expr1} ; @var{expr2} ; @var{expr3} )) ; do @var{commands} ; done | |
788 | @end example | |
789 | First, the arithmetic expression @var{expr1} is evaluated according | |
790 | to the rules described below (@pxref{Shell Arithmetic}). | |
791 | The arithmetic expression @var{expr2} is then evaluated repeatedly | |
792 | until it evaluates to zero. | |
793 | Each time @var{expr2} evaluates to a non-zero value, @var{commands} are | |
794 | executed and the arithmetic expression @var{expr3} is evaluated. | |
795 | If any expression is omitted, it behaves as if it evaluates to 1. | |
796 | The return value is the exit status of the last command in @var{list} | |
797 | that is executed, or false if any of the expressions is invalid. | |
798 | ||
ccc6cda3 JA |
799 | @end table |
800 | ||
801 | The @code{break} and @code{continue} builtins (@pxref{Bourne Shell Builtins}) | |
802 | may be used to control loop execution. | |
803 | ||
804 | @node Conditional Constructs | |
b80f6443 | 805 | @subsubsection Conditional Constructs |
ccc6cda3 JA |
806 | @cindex commands, conditional |
807 | ||
808 | @table @code | |
809 | @item if | |
810 | @rwindex if | |
811 | @rwindex then | |
812 | @rwindex else | |
813 | @rwindex elif | |
814 | @rwindex fi | |
815 | The syntax of the @code{if} command is: | |
816 | ||
817 | @example | |
818 | if @var{test-commands}; then | |
819 | @var{consequent-commands}; | |
820 | [elif @var{more-test-commands}; then | |
821 | @var{more-consequents};] | |
822 | [else @var{alternate-consequents};] | |
823 | fi | |
824 | @end example | |
825 | ||
cce855bc JA |
826 | The @var{test-commands} list is executed, and if its return status is zero, |
827 | the @var{consequent-commands} list is executed. | |
828 | If @var{test-commands} returns a non-zero status, each @code{elif} list | |
829 | is executed in turn, and if its exit status is zero, | |
ccc6cda3 JA |
830 | the corresponding @var{more-consequents} is executed and the |
831 | command completes. | |
832 | If @samp{else @var{alternate-consequents}} is present, and | |
833 | the final command in the final @code{if} or @code{elif} clause | |
cce855bc JA |
834 | has a non-zero exit status, then @var{alternate-consequents} is executed. |
835 | The return status is the exit status of the last command executed, or | |
836 | zero if no condition tested true. | |
ccc6cda3 JA |
837 | |
838 | @item case | |
839 | @rwindex case | |
840 | @rwindex in | |
841 | @rwindex esac | |
842 | The syntax of the @code{case} command is: | |
843 | ||
844 | @example | |
cce855bc | 845 | @code{case @var{word} in [ [(] @var{pattern} [| @var{pattern}]@dots{}) @var{command-list} ;;]@dots{} esac} |
ccc6cda3 JA |
846 | @end example |
847 | ||
cce855bc JA |
848 | @code{case} will selectively execute the @var{command-list} corresponding to |
849 | the first @var{pattern} that matches @var{word}. | |
95732b49 JA |
850 | If the shell option @code{nocasematch} |
851 | (see the description of @code{shopt} in @ref{Bash Builtins}) | |
852 | is enabled, the match is performed without regard to the case | |
853 | of alphabetic characters. | |
cce855bc JA |
854 | The @samp{|} is used to separate multiple patterns, and the @samp{)} |
855 | operator terminates a pattern list. | |
856 | A list of patterns and an associated command-list is known | |
857 | as a @var{clause}. Each clause must be terminated with @samp{;;}. | |
858 | The @var{word} undergoes tilde expansion, parameter expansion, command | |
859 | substitution, arithmetic expansion, and quote removal before matching is | |
860 | attempted. Each @var{pattern} undergoes tilde expansion, parameter | |
861 | expansion, command substitution, and arithmetic expansion. | |
862 | ||
863 | There may be an arbitrary number of @code{case} clauses, each terminated | |
864 | by a @samp{;;}. The first pattern that matches determines the | |
865 | command-list that is executed. | |
ccc6cda3 JA |
866 | |
867 | Here is an example using @code{case} in a script that could be used to | |
868 | describe one interesting feature of an animal: | |
869 | ||
870 | @example | |
871 | echo -n "Enter the name of an animal: " | |
872 | read ANIMAL | |
873 | echo -n "The $ANIMAL has " | |
874 | case $ANIMAL in | |
875 | horse | dog | cat) echo -n "four";; | |
876 | man | kangaroo ) echo -n "two";; | |
877 | *) echo -n "an unknown number of";; | |
878 | esac | |
879 | echo " legs." | |
880 | @end example | |
881 | ||
cce855bc JA |
882 | @noindent |
883 | The return status is zero if no @var{pattern} is matched. Otherwise, the | |
884 | return status is the exit status of the @var{command-list} executed. | |
885 | ||
886 | @item select | |
887 | @rwindex select | |
888 | ||
889 | The @code{select} construct allows the easy generation of menus. | |
890 | It has almost the same syntax as the @code{for} command: | |
891 | ||
892 | @example | |
893 | select @var{name} [in @var{words} @dots{}]; do @var{commands}; done | |
894 | @end example | |
895 | ||
896 | The list of words following @code{in} is expanded, generating a list | |
897 | of items. The set of expanded words is printed on the standard | |
898 | error output stream, each preceded by a number. If the | |
899 | @samp{in @var{words}} is omitted, the positional parameters are printed, | |
900 | as if @samp{in "$@@"} had been specifed. | |
28ef6c31 | 901 | The @env{PS3} prompt is then displayed and a line is read from the |
cce855bc JA |
902 | standard input. |
903 | If the line consists of a number corresponding to one of the displayed | |
904 | words, then the value of @var{name} is set to that word. | |
905 | If the line is empty, the words and prompt are displayed again. | |
906 | If @code{EOF} is read, the @code{select} command completes. | |
907 | Any other value read causes @var{name} to be set to null. | |
28ef6c31 | 908 | The line read is saved in the variable @env{REPLY}. |
cce855bc JA |
909 | |
910 | The @var{commands} are executed after each selection until a | |
f73dda09 | 911 | @code{break} command is executed, at which |
cce855bc JA |
912 | point the @code{select} command completes. |
913 | ||
914 | Here is an example that allows the user to pick a filename from the | |
915 | current directory, and displays the name and index of the file | |
916 | selected. | |
917 | ||
918 | @example | |
919 | select fname in *; | |
920 | do | |
921 | echo you picked $fname \($REPLY\) | |
922 | break; | |
923 | done | |
924 | @end example | |
925 | ||
ccc6cda3 JA |
926 | @item ((@dots{})) |
927 | @example | |
928 | (( @var{expression} )) | |
929 | @end example | |
930 | ||
cce855bc JA |
931 | The arithmetic @var{expression} is evaluated according to the rules |
932 | described below (@pxref{Shell Arithmetic}). | |
ccc6cda3 JA |
933 | If the value of the expression is non-zero, the return status is 0; |
934 | otherwise the return status is 1. This is exactly equivalent to | |
935 | @example | |
936 | let "@var{expression}" | |
937 | @end example | |
cce855bc JA |
938 | @noindent |
939 | @xref{Bash Builtins}, for a full description of the @code{let} builtin. | |
940 | ||
941 | @item [[@dots{}]] | |
942 | @rwindex [[ | |
943 | @rwindex ]] | |
944 | @example | |
945 | [[ @var{expression} ]] | |
946 | @end example | |
947 | ||
948 | Return a status of 0 or 1 depending on the evaluation of | |
949 | the conditional expression @var{expression}. | |
950 | Expressions are composed of the primaries described below in | |
951 | @ref{Bash Conditional Expressions}. | |
952 | Word splitting and filename expansion are not performed on the words | |
953 | between the @samp{[[} and @samp{]]}; tilde expansion, parameter and | |
954 | variable expansion, arithmetic expansion, command substitution, process | |
955 | substitution, and quote removal are performed. | |
b80f6443 JA |
956 | Conditional operators such as @samp{-f} must be unquoted to be recognized |
957 | as primaries. | |
cce855bc JA |
958 | |
959 | When the @samp{==} and @samp{!=} operators are used, the string to the | |
960 | right of the operator is considered a pattern and matched according | |
961 | to the rules described below in @ref{Pattern Matching}. | |
95732b49 JA |
962 | If the shell option @code{nocasematch} |
963 | (see the description of @code{shopt} in @ref{Bash Builtins}) | |
964 | is enabled, the match is performed without regard to the case | |
965 | of alphabetic characters. | |
0628567a JA |
966 | The return value is 0 if the string matches (@samp{==}) or does not |
967 | match (@samp{!=})the pattern, and 1 otherwise. | |
cce855bc JA |
968 | Any part of the pattern may be quoted to force it to be matched as a |
969 | string. | |
970 | ||
b80f6443 JA |
971 | An additional binary operator, @samp{=~}, is available, with the same |
972 | precedence as @samp{==} and @samp{!=}. | |
973 | When it is used, the string to the right of the operator is considered | |
974 | an extended regular expression and matched accordingly (as in @i{regex}3)). | |
975 | The return value is 0 if the string matches | |
976 | the pattern, and 1 otherwise. | |
977 | If the regular expression is syntactically incorrect, the conditional | |
978 | expression's return value is 2. | |
95732b49 | 979 | If the shell option @code{nocasematch} |
b80f6443 JA |
980 | (see the description of @code{shopt} in @ref{Bash Builtins}) |
981 | is enabled, the match is performed without regard to the case | |
982 | of alphabetic characters. | |
983 | Substrings matched by parenthesized subexpressions within the regular | |
984 | expression are saved in the array variable @code{BASH_REMATCH}. | |
985 | The element of @code{BASH_REMATCH} with index 0 is the portion of the string | |
986 | matching the entire regular expression. | |
987 | The element of @code{BASH_REMATCH} with index @var{n} is the portion of the | |
988 | string matching the @var{n}th parenthesized subexpression. | |
989 | ||
cce855bc JA |
990 | Expressions may be combined using the following operators, listed |
991 | in decreasing order of precedence: | |
992 | ||
993 | @table @code | |
994 | @item ( @var{expression} ) | |
995 | Returns the value of @var{expression}. | |
996 | This may be used to override the normal precedence of operators. | |
ccc6cda3 | 997 | |
cce855bc JA |
998 | @item ! @var{expression} |
999 | True if @var{expression} is false. | |
1000 | ||
1001 | @item @var{expression1} && @var{expression2} | |
1002 | True if both @var{expression1} and @var{expression2} are true. | |
1003 | ||
1004 | @item @var{expression1} || @var{expression2} | |
1005 | True if either @var{expression1} or @var{expression2} is true. | |
ccc6cda3 | 1006 | @end table |
cce855bc | 1007 | @noindent |
7117c2d2 | 1008 | The @code{&&} and @code{||} operators do not evaluate @var{expression2} if the |
cce855bc JA |
1009 | value of @var{expression1} is sufficient to determine the return |
1010 | value of the entire conditional expression. | |
ccc6cda3 | 1011 | |
cce855bc | 1012 | @end table |
ccc6cda3 JA |
1013 | |
1014 | @node Command Grouping | |
b80f6443 | 1015 | @subsubsection Grouping Commands |
ccc6cda3 JA |
1016 | @cindex commands, grouping |
1017 | ||
1018 | Bash provides two ways to group a list of commands to be executed | |
1019 | as a unit. When commands are grouped, redirections may be applied | |
1020 | to the entire command list. For example, the output of all the | |
1021 | commands in the list may be redirected to a single stream. | |
1022 | ||
1023 | @table @code | |
1024 | @item () | |
1025 | @example | |
1026 | ( @var{list} ) | |
1027 | @end example | |
1028 | ||
1029 | Placing a list of commands between parentheses causes a subshell | |
b80f6443 JA |
1030 | environment to be created (@pxref{Command Execution Environment}), and each |
1031 | of the commands in @var{list} to be executed in that subshell. Since the | |
1032 | @var{list} is executed in a subshell, variable assignments do not remain in | |
1033 | effect after the subshell completes. | |
ccc6cda3 JA |
1034 | |
1035 | @item @{@} | |
1036 | @rwindex @{ | |
1037 | @rwindex @} | |
1038 | @example | |
1039 | @{ @var{list}; @} | |
1040 | @end example | |
1041 | ||
1042 | Placing a list of commands between curly braces causes the list to | |
1043 | be executed in the current shell context. No subshell is created. | |
cce855bc | 1044 | The semicolon (or newline) following @var{list} is required. |
ccc6cda3 JA |
1045 | @end table |
1046 | ||
1047 | In addition to the creation of a subshell, there is a subtle difference | |
1048 | between these two constructs due to historical reasons. The braces | |
1049 | are @code{reserved words}, so they must be separated from the @var{list} | |
1050 | by @code{blank}s. The parentheses are @code{operators}, and are | |
1051 | recognized as separate tokens by the shell even if they are not separated | |
d166f048 | 1052 | from the @var{list} by whitespace. |
ccc6cda3 JA |
1053 | |
1054 | The exit status of both of these constructs is the exit status of | |
1055 | @var{list}. | |
1056 | ||
1057 | @node Shell Functions | |
1058 | @section Shell Functions | |
1059 | @cindex shell function | |
1060 | @cindex functions, shell | |
1061 | ||
1062 | Shell functions are a way to group commands for later execution | |
1063 | using a single name for the group. They are executed just like | |
bb70624e JA |
1064 | a "regular" command. |
1065 | When the name of a shell function is used as a simple command name, | |
1066 | the list of commands associated with that function name is executed. | |
1067 | Shell functions are executed in the current | |
ccc6cda3 JA |
1068 | shell context; no new process is created to interpret them. |
1069 | ||
1070 | Functions are declared using this syntax: | |
1071 | @rwindex function | |
1072 | @example | |
b80f6443 | 1073 | [ @code{function} ] @var{name} () @var{compound-command} [ @var{redirections} ] |
ccc6cda3 JA |
1074 | @end example |
1075 | ||
1076 | This defines a shell function named @var{name}. The reserved | |
cce855bc JA |
1077 | word @code{function} is optional. |
1078 | If the @code{function} reserved | |
1079 | word is supplied, the parentheses are optional. | |
b80f6443 JA |
1080 | The @var{body} of the function is the compound command |
1081 | @var{compound-command} (@pxref{Compound Commands}). | |
1082 | That command is usually a @var{list} enclosed between @{ and @}, but | |
1083 | may be any compound command listed above. | |
1084 | @var{compound-command} is executed whenever @var{name} is specified as the | |
1085 | name of a command. | |
1086 | Any redirections (@pxref{Redirections}) associated with the shell function | |
1087 | are performed when the function is executed. | |
1088 | ||
0628567a JA |
1089 | A function definition may be deleted using the @option{-f} option to the |
1090 | @code{unset} builtin (@pxref{Bourne Shell Builtins}). | |
1091 | ||
b80f6443 JA |
1092 | The exit status of a function definition is zero unless a syntax error |
1093 | occurs or a readonly function with the same name already exists. | |
1094 | When executed, the exit status of a function is the exit status of the | |
1095 | last command executed in the body. | |
1096 | ||
1097 | Note that for historical reasons, in the most common usage the curly braces | |
1098 | that surround the body of the function must be separated from the body by | |
bb70624e JA |
1099 | @code{blank}s or newlines. |
1100 | This is because the braces are reserved words and are only recognized | |
1101 | as such when they are separated by whitespace. | |
b80f6443 JA |
1102 | Also, when using the braces, the @var{list} must be terminated by a semicolon, |
1103 | a @samp{&}, or a newline. | |
bb70624e | 1104 | |
ccc6cda3 JA |
1105 | When a function is executed, the arguments to the |
1106 | function become the positional parameters | |
1107 | during its execution (@pxref{Positional Parameters}). | |
d166f048 JA |
1108 | The special parameter @samp{#} that expands to the number of |
1109 | positional parameters is updated to reflect the change. | |
b80f6443 JA |
1110 | Special parameter @code{0} is unchanged. |
1111 | The first element of the @env{FUNCNAME} variable is set to the | |
1112 | name of the function while the function is executing. | |
1113 | All other aspects of the shell execution | |
1114 | environment are identical between a function and its caller | |
95732b49 JA |
1115 | with the exception that the @env{DEBUG} and @env{RETURN} traps |
1116 | are not inherited unless the function has been given the | |
b80f6443 JA |
1117 | @code{trace} attribute using the @code{declare} builtin or |
1118 | the @code{-o functrace} option has been enabled with | |
1119 | the @code{set} builtin, | |
95732b49 | 1120 | (in which case all functions inherit the @env{DEBUG} and @env{RETURN} traps). |
b80f6443 JA |
1121 | @xref{Bourne Shell Builtins}, for the description of the |
1122 | @code{trap} builtin. | |
ccc6cda3 JA |
1123 | |
1124 | If the builtin command @code{return} | |
1125 | is executed in a function, the function completes and | |
1126 | execution resumes with the next command after the function | |
b80f6443 JA |
1127 | call. |
1128 | Any command associated with the @code{RETURN} trap is executed | |
1129 | before execution resumes. | |
1130 | When a function completes, the values of the | |
ccc6cda3 | 1131 | positional parameters and the special parameter @samp{#} |
cce855bc | 1132 | are restored to the values they had prior to the function's |
ccc6cda3 | 1133 | execution. If a numeric argument is given to @code{return}, |
f73dda09 | 1134 | that is the function's return status; otherwise the function's |
cce855bc JA |
1135 | return status is the exit status of the last command executed |
1136 | before the @code{return}. | |
ccc6cda3 JA |
1137 | |
1138 | Variables local to the function may be declared with the | |
1139 | @code{local} builtin. These variables are visible only to | |
1140 | the function and the commands it invokes. | |
1141 | ||
b80f6443 JA |
1142 | Function names and definitions may be listed with the |
1143 | @option{-f} option to the @code{declare} or @code{typeset} | |
1144 | builtin commands (@pxref{Bash Builtins}). | |
1145 | The @option{-F} option to @code{declare} or @code{typeset} | |
1146 | will list the function names only | |
1147 | (and optionally the source file and line number, if the @code{extdebug} | |
1148 | shell option is enabled). | |
1149 | Functions may be exported so that subshells | |
1150 | automatically have them defined with the | |
1151 | @option{-f} option to the @code{export} builtin | |
1152 | (@pxref{Bourne Shell Builtins}). | |
1153 | Note that shell functions and variables with the same name may result | |
1154 | in multiple identically-named entries in the environment passed to the | |
1155 | shell's children. | |
1156 | Care should be taken in cases where this may cause a problem. | |
1157 | ||
ccc6cda3 JA |
1158 | Functions may be recursive. No limit is placed on the number of |
1159 | recursive calls. | |
1160 | ||
1161 | @node Shell Parameters | |
1162 | @section Shell Parameters | |
1163 | @cindex parameters | |
1164 | @cindex variable, shell | |
1165 | @cindex shell variable | |
1166 | ||
1167 | @menu | |
1168 | * Positional Parameters:: The shell's command-line arguments. | |
b80f6443 | 1169 | * Special Parameters:: Parameters denoted by special characters. |
ccc6cda3 JA |
1170 | @end menu |
1171 | ||
1172 | A @var{parameter} is an entity that stores values. | |
1173 | It can be a @code{name}, a number, or one of the special characters | |
1174 | listed below. | |
b80f6443 | 1175 | A @var{variable} is a parameter denoted by a @code{name}. |
f73dda09 JA |
1176 | A variable has a @var{value} and zero or more @var{attributes}. |
1177 | Attributes are assigned using the @code{declare} builtin command | |
1178 | (see the description of the @code{declare} builtin in @ref{Bash Builtins}). | |
ccc6cda3 JA |
1179 | |
1180 | A parameter is set if it has been assigned a value. The null string is | |
1181 | a valid value. Once a variable is set, it may be unset only by using | |
1182 | the @code{unset} builtin command. | |
1183 | ||
1184 | A variable may be assigned to by a statement of the form | |
1185 | @example | |
1186 | @var{name}=[@var{value}] | |
1187 | @end example | |
1188 | @noindent | |
1189 | If @var{value} | |
1190 | is not given, the variable is assigned the null string. All | |
1191 | @var{value}s undergo tilde expansion, parameter and variable expansion, | |
1192 | command substitution, arithmetic expansion, and quote | |
cce855bc | 1193 | removal (detailed below). If the variable has its @code{integer} |
f73dda09 | 1194 | attribute set, then @var{value} |
b80f6443 | 1195 | is evaluated as an arithmetic expression even if the @code{$((@dots{}))} |
cce855bc | 1196 | expansion is not used (@pxref{Arithmetic Expansion}). |
ccc6cda3 JA |
1197 | Word splitting is not performed, with the exception |
1198 | of @code{"$@@"} as explained below. | |
1199 | Filename expansion is not performed. | |
f73dda09 | 1200 | Assignment statements may also appear as arguments to the |
b80f6443 | 1201 | @code{alias}, |
f73dda09 JA |
1202 | @code{declare}, @code{typeset}, @code{export}, @code{readonly}, |
1203 | and @code{local} builtin commands. | |
ccc6cda3 | 1204 | |
95732b49 JA |
1205 | In the context where an assignment statement is assigning a value |
1206 | to a shell variable or array index (@pxref{Arrays}), the @samp{+=} | |
1207 | operator can be used to | |
1208 | append to or add to the variable's previous value. | |
1209 | When @samp{+=} is applied to a variable for which the integer attribute | |
1210 | has been set, @var{value} is evaluated as an arithmetic expression and | |
1211 | added to the variable's current value, which is also evaluated. | |
1212 | When @samp{+=} is applied to an array variable using compound assignment | |
1213 | (@pxref{Arrays}), the | |
1214 | variable's value is not unset (as it is when using @samp{=}), and new | |
1215 | values are appended to the array beginning at one greater than the array's | |
1216 | maximum index. | |
1217 | When applied to a string-valued variable, @var{value} is expanded and | |
1218 | appended to the variable's value. | |
1219 | ||
ccc6cda3 JA |
1220 | @node Positional Parameters |
1221 | @subsection Positional Parameters | |
1222 | @cindex parameters, positional | |
1223 | ||
cce855bc | 1224 | A @var{positional parameter} is a parameter denoted by one or more |
ccc6cda3 JA |
1225 | digits, other than the single digit @code{0}. Positional parameters are |
1226 | assigned from the shell's arguments when it is invoked, | |
cce855bc | 1227 | and may be reassigned using the @code{set} builtin command. |
bb70624e JA |
1228 | Positional parameter @code{N} may be referenced as @code{$@{N@}}, or |
1229 | as @code{$N} when @code{N} consists of a single digit. | |
1230 | Positional parameters may not be assigned to with assignment statements. | |
1231 | The @code{set} and @code{shift} builtins are used to set and | |
1232 | unset them (@pxref{Shell Builtin Commands}). | |
1233 | The positional parameters are | |
ccc6cda3 JA |
1234 | temporarily replaced when a shell function is executed |
1235 | (@pxref{Shell Functions}). | |
1236 | ||
1237 | When a positional parameter consisting of more than a single | |
1238 | digit is expanded, it must be enclosed in braces. | |
1239 | ||
1240 | @node Special Parameters | |
1241 | @subsection Special Parameters | |
1242 | @cindex parameters, special | |
1243 | ||
1244 | The shell treats several parameters specially. These parameters may | |
1245 | only be referenced; assignment to them is not allowed. | |
1246 | ||
1247 | @vtable @code | |
1248 | ||
1249 | @item * | |
1250 | Expands to the positional parameters, starting from one. When the | |
1251 | expansion occurs within double quotes, it expands to a single word | |
1252 | with the value of each parameter separated by the first character | |
28ef6c31 | 1253 | of the @env{IFS} |
ccc6cda3 JA |
1254 | special variable. That is, @code{"$*"} is equivalent |
1255 | to @code{"$1@var{c}$2@var{c}@dots{}"}, where @var{c} | |
1256 | is the first character of the value of the @code{IFS} | |
d166f048 | 1257 | variable. |
28ef6c31 JA |
1258 | If @env{IFS} is unset, the parameters are separated by spaces. |
1259 | If @env{IFS} is null, the parameters are joined without intervening | |
d166f048 JA |
1260 | separators. |
1261 | ||
ccc6cda3 JA |
1262 | |
1263 | @item @@ | |
1264 | Expands to the positional parameters, starting from one. When the | |
cce855bc | 1265 | expansion occurs within double quotes, each parameter expands to a |
ccc6cda3 JA |
1266 | separate word. That is, @code{"$@@"} is equivalent to |
1267 | @code{"$1" "$2" @dots{}}. | |
95732b49 JA |
1268 | If the double-quoted expansion occurs within a word, the expansion of |
1269 | the first parameter is joined with the beginning part of the original | |
1270 | word, and the expansion of the last parameter is joined with the last | |
1271 | part of the original word. | |
ccc6cda3 JA |
1272 | When there are no positional parameters, @code{"$@@"} and |
1273 | @code{$@@} | |
1274 | expand to nothing (i.e., they are removed). | |
1275 | ||
1276 | @item # | |
1277 | Expands to the number of positional parameters in decimal. | |
1278 | ||
1279 | @item ? | |
1280 | Expands to the exit status of the most recently executed foreground | |
1281 | pipeline. | |
1282 | ||
1283 | @item - | |
bb70624e JA |
1284 | (A hyphen.) Expands to the current option flags as specified upon |
1285 | invocation, by the @code{set} | |
ccc6cda3 | 1286 | builtin command, or those set by the shell itself |
28ef6c31 | 1287 | (such as the @option{-i} option). |
ccc6cda3 JA |
1288 | |
1289 | @item $ | |
bb70624e JA |
1290 | Expands to the process @sc{id} of the shell. In a @code{()} subshell, it |
1291 | expands to the process @sc{id} of the invoking shell, not the subshell. | |
ccc6cda3 JA |
1292 | |
1293 | @item ! | |
bb70624e | 1294 | Expands to the process @sc{id} of the most recently executed background |
ccc6cda3 JA |
1295 | (asynchronous) command. |
1296 | ||
1297 | @item 0 | |
1298 | Expands to the name of the shell or shell script. This is set at | |
cce855bc JA |
1299 | shell initialization. If Bash is invoked with a file of commands |
1300 | (@pxref{Shell Scripts}), @code{$0} is set to the name of that file. | |
28ef6c31 | 1301 | If Bash is started with the @option{-c} option (@pxref{Invoking Bash}), |
cce855bc | 1302 | then @code{$0} is set to the first argument after the string to be |
ccc6cda3 JA |
1303 | executed, if one is present. Otherwise, it is set |
1304 | to the filename used to invoke Bash, as given by argument zero. | |
1305 | ||
1306 | @item _ | |
bb70624e | 1307 | (An underscore.) |
95732b49 JA |
1308 | At shell startup, set to the absolute pathname used to invoke the |
1309 | shell or shell script being executed as passed in the environment | |
1310 | or argument list. | |
ccc6cda3 JA |
1311 | Subsequently, expands to the last argument to the previous command, |
1312 | after expansion. | |
95732b49 JA |
1313 | Also set to the full pathname used to invoke each command executed |
1314 | and placed in the environment exported to that command. | |
ccc6cda3 JA |
1315 | When checking mail, this parameter holds the name of the mail file. |
1316 | @end vtable | |
1317 | ||
1318 | @node Shell Expansions | |
1319 | @section Shell Expansions | |
1320 | @cindex expansion | |
1321 | ||
1322 | Expansion is performed on the command line after it has been split into | |
1323 | @code{token}s. There are seven kinds of expansion performed: | |
1324 | @itemize @bullet | |
1325 | @item brace expansion | |
1326 | @item tilde expansion | |
1327 | @item parameter and variable expansion | |
1328 | @item command substitution | |
1329 | @item arithmetic expansion | |
1330 | @item word splitting | |
1331 | @item filename expansion | |
1332 | @end itemize | |
1333 | ||
1334 | @menu | |
cce855bc JA |
1335 | * Brace Expansion:: Expansion of expressions within braces. |
1336 | * Tilde Expansion:: Expansion of the ~ character. | |
ccc6cda3 JA |
1337 | * Shell Parameter Expansion:: How Bash expands variables to their values. |
1338 | * Command Substitution:: Using the output of a command as an argument. | |
cce855bc | 1339 | * Arithmetic Expansion:: How to use arithmetic in shell expansions. |
ccc6cda3 JA |
1340 | * Process Substitution:: A way to write and read to and from a |
1341 | command. | |
1342 | * Word Splitting:: How the results of expansion are split into separate | |
1343 | arguments. | |
1344 | * Filename Expansion:: A shorthand for specifying filenames matching patterns. | |
1345 | * Quote Removal:: How and when quote characters are removed from | |
1346 | words. | |
1347 | @end menu | |
1348 | ||
ccc6cda3 JA |
1349 | The order of expansions is: brace expansion, tilde expansion, |
1350 | parameter, variable, and arithmetic expansion and | |
1351 | command substitution | |
1352 | (done in a left-to-right fashion), word splitting, and filename | |
1353 | expansion. | |
1354 | ||
1355 | On systems that can support it, there is an additional expansion | |
1356 | available: @var{process substitution}. This is performed at the | |
cce855bc | 1357 | same time as parameter, variable, and arithmetic expansion and |
ccc6cda3 JA |
1358 | command substitution. |
1359 | ||
1360 | Only brace expansion, word splitting, and filename expansion | |
1361 | can change the number of words of the expansion; other expansions | |
1362 | expand a single word to a single word. | |
1363 | The only exceptions to this are the expansions of | |
d166f048 | 1364 | @code{"$@@"} (@pxref{Special Parameters}) and @code{"$@{@var{name}[@@]@}"} |
ccc6cda3 JA |
1365 | (@pxref{Arrays}). |
1366 | ||
1367 | After all expansions, @code{quote removal} (@pxref{Quote Removal}) | |
1368 | is performed. | |
1369 | ||
cce855bc JA |
1370 | @node Brace Expansion |
1371 | @subsection Brace Expansion | |
1372 | @cindex brace expansion | |
1373 | @cindex expansion, brace | |
1374 | ||
bb70624e JA |
1375 | Brace expansion is a mechanism by which arbitrary strings may be generated. |
1376 | This mechanism is similar to | |
cce855bc | 1377 | @var{filename expansion} (@pxref{Filename Expansion}), |
bb70624e JA |
1378 | but the file names generated need not exist. |
1379 | Patterns to be brace expanded take the form of an optional @var{preamble}, | |
b80f6443 JA |
1380 | followed by either a series of comma-separated strings or a sequnce expression |
1381 | between a pair of braces, | |
bb70624e JA |
1382 | followed by an optional @var{postscript}. |
1383 | The preamble is prefixed to each string contained within the braces, and | |
1384 | the postscript is then appended to each resulting string, expanding left | |
1385 | to right. | |
1386 | ||
1387 | Brace expansions may be nested. | |
1388 | The results of each expanded string are not sorted; left to right order | |
1389 | is preserved. | |
cce855bc JA |
1390 | For example, |
1391 | @example | |
1392 | bash$ echo a@{d,c,b@}e | |
1393 | ade ace abe | |
1394 | @end example | |
1395 | ||
b80f6443 JA |
1396 | A sequence expression takes the form @code{@{@var{x}..@var{y}@}}, |
1397 | where @var{x} and @var{y} are either integers or single characters. | |
1398 | When integers are supplied, the expression expands to each number between | |
1399 | @var{x} and @var{y}, inclusive. | |
1400 | When characters are supplied, the expression expands to each character | |
1401 | lexicographically between @var{x} and @var{y}, inclusive. Note that | |
1402 | both @var{x} and @var{y} must be of the same type. | |
1403 | ||
cce855bc JA |
1404 | Brace expansion is performed before any other expansions, |
1405 | and any characters special to other expansions are preserved | |
1406 | in the result. It is strictly textual. Bash | |
1407 | does not apply any syntactic interpretation to the context of the | |
1408 | expansion or the text between the braces. | |
bb70624e JA |
1409 | To avoid conflicts with parameter expansion, the string @samp{$@{} |
1410 | is not considered eligible for brace expansion. | |
cce855bc JA |
1411 | |
1412 | A correctly-formed brace expansion must contain unquoted opening | |
b80f6443 JA |
1413 | and closing braces, and at least one unquoted comma or a valid |
1414 | sequence expression. | |
cce855bc JA |
1415 | Any incorrectly formed brace expansion is left unchanged. |
1416 | ||
b80f6443 JA |
1417 | A @{ or @samp{,} may be quoted with a backslash to prevent its |
1418 | being considered part of a brace expression. | |
1419 | To avoid conflicts with parameter expansion, the string @samp{$@{} | |
1420 | is not considered eligible for brace expansion. | |
1421 | ||
cce855bc JA |
1422 | This construct is typically used as shorthand when the common |
1423 | prefix of the strings to be generated is longer than in the | |
1424 | above example: | |
1425 | @example | |
1426 | mkdir /usr/local/src/bash/@{old,new,dist,bugs@} | |
1427 | @end example | |
1428 | or | |
1429 | @example | |
1430 | chown root /usr/@{ucb/@{ex,edit@},lib/@{ex?.?*,how_ex@}@} | |
1431 | @end example | |
1432 | ||
1433 | @node Tilde Expansion | |
1434 | @subsection Tilde Expansion | |
1435 | @cindex tilde expansion | |
1436 | @cindex expansion, tilde | |
1437 | ||
1438 | If a word begins with an unquoted tilde character (@samp{~}), all of the | |
1439 | characters up to the first unquoted slash (or all characters, | |
1440 | if there is no unquoted slash) are considered a @var{tilde-prefix}. | |
1441 | If none of the characters in the tilde-prefix are quoted, the | |
1442 | characters in the tilde-prefix following the tilde are treated as a | |
1443 | possible @var{login name}. | |
1444 | If this login name is the null string, the tilde is replaced with the | |
28ef6c31 JA |
1445 | value of the @env{HOME} shell variable. |
1446 | If @env{HOME} is unset, the home directory of the user executing the | |
cce855bc JA |
1447 | shell is substituted instead. |
1448 | Otherwise, the tilde-prefix is replaced with the home directory | |
1449 | associated with the specified login name. | |
1450 | ||
1451 | If the tilde-prefix is @samp{~+}, the value of | |
28ef6c31 | 1452 | the shell variable @env{PWD} replaces the tilde-prefix. |
cce855bc | 1453 | If the tilde-prefix is @samp{~-}, the value of the shell variable |
28ef6c31 | 1454 | @env{OLDPWD}, if it is set, is substituted. |
cce855bc JA |
1455 | |
1456 | If the characters following the tilde in the tilde-prefix consist of a | |
1457 | number @var{N}, optionally prefixed by a @samp{+} or a @samp{-}, | |
1458 | the tilde-prefix is replaced with the | |
1459 | corresponding element from the directory stack, as it would be displayed | |
1460 | by the @code{dirs} builtin invoked with the characters following tilde | |
1461 | in the tilde-prefix as an argument (@pxref{The Directory Stack}). | |
1462 | If the tilde-prefix, sans the tilde, consists of a number without a | |
1463 | leading @samp{+} or @samp{-}, @samp{+} is assumed. | |
1464 | ||
1465 | If the login name is invalid, or the tilde expansion fails, the word is | |
1466 | left unchanged. | |
1467 | ||
1468 | Each variable assignment is checked for unquoted tilde-prefixes immediately | |
95732b49 | 1469 | following a @samp{:} or the first @samp{=}. |
cce855bc JA |
1470 | In these cases, tilde expansion is also performed. |
1471 | Consequently, one may use file names with tildes in assignments to | |
28ef6c31 | 1472 | @env{PATH}, @env{MAILPATH}, and @env{CDPATH}, |
cce855bc JA |
1473 | and the shell assigns the expanded value. |
1474 | ||
1475 | The following table shows how Bash treats unquoted tilde-prefixes: | |
1476 | ||
1477 | @table @code | |
1478 | @item ~ | |
1479 | The value of @code{$HOME} | |
1480 | @item ~/foo | |
1481 | @file{$HOME/foo} | |
1482 | ||
1483 | @item ~fred/foo | |
1484 | The subdirectory @code{foo} of the home directory of the user | |
1485 | @code{fred} | |
1486 | ||
1487 | @item ~+/foo | |
1488 | @file{$PWD/foo} | |
1489 | ||
1490 | @item ~-/foo | |
1491 | @file{$@{OLDPWD-'~-'@}/foo} | |
1492 | ||
1493 | @item ~@var{N} | |
1494 | The string that would be displayed by @samp{dirs +@var{N}} | |
1495 | ||
1496 | @item ~+@var{N} | |
1497 | The string that would be displayed by @samp{dirs +@var{N}} | |
1498 | ||
1499 | @item ~-@var{N} | |
1500 | The string that would be displayed by @samp{dirs -@var{N}} | |
1501 | ||
1502 | @end table | |
1503 | ||
ccc6cda3 JA |
1504 | @node Shell Parameter Expansion |
1505 | @subsection Shell Parameter Expansion | |
1506 | @cindex parameter expansion | |
1507 | @cindex expansion, parameter | |
1508 | ||
1509 | The @samp{$} character introduces parameter expansion, | |
1510 | command substitution, or arithmetic expansion. The parameter name | |
1511 | or symbol to be expanded may be enclosed in braces, which | |
1512 | are optional but serve to protect the variable to be expanded from | |
1513 | characters immediately following it which could be | |
1514 | interpreted as part of the name. | |
1515 | ||
cce855bc JA |
1516 | When braces are used, the matching ending brace is the first @samp{@}} |
1517 | not escaped by a backslash or within a quoted string, and not within an | |
1518 | embedded arithmetic expansion, command substitution, or parameter | |
1519 | expansion. | |
1520 | ||
ccc6cda3 JA |
1521 | The basic form of parameter expansion is $@{@var{parameter}@}. |
1522 | The value of @var{parameter} is substituted. The braces are required | |
1523 | when @var{parameter} | |
1524 | is a positional parameter with more than one digit, | |
1525 | or when @var{parameter} | |
1526 | is followed by a character that is not to be | |
1527 | interpreted as part of its name. | |
1528 | ||
1529 | If the first character of @var{parameter} is an exclamation point, | |
1530 | a level of variable indirection is introduced. | |
1531 | Bash uses the value of the variable formed from the rest of | |
1532 | @var{parameter} as the name of the variable; this variable is then | |
d166f048 | 1533 | expanded and that value is used in the rest of the substitution, rather |
ccc6cda3 JA |
1534 | than the value of @var{parameter} itself. |
1535 | This is known as @code{indirect expansion}. | |
b80f6443 JA |
1536 | The exceptions to this are the expansions of $@{!@var{prefix*}@} |
1537 | and $@{!@var{name}[@@]@} | |
bb70624e | 1538 | described below. |
b80f6443 JA |
1539 | The exclamation point must immediately follow the left brace in order to |
1540 | introduce indirection. | |
ccc6cda3 JA |
1541 | |
1542 | In each of the cases below, @var{word} is subject to tilde expansion, | |
1543 | parameter expansion, command substitution, and arithmetic expansion. | |
bb70624e | 1544 | |
ccc6cda3 JA |
1545 | When not performing substring expansion, Bash tests for a parameter |
1546 | that is unset or null; omitting the colon results in a test only for a | |
bb70624e JA |
1547 | parameter that is unset. Put another way, if the colon is included, |
1548 | the operator tests for both existence and that the value is not null; | |
1549 | if the colon is omitted, the operator tests only for existence. | |
ccc6cda3 JA |
1550 | |
1551 | @table @code | |
1552 | ||
1553 | @item $@{@var{parameter}:@minus{}@var{word}@} | |
1554 | If @var{parameter} is unset or null, the expansion of | |
1555 | @var{word} is substituted. Otherwise, the value of | |
1556 | @var{parameter} is substituted. | |
1557 | ||
1558 | @item $@{@var{parameter}:=@var{word}@} | |
1559 | If @var{parameter} | |
1560 | is unset or null, the expansion of @var{word} | |
1561 | is assigned to @var{parameter}. | |
b80f6443 JA |
1562 | The value of @var{parameter} is then substituted. |
1563 | Positional parameters and special parameters may not be assigned to | |
1564 | in this way. | |
ccc6cda3 JA |
1565 | |
1566 | @item $@{@var{parameter}:?@var{word}@} | |
1567 | If @var{parameter} | |
1568 | is null or unset, the expansion of @var{word} (or a message | |
1569 | to that effect if @var{word} | |
1570 | is not present) is written to the standard error and the shell, if it | |
1571 | is not interactive, exits. Otherwise, the value of @var{parameter} is | |
1572 | substituted. | |
1573 | ||
1574 | @item $@{@var{parameter}:+@var{word}@} | |
1575 | If @var{parameter} | |
1576 | is null or unset, nothing is substituted, otherwise the expansion of | |
1577 | @var{word} is substituted. | |
1578 | ||
1579 | @item $@{@var{parameter}:@var{offset}@} | |
1580 | @itemx $@{@var{parameter}:@var{offset}:@var{length}@} | |
bb70624e | 1581 | Expands to up to @var{length} characters of @var{parameter} |
cce855bc | 1582 | starting at the character specified by @var{offset}. |
ccc6cda3 | 1583 | If @var{length} is omitted, expands to the substring of |
bb70624e | 1584 | @var{parameter} starting at the character specified by @var{offset}. |
ccc6cda3 | 1585 | @var{length} and @var{offset} are arithmetic expressions |
cce855bc | 1586 | (@pxref{Shell Arithmetic}). |
ccc6cda3 JA |
1587 | This is referred to as Substring Expansion. |
1588 | ||
1589 | @var{length} must evaluate to a number greater than or equal to zero. | |
1590 | If @var{offset} evaluates to a number less than zero, the value | |
1591 | is used as an offset from the end of the value of @var{parameter}. | |
1592 | If @var{parameter} is @samp{@@}, the result is @var{length} positional | |
1593 | parameters beginning at @var{offset}. | |
1594 | If @var{parameter} is an array name indexed by @samp{@@} or @samp{*}, | |
1595 | the result is the @var{length} | |
cce855bc | 1596 | members of the array beginning with @code{$@{@var{parameter}[@var{offset}]@}}. |
95732b49 JA |
1597 | A negative @var{offset} is taken relative to one greater than the maximum |
1598 | index of the specified array. | |
1599 | Note that a negative offset must be separated from the colon by at least | |
1600 | one space to avoid being confused with the @samp{:-} expansion. | |
cce855bc JA |
1601 | Substring indexing is zero-based unless the positional parameters |
1602 | are used, in which case the indexing starts at 1. | |
ccc6cda3 | 1603 | |
bb70624e | 1604 | @item $@{!@var{prefix}*@} |
b80f6443 | 1605 | @itemx $@{!@var{prefix}@@@} |
bb70624e | 1606 | Expands to the names of variables whose names begin with @var{prefix}, |
28ef6c31 | 1607 | separated by the first character of the @env{IFS} special variable. |
bb70624e | 1608 | |
b80f6443 JA |
1609 | @item $@{!@var{name}[@@]@} |
1610 | @itemx $@{!@var{name}[*]@} | |
1611 | If @var{name} is an array variable, expands to the list of array indices | |
1612 | (keys) assigned in @var{name}. | |
1613 | If @var{name} is not an array, expands to 0 if @var{name} is set and null | |
1614 | otherwise. | |
1615 | When @samp{@@} is used and the expansion appears within double quotes, each | |
1616 | key expands to a separate word. | |
1617 | ||
ccc6cda3 | 1618 | @item $@{#@var{parameter}@} |
cce855bc JA |
1619 | The length in characters of the expanded value of @var{parameter} is |
1620 | substituted. | |
1621 | If @var{parameter} is @samp{*} or @samp{@@}, the value substituted | |
1622 | is the number of positional parameters. | |
1623 | If @var{parameter} is an array name subscripted by @samp{*} or @samp{@@}, | |
1624 | the value substituted is the number of elements in the array. | |
ccc6cda3 JA |
1625 | |
1626 | @item $@{@var{parameter}#@var{word}@} | |
1627 | @itemx $@{@var{parameter}##@var{word}@} | |
1628 | The @var{word} | |
1629 | is expanded to produce a pattern just as in filename | |
1630 | expansion (@pxref{Filename Expansion}). If the pattern matches | |
cce855bc JA |
1631 | the beginning of the expanded value of @var{parameter}, |
1632 | then the result of the expansion is the expanded value of @var{parameter} | |
ccc6cda3 JA |
1633 | with the shortest matching pattern (the @samp{#} case) or the |
1634 | longest matching pattern (the @samp{##} case) deleted. | |
1635 | If @var{parameter} is @samp{@@} or @samp{*}, | |
1636 | the pattern removal operation is applied to each positional | |
1637 | parameter in turn, and the expansion is the resultant list. | |
1638 | If @var{parameter} is an array variable subscripted with | |
1639 | @samp{@@} or @samp{*}, | |
1640 | the pattern removal operation is applied to each member of the | |
1641 | array in turn, and the expansion is the resultant list. | |
1642 | ||
1643 | @item $@{@var{parameter}%@var{word}@} | |
1644 | @itemx $@{@var{parameter}%%@var{word}@} | |
1645 | The @var{word} is expanded to produce a pattern just as in | |
1646 | filename expansion. | |
cce855bc JA |
1647 | If the pattern matches a trailing portion of the expanded value of |
1648 | @var{parameter}, then the result of the expansion is the value of | |
1649 | @var{parameter} with the shortest matching pattern (the @samp{%} case) | |
1650 | or the longest matching pattern (the @samp{%%} case) deleted. | |
ccc6cda3 JA |
1651 | If @var{parameter} is @samp{@@} or @samp{*}, |
1652 | the pattern removal operation is applied to each positional | |
1653 | parameter in turn, and the expansion is the resultant list. | |
1654 | If @var{parameter} | |
1655 | is an array variable subscripted with @samp{@@} or @samp{*}, | |
1656 | the pattern removal operation is applied to each member of the | |
1657 | array in turn, and the expansion is the resultant list. | |
1658 | ||
1659 | @item $@{@var{parameter}/@var{pattern}/@var{string}@} | |
ccc6cda3 JA |
1660 | |
1661 | The @var{pattern} is expanded to produce a pattern just as in | |
1662 | filename expansion. | |
1663 | @var{Parameter} is expanded and the longest match of @var{pattern} | |
1664 | against its value is replaced with @var{string}. | |
0628567a JA |
1665 | If @var{pattern} begins with @samp{/}, all matches of @var{pattern} are |
1666 | replaced with @var{string}. Normally only the first match is replaced. | |
ccc6cda3 | 1667 | If @var{pattern} begins with @samp{#}, it must match at the beginning |
b72432fd | 1668 | of the expanded value of @var{parameter}. |
ccc6cda3 | 1669 | If @var{pattern} begins with @samp{%}, it must match at the end |
b72432fd | 1670 | of the expanded value of @var{parameter}. |
ccc6cda3 JA |
1671 | If @var{string} is null, matches of @var{pattern} are deleted |
1672 | and the @code{/} following @var{pattern} may be omitted. | |
1673 | If @var{parameter} is @samp{@@} or @samp{*}, | |
1674 | the substitution operation is applied to each positional | |
1675 | parameter in turn, and the expansion is the resultant list. | |
1676 | If @var{parameter} | |
1677 | is an array variable subscripted with @samp{@@} or @samp{*}, | |
1678 | the substitution operation is applied to each member of the | |
1679 | array in turn, and the expansion is the resultant list. | |
1680 | ||
1681 | @end table | |
1682 | ||
1683 | @node Command Substitution | |
1684 | @subsection Command Substitution | |
1685 | @cindex command substitution | |
1686 | ||
1687 | Command substitution allows the output of a command to replace | |
bb70624e JA |
1688 | the command itself. |
1689 | Command substitution occurs when a command is enclosed as follows: | |
ccc6cda3 JA |
1690 | @example |
1691 | $(@var{command}) | |
1692 | @end example | |
1693 | @noindent | |
1694 | or | |
1695 | @example | |
1696 | `@var{command}` | |
1697 | @end example | |
1698 | ||
1699 | @noindent | |
1700 | Bash performs the expansion by executing @var{command} and | |
1701 | replacing the command substitution with the standard output of the | |
1702 | command, with any trailing newlines deleted. | |
cce855bc JA |
1703 | Embedded newlines are not deleted, but they may be removed during |
1704 | word splitting. | |
1705 | The command substitution @code{$(cat @var{file})} can be | |
1706 | replaced by the equivalent but faster @code{$(< @var{file})}. | |
ccc6cda3 JA |
1707 | |
1708 | When the old-style backquote form of substitution is used, | |
1709 | backslash retains its literal meaning except when followed by | |
cce855bc JA |
1710 | @samp{$}, @samp{`}, or @samp{\}. |
1711 | The first backquote not preceded by a backslash terminates the | |
1712 | command substitution. | |
ccc6cda3 JA |
1713 | When using the @code{$(@var{command})} form, all characters between |
1714 | the parentheses make up the command; none are treated specially. | |
1715 | ||
cce855bc JA |
1716 | Command substitutions may be nested. To nest when using the backquoted |
1717 | form, escape the inner backquotes with backslashes. | |
ccc6cda3 JA |
1718 | |
1719 | If the substitution appears within double quotes, word splitting and | |
1720 | filename expansion are not performed on the results. | |
1721 | ||
cce855bc JA |
1722 | @node Arithmetic Expansion |
1723 | @subsection Arithmetic Expansion | |
1724 | @cindex expansion, arithmetic | |
1725 | @cindex arithmetic expansion | |
1726 | ||
1727 | Arithmetic expansion allows the evaluation of an arithmetic expression | |
1728 | and the substitution of the result. The format for arithmetic expansion is: | |
1729 | ||
1730 | @example | |
1731 | $(( @var{expression} )) | |
1732 | @end example | |
1733 | ||
1734 | The expression is treated as if it were within double quotes, but | |
1735 | a double quote inside the parentheses is not treated specially. | |
1736 | All tokens in the expression undergo parameter expansion, command | |
1737 | substitution, and quote removal. | |
b80f6443 | 1738 | Arithmetic expansions may be nested. |
cce855bc JA |
1739 | |
1740 | The evaluation is performed according to the rules listed below | |
1741 | (@pxref{Shell Arithmetic}). | |
1742 | If the expression is invalid, Bash prints a message indicating | |
1743 | failure to the standard error and no substitution occurs. | |
1744 | ||
ccc6cda3 JA |
1745 | @node Process Substitution |
1746 | @subsection Process Substitution | |
1747 | @cindex process substitution | |
1748 | ||
1749 | Process substitution is supported on systems that support named | |
bb70624e | 1750 | pipes (@sc{fifo}s) or the @file{/dev/fd} method of naming open files. |
ccc6cda3 JA |
1751 | It takes the form of |
1752 | @example | |
1753 | <(@var{list}) | |
1754 | @end example | |
1755 | @noindent | |
1756 | or | |
1757 | @example | |
1758 | >(@var{list}) | |
1759 | @end example | |
1760 | @noindent | |
1761 | The process @var{list} is run with its input or output connected to a | |
bb70624e | 1762 | @sc{fifo} or some file in @file{/dev/fd}. The name of this file is |
ccc6cda3 JA |
1763 | passed as an argument to the current command as the result of the |
1764 | expansion. If the @code{>(@var{list})} form is used, writing to | |
1765 | the file will provide input for @var{list}. If the | |
1766 | @code{<(@var{list})} form is used, the file passed as an | |
1767 | argument should be read to obtain the output of @var{list}. | |
bb70624e JA |
1768 | Note that no space may appear between the @code{<} or @code{>} |
1769 | and the left parenthesis, otherwise the construct would be interpreted | |
1770 | as a redirection. | |
ccc6cda3 | 1771 | |
cce855bc JA |
1772 | When available, process substitution is performed simultaneously with |
1773 | parameter and variable expansion, command substitution, and arithmetic | |
1774 | expansion. | |
ccc6cda3 JA |
1775 | |
1776 | @node Word Splitting | |
1777 | @subsection Word Splitting | |
1778 | @cindex word splitting | |
1779 | ||
1780 | The shell scans the results of parameter expansion, command substitution, | |
1781 | and arithmetic expansion that did not occur within double quotes for | |
1782 | word splitting. | |
1783 | ||
28ef6c31 | 1784 | The shell treats each character of @env{$IFS} |
ccc6cda3 JA |
1785 | as a delimiter, and splits the results of the other |
1786 | expansions into words on these characters. If | |
28ef6c31 JA |
1787 | @env{IFS} is unset, or its value is exactly @code{<space><tab><newline>}, |
1788 | the default, then any sequence of @env{IFS} | |
1789 | characters serves to delimit words. If @env{IFS} | |
ccc6cda3 JA |
1790 | has a value other than the default, then sequences of |
1791 | the whitespace characters @code{space} and @code{tab} | |
1792 | are ignored at the beginning and end of the | |
1793 | word, as long as the whitespace character is in the | |
28ef6c31 JA |
1794 | value of @env{IFS} (an @env{IFS} whitespace character). |
1795 | Any character in @env{IFS} that is not @env{IFS} | |
1796 | whitespace, along with any adjacent @env{IFS} | |
1797 | whitespace characters, delimits a field. A sequence of @env{IFS} | |
ccc6cda3 | 1798 | whitespace characters is also treated as a delimiter. |
28ef6c31 | 1799 | If the value of @env{IFS} is null, no word splitting occurs. |
ccc6cda3 JA |
1800 | |
1801 | Explicit null arguments (@code{""} or @code{''}) are retained. | |
1802 | Unquoted implicit null arguments, resulting from the expansion of | |
bb70624e | 1803 | parameters that have no values, are removed. |
ccc6cda3 JA |
1804 | If a parameter with no value is expanded within double quotes, a |
1805 | null argument results and is retained. | |
1806 | ||
1807 | Note that if no expansion occurs, no splitting | |
1808 | is performed. | |
1809 | ||
1810 | @node Filename Expansion | |
1811 | @subsection Filename Expansion | |
cce855bc JA |
1812 | @menu |
1813 | * Pattern Matching:: How the shell matches patterns. | |
1814 | @end menu | |
ccc6cda3 JA |
1815 | @cindex expansion, filename |
1816 | @cindex expansion, pathname | |
1817 | @cindex filename expansion | |
1818 | @cindex pathname expansion | |
1819 | ||
28ef6c31 | 1820 | After word splitting, unless the @option{-f} option has been set |
cce855bc | 1821 | (@pxref{The Set Builtin}), Bash scans each word for the characters |
bb70624e | 1822 | @samp{*}, @samp{?}, and @samp{[}. |
ccc6cda3 JA |
1823 | If one of these characters appears, then the word is |
1824 | regarded as a @var{pattern}, | |
1825 | and replaced with an alphabetically sorted list of | |
1826 | file names matching the pattern. If no matching file names are found, | |
1827 | and the shell option @code{nullglob} is disabled, the word is left | |
cce855bc JA |
1828 | unchanged. |
1829 | If the @code{nullglob} option is set, and no matches are found, the word | |
1830 | is removed. | |
b80f6443 JA |
1831 | If the @code{failglob} shell option is set, and no matches are found, |
1832 | an error message is printed and the command is not executed. | |
cce855bc JA |
1833 | If the shell option @code{nocaseglob} is enabled, the match is performed |
1834 | without regard to the case of alphabetic characters. | |
1835 | ||
1836 | When a pattern is used for filename generation, the character @samp{.} | |
ccc6cda3 | 1837 | at the start of a filename or immediately following a slash |
cce855bc JA |
1838 | must be matched explicitly, unless the shell option @code{dotglob} is set. |
1839 | When matching a file name, the slash character must always be | |
1840 | matched explicitly. | |
ccc6cda3 | 1841 | In other cases, the @samp{.} character is not treated specially. |
cce855bc | 1842 | |
ccc6cda3 | 1843 | See the description of @code{shopt} in @ref{Bash Builtins}, |
cce855bc | 1844 | for a description of the @code{nocaseglob}, @code{nullglob}, |
b80f6443 | 1845 | @code{failglob}, and @code{dotglob} options. |
ccc6cda3 | 1846 | |
28ef6c31 | 1847 | The @env{GLOBIGNORE} |
ccc6cda3 | 1848 | shell variable may be used to restrict the set of filenames matching a |
28ef6c31 | 1849 | pattern. If @env{GLOBIGNORE} |
ccc6cda3 | 1850 | is set, each matching filename that also matches one of the patterns in |
28ef6c31 | 1851 | @env{GLOBIGNORE} is removed from the list of matches. The filenames |
ccc6cda3 | 1852 | @file{.} and @file{..} |
b80f6443 JA |
1853 | are always ignored when @env{GLOBIGNORE} |
1854 | is set and not null. | |
1855 | However, setting @env{GLOBIGNORE} to a non-null value has the effect of | |
ccc6cda3 JA |
1856 | enabling the @code{dotglob} |
1857 | shell option, so all other filenames beginning with a | |
1858 | @samp{.} will match. | |
1859 | To get the old behavior of ignoring filenames beginning with a | |
28ef6c31 JA |
1860 | @samp{.}, make @samp{.*} one of the patterns in @env{GLOBIGNORE}. |
1861 | The @code{dotglob} option is disabled when @env{GLOBIGNORE} | |
ccc6cda3 JA |
1862 | is unset. |
1863 | ||
cce855bc JA |
1864 | @node Pattern Matching |
1865 | @subsubsection Pattern Matching | |
1866 | @cindex pattern matching | |
1867 | @cindex matching, pattern | |
1868 | ||
1869 | Any character that appears in a pattern, other than the special pattern | |
b80f6443 JA |
1870 | characters described below, matches itself. |
1871 | The @sc{nul} character may not occur in a pattern. | |
1872 | A backslash escapes the following character; the | |
1873 | escaping backslash is discarded when matching. | |
1874 | The special pattern characters must be quoted if they are to be matched | |
1875 | literally. | |
cce855bc | 1876 | |
ccc6cda3 JA |
1877 | The special pattern characters have the following meanings: |
1878 | @table @code | |
1879 | @item * | |
1880 | Matches any string, including the null string. | |
1881 | @item ? | |
1882 | Matches any single character. | |
1883 | @item [@dots{}] | |
1884 | Matches any one of the enclosed characters. A pair of characters | |
28ef6c31 JA |
1885 | separated by a hyphen denotes a @var{range expression}; |
1886 | any character that sorts between those two characters, inclusive, | |
1887 | using the current locale's collating sequence and character set, | |
ccc6cda3 JA |
1888 | is matched. If the first character following the |
1889 | @samp{[} is a @samp{!} or a @samp{^} | |
1890 | then any character not enclosed is matched. A @samp{@minus{}} | |
1891 | may be matched by including it as the first or last character | |
1892 | in the set. A @samp{]} may be matched by including it as the first | |
1893 | character in the set. | |
28ef6c31 JA |
1894 | The sorting order of characters in range expressions is determined by |
1895 | the current locale and the value of the @env{LC_COLLATE} shell variable, | |
1896 | if set. | |
1897 | ||
1898 | For example, in the default C locale, @samp{[a-dx-z]} is equivalent to | |
1899 | @samp{[abcdxyz]}. Many locales sort characters in dictionary order, and in | |
1900 | these locales @samp{[a-dx-z]} is typically not equivalent to @samp{[abcdxyz]}; | |
1901 | it might be equivalent to @samp{[aBbCcDdxXyYz]}, for example. To obtain | |
1902 | the traditional interpretation of ranges in bracket expressions, you can | |
1903 | force the use of the C locale by setting the @env{LC_COLLATE} or | |
1904 | @env{LC_ALL} environment variable to the value @samp{C}. | |
cce855bc JA |
1905 | |
1906 | Within @samp{[} and @samp{]}, @var{character classes} can be specified | |
1907 | using the syntax | |
1908 | @code{[:}@var{class}@code{:]}, where @var{class} is one of the | |
0628567a | 1909 | following classes defined in the @sc{posix} standard: |
cce855bc JA |
1910 | @example |
1911 | alnum alpha ascii blank cntrl digit graph lower | |
7117c2d2 | 1912 | print punct space upper word xdigit |
cce855bc JA |
1913 | @end example |
1914 | @noindent | |
1915 | A character class matches any character belonging to that class. | |
7117c2d2 JA |
1916 | The @code{word} character class matches letters, digits, and the character |
1917 | @samp{_}. | |
cce855bc JA |
1918 | |
1919 | Within @samp{[} and @samp{]}, an @var{equivalence class} can be | |
1920 | specified using the syntax @code{[=}@var{c}@code{=]}, which | |
1921 | matches all characters with the same collation weight (as defined | |
1922 | by the current locale) as the character @var{c}. | |
1923 | ||
1924 | Within @samp{[} and @samp{]}, the syntax @code{[.}@var{symbol}@code{.]} | |
1925 | matches the collating symbol @var{symbol}. | |
1926 | @end table | |
1927 | ||
1928 | If the @code{extglob} shell option is enabled using the @code{shopt} | |
1929 | builtin, several extended pattern matching operators are recognized. | |
1930 | In the following description, a @var{pattern-list} is a list of one | |
1931 | or more patterns separated by a @samp{|}. | |
1932 | Composite patterns may be formed using one or more of the following | |
1933 | sub-patterns: | |
1934 | ||
1935 | @table @code | |
1936 | @item ?(@var{pattern-list}) | |
1937 | Matches zero or one occurrence of the given patterns. | |
1938 | ||
1939 | @item *(@var{pattern-list}) | |
1940 | Matches zero or more occurrences of the given patterns. | |
1941 | ||
1942 | @item +(@var{pattern-list}) | |
1943 | Matches one or more occurrences of the given patterns. | |
1944 | ||
1945 | @item @@(@var{pattern-list}) | |
95732b49 | 1946 | Matches one of the given patterns. |
cce855bc JA |
1947 | |
1948 | @item !(@var{pattern-list}) | |
1949 | Matches anything except one of the given patterns. | |
ccc6cda3 JA |
1950 | @end table |
1951 | ||
1952 | @node Quote Removal | |
1953 | @subsection Quote Removal | |
1954 | ||
1955 | After the preceding expansions, all unquoted occurrences of the | |
1956 | characters @samp{\}, @samp{'}, and @samp{"} that did not | |
1957 | result from one of the above expansions are removed. | |
1958 | ||
1959 | @node Redirections | |
1960 | @section Redirections | |
1961 | @cindex redirection | |
1962 | ||
1963 | Before a command is executed, its input and output | |
1964 | may be @var{redirected} | |
1965 | using a special notation interpreted by the shell. | |
1966 | Redirection may also be used to open and close files for the | |
1967 | current shell execution environment. The following redirection | |
1968 | operators may precede or appear anywhere within a | |
1969 | simple command or may follow a command. | |
1970 | Redirections are processed in the order they appear, from | |
1971 | left to right. | |
1972 | ||
1973 | In the following descriptions, if the file descriptor number is | |
1974 | omitted, and the first character of the redirection operator is | |
1975 | @samp{<}, the redirection refers to the standard input (file | |
1976 | descriptor 0). If the first character of the redirection operator | |
1977 | is @samp{>}, the redirection refers to the standard output (file | |
1978 | descriptor 1). | |
1979 | ||
cce855bc JA |
1980 | The word following the redirection operator in the following |
1981 | descriptions, unless otherwise noted, is subjected to brace expansion, | |
1982 | tilde expansion, parameter expansion, command substitution, arithmetic | |
bb70624e | 1983 | expansion, quote removal, filename expansion, and word splitting. |
cce855bc | 1984 | If it expands to more than one word, Bash reports an error. |
ccc6cda3 JA |
1985 | |
1986 | Note that the order of redirections is significant. For example, | |
1987 | the command | |
1988 | @example | |
1989 | ls > @var{dirlist} 2>&1 | |
1990 | @end example | |
1991 | @noindent | |
bb70624e JA |
1992 | directs both standard output (file descriptor 1) and standard error |
1993 | (file descriptor 2) to the file @var{dirlist}, while the command | |
ccc6cda3 JA |
1994 | @example |
1995 | ls 2>&1 > @var{dirlist} | |
1996 | @end example | |
1997 | @noindent | |
1998 | directs only the standard output to file @var{dirlist}, | |
1999 | because the standard error was duplicated as standard output | |
2000 | before the standard output was redirected to @var{dirlist}. | |
2001 | ||
bb70624e JA |
2002 | Bash handles several filenames specially when they are used in |
2003 | redirections, as described in the following table: | |
2004 | ||
2005 | @table @code | |
2006 | @item /dev/fd/@var{fd} | |
2007 | If @var{fd} is a valid integer, file descriptor @var{fd} is duplicated. | |
2008 | ||
2009 | @item /dev/stdin | |
2010 | File descriptor 0 is duplicated. | |
2011 | ||
2012 | @item /dev/stdout | |
2013 | File descriptor 1 is duplicated. | |
2014 | ||
2015 | @item /dev/stderr | |
2016 | File descriptor 2 is duplicated. | |
2017 | ||
2018 | @item /dev/tcp/@var{host}/@var{port} | |
2019 | If @var{host} is a valid hostname or Internet address, and @var{port} | |
f73dda09 JA |
2020 | is an integer port number or service name, Bash attempts to open a TCP |
2021 | connection to the corresponding socket. | |
bb70624e JA |
2022 | |
2023 | @item /dev/udp/@var{host}/@var{port} | |
2024 | If @var{host} is a valid hostname or Internet address, and @var{port} | |
f73dda09 JA |
2025 | is an integer port number or service name, Bash attempts to open a UDP |
2026 | connection to the corresponding socket. | |
bb70624e JA |
2027 | |
2028 | @end table | |
2029 | ||
cce855bc JA |
2030 | A failure to open or create a file causes the redirection to fail. |
2031 | ||
95732b49 JA |
2032 | Redirections using file descriptors greater than 9 should be used with |
2033 | care, as they may conflict with file descriptors the shell uses | |
2034 | internally. | |
2035 | ||
ccc6cda3 JA |
2036 | @subsection Redirecting Input |
2037 | Redirection of input causes the file whose name results from | |
2038 | the expansion of @var{word} | |
2039 | to be opened for reading on file descriptor @code{n}, | |
2040 | or the standard input (file descriptor 0) if @code{n} | |
2041 | is not specified. | |
2042 | ||
2043 | The general format for redirecting input is: | |
2044 | @example | |
7117c2d2 | 2045 | [@var{n}]<@var{word} |
ccc6cda3 JA |
2046 | @end example |
2047 | ||
2048 | @subsection Redirecting Output | |
2049 | Redirection of output causes the file whose name results from | |
2050 | the expansion of @var{word} | |
7117c2d2 JA |
2051 | to be opened for writing on file descriptor @var{n}, |
2052 | or the standard output (file descriptor 1) if @var{n} | |
ccc6cda3 JA |
2053 | is not specified. If the file does not exist it is created; |
2054 | if it does exist it is truncated to zero size. | |
2055 | ||
2056 | The general format for redirecting output is: | |
2057 | @example | |
7117c2d2 | 2058 | [@var{n}]>[|]@var{word} |
ccc6cda3 JA |
2059 | @end example |
2060 | ||
cce855bc JA |
2061 | If the redirection operator is @samp{>}, and the @code{noclobber} |
2062 | option to the @code{set} builtin has been enabled, the redirection | |
bb70624e | 2063 | will fail if the file whose name results from the expansion of |
cce855bc JA |
2064 | @var{word} exists and is a regular file. |
2065 | If the redirection operator is @samp{>|}, or the redirection operator is | |
2066 | @samp{>} and the @code{noclobber} option is not enabled, the redirection | |
2067 | is attempted even if the file named by @var{word} exists. | |
ccc6cda3 JA |
2068 | |
2069 | @subsection Appending Redirected Output | |
2070 | Redirection of output in this fashion | |
2071 | causes the file whose name results from | |
2072 | the expansion of @var{word} | |
7117c2d2 JA |
2073 | to be opened for appending on file descriptor @var{n}, |
2074 | or the standard output (file descriptor 1) if @var{n} | |
ccc6cda3 JA |
2075 | is not specified. If the file does not exist it is created. |
2076 | ||
2077 | The general format for appending output is: | |
2078 | @example | |
7117c2d2 | 2079 | [@var{n}]>>@var{word} |
ccc6cda3 JA |
2080 | @end example |
2081 | ||
2082 | @subsection Redirecting Standard Output and Standard Error | |
2083 | Bash allows both the | |
2084 | standard output (file descriptor 1) and | |
2085 | the standard error output (file descriptor 2) | |
2086 | to be redirected to the file whose name is the | |
2087 | expansion of @var{word} with this construct. | |
2088 | ||
2089 | There are two formats for redirecting standard output and | |
2090 | standard error: | |
2091 | @example | |
2092 | &>@var{word} | |
2093 | @end example | |
2094 | @noindent | |
2095 | and | |
2096 | @example | |
2097 | >&@var{word} | |
2098 | @end example | |
2099 | @noindent | |
2100 | Of the two forms, the first is preferred. | |
2101 | This is semantically equivalent to | |
2102 | @example | |
2103 | >@var{word} 2>&1 | |
2104 | @end example | |
2105 | ||
2106 | @subsection Here Documents | |
2107 | This type of redirection instructs the shell to read input from the | |
2108 | current source until a line containing only @var{word} | |
2109 | (with no trailing blanks) is seen. All of | |
2110 | the lines read up to that point are then used as the standard | |
2111 | input for a command. | |
2112 | ||
7117c2d2 | 2113 | The format of here-documents is: |
ccc6cda3 JA |
2114 | @example |
2115 | <<[@minus{}]@var{word} | |
2116 | @var{here-document} | |
2117 | @var{delimiter} | |
2118 | @end example | |
2119 | ||
bb70624e JA |
2120 | No parameter expansion, command substitution, arithmetic expansion, |
2121 | or filename expansion is performed on | |
ccc6cda3 JA |
2122 | @var{word}. If any characters in @var{word} are quoted, the |
2123 | @var{delimiter} is the result of quote removal on @var{word}, | |
cce855bc JA |
2124 | and the lines in the here-document are not expanded. |
2125 | If @var{word} is unquoted, | |
ccc6cda3 JA |
2126 | all lines of the here-document are subjected to parameter expansion, |
2127 | command substitution, and arithmetic expansion. In the latter | |
bb70624e | 2128 | case, the character sequence @code{\newline} is ignored, and @samp{\} |
ccc6cda3 JA |
2129 | must be used to quote the characters |
2130 | @samp{\}, @samp{$}, and @samp{`}. | |
2131 | ||
2132 | If the redirection operator is @samp{<<-}, | |
2133 | then all leading tab characters are stripped from input lines and the | |
2134 | line containing @var{delimiter}. | |
2135 | This allows here-documents within shell scripts to be indented in a | |
2136 | natural fashion. | |
2137 | ||
7117c2d2 JA |
2138 | @subsection Here Strings |
2139 | A variant of here documents, the format is: | |
2140 | @example | |
2141 | <<< @var{word} | |
2142 | @end example | |
2143 | ||
2144 | The @var{word} is expanded and supplied to the command on its standard | |
2145 | input. | |
2146 | ||
ccc6cda3 JA |
2147 | @subsection Duplicating File Descriptors |
2148 | The redirection operator | |
2149 | @example | |
7117c2d2 | 2150 | [@var{n}]<&@var{word} |
ccc6cda3 JA |
2151 | @end example |
2152 | @noindent | |
2153 | is used to duplicate input file descriptors. | |
2154 | If @var{word} | |
7117c2d2 | 2155 | expands to one or more digits, the file descriptor denoted by @var{n} |
cce855bc JA |
2156 | is made to be a copy of that file descriptor. |
2157 | If the digits in @var{word} do not specify a file descriptor open for | |
2158 | input, a redirection error occurs. | |
2159 | If @var{word} | |
7117c2d2 JA |
2160 | evaluates to @samp{-}, file descriptor @var{n} is closed. If |
2161 | @var{n} is not specified, the standard input (file descriptor 0) is used. | |
ccc6cda3 JA |
2162 | |
2163 | The operator | |
2164 | @example | |
7117c2d2 | 2165 | [@var{n}]>&@var{word} |
ccc6cda3 JA |
2166 | @end example |
2167 | @noindent | |
2168 | is used similarly to duplicate output file descriptors. If | |
7117c2d2 | 2169 | @var{n} is not specified, the standard output (file descriptor 1) is used. |
cce855bc JA |
2170 | If the digits in @var{word} do not specify a file descriptor open for |
2171 | output, a redirection error occurs. | |
7117c2d2 | 2172 | As a special case, if @var{n} is omitted, and @var{word} does not |
ccc6cda3 JA |
2173 | expand to one or more digits, the standard output and standard |
2174 | error are redirected as described previously. | |
2175 | ||
7117c2d2 JA |
2176 | @subsection Moving File Descriptors |
2177 | The redirection operator | |
2178 | @example | |
2179 | [@var{n}]<&@var{digit}- | |
2180 | @end example | |
2181 | @noindent | |
2182 | moves the file descriptor @var{digit} to file descriptor @var{n}, | |
2183 | or the standard input (file descriptor 0) if @var{n} is not specified. | |
2184 | @var{digit} is closed after being duplicated to @var{n}. | |
2185 | ||
2186 | Similarly, the redirection operator | |
2187 | @example | |
2188 | [@var{n}]>&@var{digit}- | |
2189 | @end example | |
2190 | @noindent | |
2191 | moves the file descriptor @var{digit} to file descriptor @var{n}, | |
2192 | or the standard output (file descriptor 1) if @var{n} is not specified. | |
2193 | ||
ccc6cda3 JA |
2194 | @subsection Opening File Descriptors for Reading and Writing |
2195 | The redirection operator | |
2196 | @example | |
7117c2d2 | 2197 | [@var{n}]<>@var{word} |
ccc6cda3 JA |
2198 | @end example |
2199 | @noindent | |
2200 | causes the file whose name is the expansion of @var{word} | |
2201 | to be opened for both reading and writing on file descriptor | |
7117c2d2 | 2202 | @var{n}, or on file descriptor 0 if @var{n} |
ccc6cda3 JA |
2203 | is not specified. If the file does not exist, it is created. |
2204 | ||
2205 | @node Executing Commands | |
2206 | @section Executing Commands | |
2207 | ||
2208 | @menu | |
cce855bc JA |
2209 | * Simple Command Expansion:: How Bash expands simple commands before |
2210 | executing them. | |
ccc6cda3 | 2211 | * Command Search and Execution:: How Bash finds commands and runs them. |
cce855bc JA |
2212 | * Command Execution Environment:: The environment in which Bash |
2213 | executes commands that are not | |
2214 | shell builtins. | |
ccc6cda3 | 2215 | * Environment:: The environment given to a command. |
ccc6cda3 JA |
2216 | * Exit Status:: The status returned by commands and how Bash |
2217 | interprets it. | |
ccc6cda3 JA |
2218 | * Signals:: What happens when Bash or a command it runs |
2219 | receives a signal. | |
2220 | @end menu | |
2221 | ||
cce855bc JA |
2222 | @node Simple Command Expansion |
2223 | @subsection Simple Command Expansion | |
2224 | @cindex command expansion | |
2225 | ||
2226 | When a simple command is executed, the shell performs the following | |
2227 | expansions, assignments, and redirections, from left to right. | |
2228 | ||
2229 | @enumerate | |
2230 | @item | |
2231 | The words that the parser has marked as variable assignments (those | |
2232 | preceding the command name) and redirections are saved for later | |
2233 | processing. | |
2234 | ||
2235 | @item | |
2236 | The words that are not variable assignments or redirections are | |
2237 | expanded (@pxref{Shell Expansions}). | |
2238 | If any words remain after expansion, the first word | |
2239 | is taken to be the name of the command and the remaining words are | |
2240 | the arguments. | |
2241 | ||
2242 | @item | |
2243 | Redirections are performed as described above (@pxref{Redirections}). | |
2244 | ||
2245 | @item | |
2246 | The text after the @samp{=} in each variable assignment undergoes tilde | |
2247 | expansion, parameter expansion, command substitution, arithmetic expansion, | |
2248 | and quote removal before being assigned to the variable. | |
2249 | @end enumerate | |
2250 | ||
2251 | If no command name results, the variable assignments affect the current | |
2252 | shell environment. Otherwise, the variables are added to the environment | |
2253 | of the executed command and do not affect the current shell environment. | |
2254 | If any of the assignments attempts to assign a value to a readonly variable, | |
2255 | an error occurs, and the command exits with a non-zero status. | |
2256 | ||
2257 | If no command name results, redirections are performed, but do not | |
2258 | affect the current shell environment. A redirection error causes the | |
2259 | command to exit with a non-zero status. | |
2260 | ||
2261 | If there is a command name left after expansion, execution proceeds as | |
2262 | described below. Otherwise, the command exits. If one of the expansions | |
2263 | contained a command substitution, the exit status of the command is | |
2264 | the exit status of the last command substitution performed. If there | |
2265 | were no command substitutions, the command exits with a status of zero. | |
2266 | ||
ccc6cda3 JA |
2267 | @node Command Search and Execution |
2268 | @subsection Command Search and Execution | |
2269 | @cindex command execution | |
2270 | @cindex command search | |
2271 | ||
2272 | After a command has been split into words, if it results in a | |
2273 | simple command and an optional list of arguments, the following | |
2274 | actions are taken. | |
2275 | ||
2276 | @enumerate | |
2277 | @item | |
2278 | If the command name contains no slashes, the shell attempts to | |
2279 | locate it. If there exists a shell function by that name, that | |
bb70624e | 2280 | function is invoked as described in @ref{Shell Functions}. |
ccc6cda3 JA |
2281 | |
2282 | @item | |
2283 | If the name does not match a function, the shell searches for | |
2284 | it in the list of shell builtins. If a match is found, that | |
2285 | builtin is invoked. | |
2286 | ||
2287 | @item | |
2288 | If the name is neither a shell function nor a builtin, | |
2289 | and contains no slashes, Bash searches each element of | |
28ef6c31 | 2290 | @env{$PATH} for a directory containing an executable file |
ccc6cda3 | 2291 | by that name. Bash uses a hash table to remember the full |
28ef6c31 | 2292 | pathnames of executable files to avoid multiple @env{PATH} searches |
cce855bc | 2293 | (see the description of @code{hash} in @ref{Bourne Shell Builtins}). |
28ef6c31 | 2294 | A full search of the directories in @env{$PATH} |
ccc6cda3 JA |
2295 | is performed only if the command is not found in the hash table. |
2296 | If the search is unsuccessful, the shell prints an error | |
cce855bc | 2297 | message and returns an exit status of 127. |
ccc6cda3 JA |
2298 | |
2299 | @item | |
2300 | If the search is successful, or if the command name contains | |
cce855bc JA |
2301 | one or more slashes, the shell executes the named program in |
2302 | a separate execution environment. | |
ccc6cda3 JA |
2303 | Argument 0 is set to the name given, and the remaining arguments |
2304 | to the command are set to the arguments supplied, if any. | |
2305 | ||
2306 | @item | |
2307 | If this execution fails because the file is not in executable | |
cce855bc JA |
2308 | format, and the file is not a directory, it is assumed to be a |
2309 | @var{shell script} and the shell executes it as described in | |
2310 | @ref{Shell Scripts}. | |
2311 | ||
2312 | @item | |
2313 | If the command was not begun asynchronously, the shell waits for | |
2314 | the command to complete and collects its exit status. | |
2315 | ||
ccc6cda3 JA |
2316 | @end enumerate |
2317 | ||
cce855bc JA |
2318 | @node Command Execution Environment |
2319 | @subsection Command Execution Environment | |
2320 | @cindex execution environment | |
2321 | ||
2322 | The shell has an @var{execution environment}, which consists of the | |
2323 | following: | |
2324 | ||
2325 | @itemize @bullet | |
2326 | @item | |
2327 | open files inherited by the shell at invocation, as modified by | |
2328 | redirections supplied to the @code{exec} builtin | |
2329 | ||
2330 | @item | |
2331 | the current working directory as set by @code{cd}, @code{pushd}, or | |
2332 | @code{popd}, or inherited by the shell at invocation | |
2333 | ||
2334 | @item | |
2335 | the file creation mode mask as set by @code{umask} or inherited from | |
2336 | the shell's parent | |
2337 | ||
2338 | @item | |
2339 | current traps set by @code{trap} | |
2340 | ||
2341 | @item | |
2342 | shell parameters that are set by variable assignment or with @code{set} | |
2343 | or inherited from the shell's parent in the environment | |
2344 | ||
2345 | @item | |
2346 | shell functions defined during execution or inherited from the shell's | |
2347 | parent in the environment | |
2348 | ||
2349 | @item | |
2350 | options enabled at invocation (either by default or with command-line | |
2351 | arguments) or by @code{set} | |
2352 | ||
2353 | @item | |
2354 | options enabled by @code{shopt} | |
2355 | ||
2356 | @item | |
2357 | shell aliases defined with @code{alias} (@pxref{Aliases}) | |
2358 | ||
2359 | @item | |
bb70624e | 2360 | various process @sc{id}s, including those of background jobs |
cce855bc | 2361 | (@pxref{Lists}), the value of @code{$$}, and the value of |
28ef6c31 | 2362 | @env{$PPID} |
cce855bc JA |
2363 | |
2364 | @end itemize | |
2365 | ||
2366 | When a simple command other than a builtin or shell function | |
2367 | is to be executed, it | |
2368 | is invoked in a separate execution environment that consists of | |
2369 | the following. Unless otherwise noted, the values are inherited | |
2370 | from the shell. | |
2371 | ||
2372 | @itemize @bullet | |
2373 | @item | |
2374 | the shell's open files, plus any modifications and additions specified | |
2375 | by redirections to the command | |
2376 | ||
2377 | @item | |
2378 | the current working directory | |
2379 | ||
2380 | @item | |
2381 | the file creation mode mask | |
2382 | ||
2383 | @item | |
b80f6443 JA |
2384 | shell variables and functions marked for export, along with variables |
2385 | exported for the command, passed in the environment (@pxref{Environment}) | |
cce855bc JA |
2386 | |
2387 | @item | |
2388 | traps caught by the shell are reset to the values inherited from the | |
2389 | shell's parent, and traps ignored by the shell are ignored | |
2390 | ||
2391 | @end itemize | |
2392 | ||
2393 | A command invoked in this separate environment cannot affect the | |
2394 | shell's execution environment. | |
2395 | ||
b80f6443 JA |
2396 | Command substitution, commands grouped with parentheses, |
2397 | and asynchronous commands are invoked in a | |
cce855bc JA |
2398 | subshell environment that is a duplicate of the shell environment, |
2399 | except that traps caught by the shell are reset to the values | |
2400 | that the shell inherited from its parent at invocation. Builtin | |
2401 | commands that are invoked as part of a pipeline are also executed | |
2402 | in a subshell environment. Changes made to the subshell environment | |
2403 | cannot affect the shell's execution environment. | |
2404 | ||
f73dda09 JA |
2405 | If a command is followed by a @samp{&} and job control is not active, the |
2406 | default standard input for the command is the empty file @file{/dev/null}. | |
2407 | Otherwise, the invoked command inherits the file descriptors of the calling | |
2408 | shell as modified by redirections. | |
2409 | ||
ccc6cda3 JA |
2410 | @node Environment |
2411 | @subsection Environment | |
2412 | @cindex environment | |
2413 | ||
2414 | When a program is invoked it is given an array of strings | |
2415 | called the @var{environment}. | |
2416 | This is a list of name-value pairs, of the form @code{name=value}. | |
2417 | ||
bb70624e JA |
2418 | Bash provides several ways to manipulate the environment. |
2419 | On invocation, the shell scans its own environment and | |
ccc6cda3 JA |
2420 | creates a parameter for each name found, automatically marking |
2421 | it for @var{export} | |
2422 | to child processes. Executed commands inherit the environment. | |
2423 | The @code{export} and @samp{declare -x} | |
2424 | commands allow parameters and functions to be added to and | |
2425 | deleted from the environment. If the value of a parameter | |
2426 | in the environment is modified, the new value becomes part | |
2427 | of the environment, replacing the old. The environment | |
2428 | inherited by any executed command consists of the shell's | |
2429 | initial environment, whose values may be modified in the shell, | |
cce855bc JA |
2430 | less any pairs removed by the @code{unset} and @samp{export -n} |
2431 | commands, plus any additions via the @code{export} and | |
2432 | @samp{declare -x} commands. | |
ccc6cda3 JA |
2433 | |
2434 | The environment for any simple command | |
2435 | or function may be augmented temporarily by prefixing it with | |
2436 | parameter assignments, as described in @ref{Shell Parameters}. | |
2437 | These assignment statements affect only the environment seen | |
2438 | by that command. | |
2439 | ||
28ef6c31 | 2440 | If the @option{-k} option is set (@pxref{The Set Builtin}), then all |
ccc6cda3 JA |
2441 | parameter assignments are placed in the environment for a command, |
2442 | not just those that precede the command name. | |
2443 | ||
2444 | When Bash invokes an external command, the variable @samp{$_} | |
2445 | is set to the full path name of the command and passed to that | |
2446 | command in its environment. | |
2447 | ||
2448 | @node Exit Status | |
2449 | @subsection Exit Status | |
2450 | @cindex exit status | |
2451 | ||
cce855bc | 2452 | For the shell's purposes, a command which exits with a |
ccc6cda3 JA |
2453 | zero exit status has succeeded. |
2454 | A non-zero exit status indicates failure. | |
2455 | This seemingly counter-intuitive scheme is used so there | |
2456 | is one well-defined way to indicate success and a variety of | |
2457 | ways to indicate various failure modes. | |
bb70624e JA |
2458 | When a command terminates on a fatal signal whose number is @var{N}, |
2459 | Bash uses the value 128+@var{N} as the exit status. | |
ccc6cda3 JA |
2460 | |
2461 | If a command is not found, the child process created to | |
2462 | execute it returns a status of 127. If a command is found | |
2463 | but is not executable, the return status is 126. | |
2464 | ||
cce855bc JA |
2465 | If a command fails because of an error during expansion or redirection, |
2466 | the exit status is greater than zero. | |
2467 | ||
ccc6cda3 JA |
2468 | The exit status is used by the Bash conditional commands |
2469 | (@pxref{Conditional Constructs}) and some of the list | |
2470 | constructs (@pxref{Lists}). | |
2471 | ||
2472 | All of the Bash builtins return an exit status of zero if they succeed | |
2473 | and a non-zero status on failure, so they may be used by the | |
2474 | conditional and list constructs. | |
cce855bc | 2475 | All builtins return an exit status of 2 to indicate incorrect usage. |
ccc6cda3 JA |
2476 | |
2477 | @node Signals | |
2478 | @subsection Signals | |
2479 | @cindex signal handling | |
2480 | ||
cce855bc | 2481 | When Bash is interactive, in the absence of any traps, it ignores |
ccc6cda3 JA |
2482 | @code{SIGTERM} (so that @samp{kill 0} does not kill an interactive shell), |
2483 | and @code{SIGINT} | |
2484 | is caught and handled (so that the @code{wait} builtin is interruptible). | |
2485 | When Bash receives a @code{SIGINT}, it breaks out of any executing loops. | |
2486 | In all cases, Bash ignores @code{SIGQUIT}. | |
2487 | If job control is in effect (@pxref{Job Control}), Bash | |
2488 | ignores @code{SIGTTIN}, @code{SIGTTOU}, and @code{SIGTSTP}. | |
2489 | ||
b80f6443 | 2490 | Non-builtin commands started by Bash have signal handlers set to the |
cce855bc JA |
2491 | values inherited by the shell from its parent. |
2492 | When job control is not in effect, asynchronous commands | |
b80f6443 JA |
2493 | ignore @code{SIGINT} and @code{SIGQUIT} in addition to these inherited |
2494 | handlers. | |
cce855bc JA |
2495 | Commands run as a result of |
2496 | command substitution ignore the keyboard-generated job control signals | |
ccc6cda3 JA |
2497 | @code{SIGTTIN}, @code{SIGTTOU}, and @code{SIGTSTP}. |
2498 | ||
2499 | The shell exits by default upon receipt of a @code{SIGHUP}. | |
f73dda09 JA |
2500 | Before exiting, an interactive shell resends the @code{SIGHUP} to |
2501 | all jobs, running or stopped. | |
cce855bc JA |
2502 | Stopped jobs are sent @code{SIGCONT} to ensure that they receive |
2503 | the @code{SIGHUP}. | |
2504 | To prevent the shell from sending the @code{SIGHUP} signal to a | |
2505 | particular job, it should be removed | |
2506 | from the jobs table with the @code{disown} | |
2507 | builtin (@pxref{Job Control Builtins}) or marked | |
2508 | to not receive @code{SIGHUP} using @code{disown -h}. | |
2509 | ||
2510 | If the @code{huponexit} shell option has been set with @code{shopt} | |
2511 | (@pxref{Bash Builtins}), Bash sends a @code{SIGHUP} to all jobs when | |
2512 | an interactive login shell exits. | |
2513 | ||
b80f6443 JA |
2514 | If Bash is waiting for a command to complete and receives a signal |
2515 | for which a trap has been set, the trap will not be executed until | |
2516 | the command completes. | |
cce855bc JA |
2517 | When Bash is waiting for an asynchronous |
2518 | command via the @code{wait} builtin, the reception of a signal for | |
2519 | which a trap has been set will cause the @code{wait} builtin to return | |
2520 | immediately with an exit status greater than 128, immediately after | |
2521 | which the trap is executed. | |
ccc6cda3 JA |
2522 | |
2523 | @node Shell Scripts | |
2524 | @section Shell Scripts | |
2525 | @cindex shell script | |
2526 | ||
2527 | A shell script is a text file containing shell commands. When such | |
2528 | a file is used as the first non-option argument when invoking Bash, | |
28ef6c31 | 2529 | and neither the @option{-c} nor @option{-s} option is supplied |
ccc6cda3 JA |
2530 | (@pxref{Invoking Bash}), |
2531 | Bash reads and executes commands from the file, then exits. This | |
f73dda09 JA |
2532 | mode of operation creates a non-interactive shell. The shell first |
2533 | searches for the file in the current directory, and looks in the | |
2534 | directories in @env{$PATH} if not found there. | |
2535 | ||
2536 | When Bash runs | |
ccc6cda3 JA |
2537 | a shell script, it sets the special parameter @code{0} to the name |
2538 | of the file, rather than the name of the shell, and the positional | |
2539 | parameters are set to the remaining arguments, if any are given. | |
2540 | If no additional arguments are supplied, the positional parameters | |
2541 | are unset. | |
2542 | ||
2543 | A shell script may be made executable by using the @code{chmod} command | |
2544 | to turn on the execute bit. When Bash finds such a file while | |
28ef6c31 | 2545 | searching the @env{$PATH} for a command, it spawns a subshell to |
ccc6cda3 JA |
2546 | execute it. In other words, executing |
2547 | @example | |
2548 | filename @var{arguments} | |
2549 | @end example | |
2550 | @noindent | |
2551 | is equivalent to executing | |
2552 | @example | |
2553 | bash filename @var{arguments} | |
2554 | @end example | |
2555 | ||
2556 | @noindent | |
2557 | if @code{filename} is an executable shell script. | |
2558 | This subshell reinitializes itself, so that the effect is as if a | |
cce855bc JA |
2559 | new shell had been invoked to interpret the script, with the |
2560 | exception that the locations of commands remembered by the parent | |
2561 | (see the description of @code{hash} in @ref{Bourne Shell Builtins}) | |
2562 | are retained by the child. | |
ccc6cda3 | 2563 | |
bb70624e | 2564 | Most versions of Unix make this a part of the operating system's command |
ccc6cda3 JA |
2565 | execution mechanism. If the first line of a script begins with |
2566 | the two characters @samp{#!}, the remainder of the line specifies | |
bb70624e JA |
2567 | an interpreter for the program. |
2568 | Thus, you can specify Bash, @code{awk}, Perl, or some other | |
2569 | interpreter and write the rest of the script file in that language. | |
2570 | ||
2571 | The arguments to the interpreter | |
ccc6cda3 JA |
2572 | consist of a single optional argument following the interpreter |
2573 | name on the first line of the script file, followed by the name of | |
2574 | the script file, followed by the rest of the arguments. Bash | |
2575 | will perform this action on operating systems that do not handle it | |
2576 | themselves. Note that some older versions of Unix limit the interpreter | |
2577 | name and argument to a maximum of 32 characters. | |
2578 | ||
bb70624e JA |
2579 | Bash scripts often begin with @code{#! /bin/bash} (assuming that |
2580 | Bash has been installed in @file{/bin}), since this ensures that | |
2581 | Bash will be used to interpret the script, even if it is executed | |
2582 | under another shell. | |
2583 | ||
2584 | @node Shell Builtin Commands | |
2585 | @chapter Shell Builtin Commands | |
ccc6cda3 JA |
2586 | |
2587 | @menu | |
2588 | * Bourne Shell Builtins:: Builtin commands inherited from the Bourne | |
2589 | Shell. | |
bb70624e JA |
2590 | * Bash Builtins:: Table of builtins specific to Bash. |
2591 | * The Set Builtin:: This builtin is so overloaded it | |
2592 | deserves its own section. | |
2593 | * Special Builtins:: Builtin commands classified specially by | |
0628567a | 2594 | POSIX. |
ccc6cda3 JA |
2595 | @end menu |
2596 | ||
bb70624e JA |
2597 | Builtin commands are contained within the shell itself. |
2598 | When the name of a builtin command is used as the first word of | |
2599 | a simple command (@pxref{Simple Commands}), the shell executes | |
2600 | the command directly, without invoking another program. | |
2601 | Builtin commands are necessary to implement functionality impossible | |
2602 | or inconvenient to obtain with separate utilities. | |
2603 | ||
0628567a | 2604 | This section briefly describes the builtins which Bash inherits from |
bb70624e JA |
2605 | the Bourne Shell, as well as the builtin commands which are unique |
2606 | to or have been extended in Bash. | |
2607 | ||
2608 | Several builtin commands are described in other chapters: builtin | |
2609 | commands which provide the Bash interface to the job control | |
2610 | facilities (@pxref{Job Control Builtins}), the directory stack | |
2611 | (@pxref{Directory Stack Builtins}), the command history | |
2612 | (@pxref{Bash History Builtins}), and the programmable completion | |
2613 | facilities (@pxref{Programmable Completion Builtins}). | |
2614 | ||
2615 | Many of the builtins have been extended by @sc{posix} or Bash. | |
ccc6cda3 | 2616 | |
b80f6443 JA |
2617 | Unless otherwise noted, each builtin command documented as accepting |
2618 | options preceded by @samp{-} accepts @samp{--} | |
2619 | to signify the end of the options. | |
95732b49 JA |
2620 | For example, the @code{:}, @code{true}, @code{false}, and @code{test} |
2621 | builtins do not accept options. | |
b80f6443 | 2622 | |
ccc6cda3 JA |
2623 | @node Bourne Shell Builtins |
2624 | @section Bourne Shell Builtins | |
2625 | ||
bb70624e | 2626 | The following shell builtin commands are inherited from the Bourne Shell. |
0628567a | 2627 | These commands are implemented as specified by the @sc{posix} standard. |
ccc6cda3 JA |
2628 | |
2629 | @table @code | |
bb70624e | 2630 | @item : @r{(a colon)} |
ccc6cda3 JA |
2631 | @btindex : |
2632 | @example | |
2633 | : [@var{arguments}] | |
2634 | @end example | |
2635 | Do nothing beyond expanding @var{arguments} and performing redirections. | |
cce855bc | 2636 | The return status is zero. |
ccc6cda3 | 2637 | |
bb70624e | 2638 | @item . @r{(a period)} |
ccc6cda3 JA |
2639 | @btindex . |
2640 | @example | |
b72432fd | 2641 | . @var{filename} [@var{arguments}] |
ccc6cda3 JA |
2642 | @end example |
2643 | Read and execute commands from the @var{filename} argument in the | |
cce855bc | 2644 | current shell context. If @var{filename} does not contain a slash, |
28ef6c31 JA |
2645 | the @env{PATH} variable is used to find @var{filename}. |
2646 | When Bash is not in @sc{posix} mode, the current directory is searched | |
2647 | if @var{filename} is not found in @env{$PATH}. | |
b72432fd JA |
2648 | If any @var{arguments} are supplied, they become the positional |
2649 | parameters when @var{filename} is executed. Otherwise the positional | |
2650 | parameters are unchanged. | |
cce855bc JA |
2651 | The return status is the exit status of the last command executed, or |
2652 | zero if no commands are executed. If @var{filename} is not found, or | |
2653 | cannot be read, the return status is non-zero. | |
bb70624e | 2654 | This builtin is equivalent to @code{source}. |
ccc6cda3 JA |
2655 | |
2656 | @item break | |
2657 | @btindex break | |
2658 | @example | |
2659 | break [@var{n}] | |
2660 | @end example | |
2661 | Exit from a @code{for}, @code{while}, @code{until}, or @code{select} loop. | |
2662 | If @var{n} is supplied, the @var{n}th enclosing loop is exited. | |
cce855bc JA |
2663 | @var{n} must be greater than or equal to 1. |
2664 | The return status is zero unless @var{n} is not greater than or equal to 1. | |
ccc6cda3 JA |
2665 | |
2666 | @item cd | |
2667 | @btindex cd | |
2668 | @example | |
7117c2d2 | 2669 | cd [-L|-P] [@var{directory}] |
ccc6cda3 | 2670 | @end example |
b80f6443 JA |
2671 | Change the current working directory to @var{directory}. |
2672 | If @var{directory} is not given, the value of the @env{HOME} shell | |
2673 | variable is used. | |
2674 | If the shell variable @env{CDPATH} exists, it is used as a search path. | |
2675 | If @var{directory} begins with a slash, @env{CDPATH} is not used. | |
2676 | ||
2677 | The @option{-P} option means to not follow symbolic links; symbolic | |
2678 | links are followed by default or with the @option{-L} option. | |
28ef6c31 | 2679 | If @var{directory} is @samp{-}, it is equivalent to @env{$OLDPWD}. |
b80f6443 JA |
2680 | |
2681 | If a non-empty directory name from @env{CDPATH} is used, or if | |
2682 | @samp{-} is the first argument, and the directory change is | |
2683 | successful, the absolute pathname of the new working directory is | |
2684 | written to the standard output. | |
2685 | ||
cce855bc JA |
2686 | The return status is zero if the directory is successfully changed, |
2687 | non-zero otherwise. | |
ccc6cda3 JA |
2688 | |
2689 | @item continue | |
2690 | @btindex continue | |
2691 | @example | |
2692 | continue [@var{n}] | |
2693 | @end example | |
2694 | Resume the next iteration of an enclosing @code{for}, @code{while}, | |
2695 | @code{until}, or @code{select} loop. | |
cce855bc JA |
2696 | If @var{n} is supplied, the execution of the @var{n}th enclosing loop |
2697 | is resumed. | |
2698 | @var{n} must be greater than or equal to 1. | |
2699 | The return status is zero unless @var{n} is not greater than or equal to 1. | |
ccc6cda3 JA |
2700 | |
2701 | @item eval | |
2702 | @btindex eval | |
2703 | @example | |
2704 | eval [@var{arguments}] | |
2705 | @end example | |
cce855bc JA |
2706 | The arguments are concatenated together into a single command, which is |
2707 | then read and executed, and its exit status returned as the exit status | |
2708 | of @code{eval}. | |
2709 | If there are no arguments or only empty arguments, the return status is | |
2710 | zero. | |
ccc6cda3 JA |
2711 | |
2712 | @item exec | |
2713 | @btindex exec | |
2714 | @example | |
cce855bc | 2715 | exec [-cl] [-a @var{name}] [@var{command} [@var{arguments}]] |
ccc6cda3 JA |
2716 | @end example |
2717 | If @var{command} | |
cce855bc | 2718 | is supplied, it replaces the shell without creating a new process. |
28ef6c31 | 2719 | If the @option{-l} option is supplied, the shell places a dash at the |
bb70624e | 2720 | beginning of the zeroth arg passed to @var{command}. |
ccc6cda3 | 2721 | This is what the @code{login} program does. |
28ef6c31 | 2722 | The @option{-c} option causes @var{command} to be executed with an empty |
cce855bc | 2723 | environment. |
28ef6c31 | 2724 | If @option{-a} is supplied, the shell passes @var{name} as the zeroth |
cce855bc | 2725 | argument to @var{command}. |
ccc6cda3 | 2726 | If no @var{command} is specified, redirections may be used to affect |
cce855bc JA |
2727 | the current shell environment. If there are no redirection errors, the |
2728 | return status is zero; otherwise the return status is non-zero. | |
ccc6cda3 JA |
2729 | |
2730 | @item exit | |
2731 | @btindex exit | |
2732 | @example | |
2733 | exit [@var{n}] | |
2734 | @end example | |
2735 | Exit the shell, returning a status of @var{n} to the shell's parent. | |
bb70624e | 2736 | If @var{n} is omitted, the exit status is that of the last command executed. |
cce855bc | 2737 | Any trap on @code{EXIT} is executed before the shell terminates. |
ccc6cda3 JA |
2738 | |
2739 | @item export | |
2740 | @btindex export | |
2741 | @example | |
2742 | export [-fn] [-p] [@var{name}[=@var{value}]] | |
2743 | @end example | |
2744 | Mark each @var{name} to be passed to child processes | |
28ef6c31 | 2745 | in the environment. If the @option{-f} option is supplied, the @var{name}s |
cce855bc | 2746 | refer to shell functions; otherwise the names refer to shell variables. |
28ef6c31 JA |
2747 | The @option{-n} option means to no longer mark each @var{name} for export. |
2748 | If no @var{names} are supplied, or if the @option{-p} option is given, a | |
ccc6cda3 | 2749 | list of exported names is displayed. |
28ef6c31 | 2750 | The @option{-p} option displays output in a form that may be reused as input. |
b80f6443 JA |
2751 | If a variable name is followed by =@var{value}, the value of |
2752 | the variable is set to @var{value}. | |
2753 | ||
cce855bc | 2754 | The return status is zero unless an invalid option is supplied, one of |
28ef6c31 | 2755 | the names is not a valid shell variable name, or @option{-f} is supplied |
cce855bc | 2756 | with a name that is not a shell function. |
ccc6cda3 JA |
2757 | |
2758 | @item getopts | |
2759 | @btindex getopts | |
2760 | @example | |
2761 | getopts @var{optstring} @var{name} [@var{args}] | |
2762 | @end example | |
2763 | @code{getopts} is used by shell scripts to parse positional parameters. | |
bb70624e JA |
2764 | @var{optstring} contains the option characters to be recognized; if a |
2765 | character is followed by a colon, the option is expected to have an | |
ccc6cda3 | 2766 | argument, which should be separated from it by white space. |
bb70624e JA |
2767 | The colon (@samp{:}) and question mark (@samp{?}) may not be |
2768 | used as option characters. | |
ccc6cda3 JA |
2769 | Each time it is invoked, @code{getopts} |
2770 | places the next option in the shell variable @var{name}, initializing | |
2771 | @var{name} if it does not exist, | |
2772 | and the index of the next argument to be processed into the | |
28ef6c31 JA |
2773 | variable @env{OPTIND}. |
2774 | @env{OPTIND} is initialized to 1 each time the shell or a shell script | |
cce855bc JA |
2775 | is invoked. |
2776 | When an option requires an argument, | |
28ef6c31 JA |
2777 | @code{getopts} places that argument into the variable @env{OPTARG}. |
2778 | The shell does not reset @env{OPTIND} automatically; it must be manually | |
cce855bc JA |
2779 | reset between multiple calls to @code{getopts} within the same shell |
2780 | invocation if a new set of parameters is to be used. | |
2781 | ||
2782 | When the end of options is encountered, @code{getopts} exits with a | |
2783 | return value greater than zero. | |
28ef6c31 | 2784 | @env{OPTIND} is set to the index of the first non-option argument, |
cce855bc JA |
2785 | and @code{name} is set to @samp{?}. |
2786 | ||
2787 | @code{getopts} | |
2788 | normally parses the positional parameters, but if more arguments are | |
2789 | given in @var{args}, @code{getopts} parses those instead. | |
ccc6cda3 JA |
2790 | |
2791 | @code{getopts} can report errors in two ways. If the first character of | |
2792 | @var{optstring} is a colon, @var{silent} | |
2793 | error reporting is used. In normal operation diagnostic messages | |
cce855bc | 2794 | are printed when invalid options or missing option arguments are |
ccc6cda3 | 2795 | encountered. |
28ef6c31 | 2796 | If the variable @env{OPTERR} |
cce855bc | 2797 | is set to 0, no error messages will be displayed, even if the first |
ccc6cda3 JA |
2798 | character of @code{optstring} is not a colon. |
2799 | ||
cce855bc | 2800 | If an invalid option is seen, |
ccc6cda3 | 2801 | @code{getopts} places @samp{?} into @var{name} and, if not silent, |
28ef6c31 | 2802 | prints an error message and unsets @env{OPTARG}. |
ccc6cda3 | 2803 | If @code{getopts} is silent, the option character found is placed in |
28ef6c31 | 2804 | @env{OPTARG} and no diagnostic message is printed. |
ccc6cda3 JA |
2805 | |
2806 | If a required argument is not found, and @code{getopts} | |
2807 | is not silent, a question mark (@samp{?}) is placed in @var{name}, | |
2808 | @code{OPTARG} is unset, and a diagnostic message is printed. | |
2809 | If @code{getopts} is silent, then a colon (@samp{:}) is placed in | |
28ef6c31 | 2810 | @var{name} and @env{OPTARG} is set to the option character found. |
ccc6cda3 | 2811 | |
ccc6cda3 JA |
2812 | @item hash |
2813 | @btindex hash | |
2814 | @example | |
0628567a | 2815 | hash [-r] [-p @var{filename}] [-dt] [@var{name}] |
ccc6cda3 | 2816 | @end example |
cce855bc JA |
2817 | Remember the full pathnames of commands specified as @var{name} arguments, |
2818 | so they need not be searched for on subsequent invocations. | |
2819 | The commands are found by searching through the directories listed in | |
28ef6c31 JA |
2820 | @env{$PATH}. |
2821 | The @option{-p} option inhibits the path search, and @var{filename} is | |
cce855bc | 2822 | used as the location of @var{name}. |
28ef6c31 | 2823 | The @option{-r} option causes the shell to forget all remembered locations. |
7117c2d2 JA |
2824 | The @option{-d} option causes the shell to forget the remembered location |
2825 | of each @var{name}. | |
f73dda09 JA |
2826 | If the @option{-t} option is supplied, the full pathname to which each |
2827 | @var{name} corresponds is printed. If multiple @var{name} arguments are | |
2828 | supplied with @option{-t} the @var{name} is printed before the hashed | |
2829 | full pathname. | |
7117c2d2 JA |
2830 | The @option{-l} option causes output to be displayed in a format |
2831 | that may be reused as input. | |
2832 | If no arguments are given, or if only @option{-l} is supplied, | |
2833 | information about remembered commands is printed. | |
cce855bc JA |
2834 | The return status is zero unless a @var{name} is not found or an invalid |
2835 | option is supplied. | |
ccc6cda3 JA |
2836 | |
2837 | @item pwd | |
2838 | @btindex pwd | |
2839 | @example | |
2840 | pwd [-LP] | |
2841 | @end example | |
bb70624e | 2842 | Print the absolute pathname of the current working directory. |
28ef6c31 | 2843 | If the @option{-P} option is supplied, the pathname printed will not |
cce855bc | 2844 | contain symbolic links. |
28ef6c31 | 2845 | If the @option{-L} option is supplied, the pathname printed may contain |
cce855bc JA |
2846 | symbolic links. |
2847 | The return status is zero unless an error is encountered while | |
2848 | determining the name of the current directory or an invalid option | |
2849 | is supplied. | |
ccc6cda3 JA |
2850 | |
2851 | @item readonly | |
2852 | @btindex readonly | |
2853 | @example | |
b80f6443 | 2854 | readonly [-apf] [@var{name}[=@var{value}]] @dots{} |
ccc6cda3 | 2855 | @end example |
cce855bc JA |
2856 | Mark each @var{name} as readonly. |
2857 | The values of these names may not be changed by subsequent assignment. | |
28ef6c31 | 2858 | If the @option{-f} option is supplied, each @var{name} refers to a shell |
cce855bc | 2859 | function. |
28ef6c31 JA |
2860 | The @option{-a} option means each @var{name} refers to an array variable. |
2861 | If no @var{name} arguments are given, or if the @option{-p} | |
ccc6cda3 | 2862 | option is supplied, a list of all readonly names is printed. |
28ef6c31 | 2863 | The @option{-p} option causes output to be displayed in a format that |
cce855bc | 2864 | may be reused as input. |
b80f6443 JA |
2865 | If a variable name is followed by =@var{value}, the value of |
2866 | the variable is set to @var{value}. | |
cce855bc JA |
2867 | The return status is zero unless an invalid option is supplied, one of |
2868 | the @var{name} arguments is not a valid shell variable or function name, | |
28ef6c31 | 2869 | or the @option{-f} option is supplied with a name that is not a shell function. |
ccc6cda3 JA |
2870 | |
2871 | @item return | |
2872 | @btindex return | |
2873 | @example | |
2874 | return [@var{n}] | |
2875 | @end example | |
cce855bc | 2876 | Cause a shell function to exit with the return value @var{n}. |
bb70624e JA |
2877 | If @var{n} is not supplied, the return value is the exit status of the |
2878 | last command executed in the function. | |
cce855bc | 2879 | This may also be used to terminate execution of a script being executed |
bb70624e JA |
2880 | with the @code{.} (or @code{source}) builtin, returning either @var{n} or |
2881 | the exit status of the last command executed within the script as the exit | |
2882 | status of the script. | |
b80f6443 JA |
2883 | Any command associated with the @code{RETURN} trap is executed |
2884 | before execution resumes after the function or script. | |
f73dda09 | 2885 | The return status is non-zero if @code{return} is used outside a function |
bb70624e | 2886 | and not during the execution of a script by @code{.} or @code{source}. |
ccc6cda3 JA |
2887 | |
2888 | @item shift | |
2889 | @btindex shift | |
2890 | @example | |
2891 | shift [@var{n}] | |
2892 | @end example | |
cce855bc JA |
2893 | Shift the positional parameters to the left by @var{n}. |
2894 | The positional parameters from @var{n}+1 @dots{} @code{$#} are | |
2895 | renamed to @code{$1} @dots{} @code{$#}-@var{n}+1. | |
2896 | Parameters represented by the numbers @code{$#} to @var{n}+1 are unset. | |
2897 | @var{n} must be a non-negative number less than or equal to @code{$#}. | |
2898 | If @var{n} is zero or greater than @code{$#}, the positional parameters | |
2899 | are not changed. | |
bb70624e | 2900 | If @var{n} is not supplied, it is assumed to be 1. |
cce855bc JA |
2901 | The return status is zero unless @var{n} is greater than @code{$#} or |
2902 | less than zero, non-zero otherwise. | |
ccc6cda3 JA |
2903 | |
2904 | @item test | |
2905 | @itemx [ | |
2906 | @btindex test | |
2907 | @btindex [ | |
cce855bc JA |
2908 | Evaluate a conditional expression @var{expr}. |
2909 | Each operator and operand must be a separate argument. | |
2910 | Expressions are composed of the primaries described below in | |
2911 | @ref{Bash Conditional Expressions}. | |
95732b49 JA |
2912 | @code{test} does not accept any options, nor does it accept and ignore |
2913 | an argument of @option{--} as signifying the end of options. | |
cce855bc | 2914 | |
bb70624e JA |
2915 | When the @code{[} form is used, the last argument to the command must |
2916 | be a @code{]}. | |
2917 | ||
cce855bc JA |
2918 | Expressions may be combined using the following operators, listed in |
2919 | decreasing order of precedence. | |
2920 | ||
2921 | @table @code | |
2922 | @item ! @var{expr} | |
2923 | True if @var{expr} is false. | |
2924 | ||
2925 | @item ( @var{expr} ) | |
2926 | Returns the value of @var{expr}. | |
2927 | This may be used to override the normal precedence of operators. | |
2928 | ||
2929 | @item @var{expr1} -a @var{expr2} | |
2930 | True if both @var{expr1} and @var{expr2} are true. | |
2931 | ||
2932 | @item @var{expr1} -o @var{expr2} | |
2933 | True if either @var{expr1} or @var{expr2} is true. | |
2934 | @end table | |
2935 | ||
2936 | The @code{test} and @code{[} builtins evaluate conditional | |
2937 | expressions using a set of rules based on the number of arguments. | |
2938 | ||
2939 | @table @asis | |
2940 | @item 0 arguments | |
2941 | The expression is false. | |
2942 | ||
2943 | @item 1 argument | |
2944 | The expression is true if and only if the argument is not null. | |
2945 | ||
2946 | @item 2 arguments | |
2947 | If the first argument is @samp{!}, the expression is true if and | |
2948 | only if the second argument is null. | |
2949 | If the first argument is one of the unary conditional operators | |
2950 | (@pxref{Bash Conditional Expressions}), the expression | |
2951 | is true if the unary test is true. | |
2952 | If the first argument is not a valid unary operator, the expression is | |
2953 | false. | |
2954 | ||
2955 | @item 3 arguments | |
2956 | If the second argument is one of the binary conditional | |
2957 | operators (@pxref{Bash Conditional Expressions}), the | |
2958 | result of the expression is the result of the binary test using the | |
2959 | first and third arguments as operands. | |
2960 | If the first argument is @samp{!}, the value is the negation of | |
2961 | the two-argument test using the second and third arguments. | |
2962 | If the first argument is exactly @samp{(} and the third argument is | |
2963 | exactly @samp{)}, the result is the one-argument test of the second | |
2964 | argument. | |
2965 | Otherwise, the expression is false. | |
2966 | The @samp{-a} and @samp{-o} operators are considered binary operators | |
2967 | in this case. | |
2968 | ||
2969 | @item 4 arguments | |
2970 | If the first argument is @samp{!}, the result is the negation of | |
2971 | the three-argument expression composed of the remaining arguments. | |
2972 | Otherwise, the expression is parsed and evaluated according to | |
2973 | precedence using the rules listed above. | |
2974 | ||
2975 | @item 5 or more arguments | |
2976 | The expression is parsed and evaluated according to precedence | |
2977 | using the rules listed above. | |
2978 | @end table | |
ccc6cda3 JA |
2979 | |
2980 | @item times | |
2981 | @btindex times | |
2982 | @example | |
2983 | times | |
2984 | @end example | |
2985 | Print out the user and system times used by the shell and its children. | |
cce855bc | 2986 | The return status is zero. |
ccc6cda3 JA |
2987 | |
2988 | @item trap | |
2989 | @btindex trap | |
2990 | @example | |
d166f048 | 2991 | trap [-lp] [@var{arg}] [@var{sigspec} @dots{}] |
ccc6cda3 JA |
2992 | @end example |
2993 | The commands in @var{arg} are to be read and executed when the | |
b80f6443 JA |
2994 | shell receives signal @var{sigspec}. If @var{arg} is absent (and |
2995 | there is a single @var{sigspec}) or | |
2996 | equal to @samp{-}, each specified signal's disposition is reset | |
2997 | to the value it had when the shell was started. | |
d166f048 JA |
2998 | If @var{arg} is the null string, then the signal specified by |
2999 | each @var{sigspec} is ignored by the shell and commands it invokes. | |
28ef6c31 | 3000 | If @var{arg} is not present and @option{-p} has been supplied, |
bb70624e JA |
3001 | the shell displays the trap commands associated with each @var{sigspec}. |
3002 | If no arguments are supplied, or | |
28ef6c31 | 3003 | only @option{-p} is given, @code{trap} prints the list of commands |
cce855bc JA |
3004 | associated with each signal number in a form that may be reused as |
3005 | shell input. | |
b80f6443 JA |
3006 | The @option{-l} option causes the shell to print a list of signal names |
3007 | and their corresponding numbers. | |
3008 | Each @var{sigspec} is either a signal name or a signal number. | |
3009 | Signal names are case insensitive and the @code{SIG} prefix is optional. | |
d166f048 JA |
3010 | If a @var{sigspec} |
3011 | is @code{0} or @code{EXIT}, @var{arg} is executed when the shell exits. | |
3012 | If a @var{sigspec} is @code{DEBUG}, the command @var{arg} is executed | |
b80f6443 JA |
3013 | before every simple command, @code{for} command, @code{case} command, |
3014 | @code{select} command, every arithmetic @code{for} command, and before | |
3015 | the first command executes in a shell function. | |
3016 | Refer to the description of the @code{extglob} option to the | |
3017 | @code{shopt} builtin (@pxref{Bash Builtins}) for details of its | |
3018 | effect on the @code{DEBUG} trap. | |
f73dda09 | 3019 | If a @var{sigspec} is @code{ERR}, the command @var{arg} |
b80f6443 JA |
3020 | is executed whenever a simple command has a non-zero exit status, |
3021 | subject to the following conditions. | |
3022 | The @code{ERR} trap is not executed if the failed command is part of the | |
3023 | command list immediately following an @code{until} or @code{while} keyword, | |
3024 | part of the test in an @code{if} statement, | |
f73dda09 JA |
3025 | part of a @code{&&} or @code{||} list, or if the command's return |
3026 | status is being inverted using @code{!}. | |
b80f6443 JA |
3027 | These are the same conditions obeyed by the @code{errexit} option. |
3028 | If a @var{sigspec} is @code{RETURN}, the command @var{arg} is executed | |
3029 | each time a shell function or a script executed with the @code{.} or | |
3030 | @code{source} builtins finishes executing. | |
ccc6cda3 JA |
3031 | |
3032 | Signals ignored upon entry to the shell cannot be trapped or reset. | |
0628567a JA |
3033 | Trapped signals that are not being ignored are reset to their original |
3034 | values in a child process when it is created. | |
ccc6cda3 | 3035 | |
cce855bc JA |
3036 | The return status is zero unless a @var{sigspec} does not specify a |
3037 | valid signal. | |
3038 | ||
ccc6cda3 JA |
3039 | @item umask |
3040 | @btindex umask | |
3041 | @example | |
cce855bc | 3042 | umask [-p] [-S] [@var{mode}] |
ccc6cda3 JA |
3043 | @end example |
3044 | Set the shell process's file creation mask to @var{mode}. If | |
3045 | @var{mode} begins with a digit, it is interpreted as an octal number; | |
3046 | if not, it is interpreted as a symbolic mode mask similar | |
3047 | to that accepted by the @code{chmod} command. If @var{mode} is | |
28ef6c31 | 3048 | omitted, the current value of the mask is printed. If the @option{-S} |
ccc6cda3 JA |
3049 | option is supplied without a @var{mode} argument, the mask is printed |
3050 | in a symbolic format. | |
28ef6c31 | 3051 | If the @option{-p} option is supplied, and @var{mode} |
cce855bc JA |
3052 | is omitted, the output is in a form that may be reused as input. |
3053 | The return status is zero if the mode is successfully changed or if | |
3054 | no @var{mode} argument is supplied, and non-zero otherwise. | |
ccc6cda3 | 3055 | |
bb70624e JA |
3056 | Note that when the mode is interpreted as an octal number, each number |
3057 | of the umask is subtracted from @code{7}. Thus, a umask of @code{022} | |
3058 | results in permissions of @code{755}. | |
3059 | ||
ccc6cda3 JA |
3060 | @item unset |
3061 | @btindex unset | |
3062 | @example | |
3063 | unset [-fv] [@var{name}] | |
3064 | @end example | |
3065 | Each variable or function @var{name} is removed. | |
28ef6c31 | 3066 | If no options are supplied, or the @option{-v} option is given, each |
ccc6cda3 | 3067 | @var{name} refers to a shell variable. |
28ef6c31 | 3068 | If the @option{-f} option is given, the @var{name}s refer to shell |
ccc6cda3 | 3069 | functions, and the function definition is removed. |
cce855bc | 3070 | Readonly variables and functions may not be unset. |
b80f6443 | 3071 | The return status is zero unless a @var{name} is readonly. |
ccc6cda3 JA |
3072 | @end table |
3073 | ||
bb70624e JA |
3074 | @node Bash Builtins |
3075 | @section Bash Builtin Commands | |
ccc6cda3 | 3076 | |
bb70624e JA |
3077 | This section describes builtin commands which are unique to |
3078 | or have been extended in Bash. | |
0628567a | 3079 | Some of these commands are specified in the @sc{posix} standard. |
ccc6cda3 | 3080 | |
bb70624e | 3081 | @table @code |
ccc6cda3 | 3082 | |
bb70624e JA |
3083 | @item alias |
3084 | @btindex alias | |
3085 | @example | |
3086 | alias [@code{-p}] [@var{name}[=@var{value}] @dots{}] | |
3087 | @end example | |
ccc6cda3 | 3088 | |
28ef6c31 | 3089 | Without arguments or with the @option{-p} option, @code{alias} prints |
bb70624e JA |
3090 | the list of aliases on the standard output in a form that allows |
3091 | them to be reused as input. | |
3092 | If arguments are supplied, an alias is defined for each @var{name} | |
3093 | whose @var{value} is given. If no @var{value} is given, the name | |
3094 | and value of the alias is printed. | |
3095 | Aliases are described in @ref{Aliases}. | |
ccc6cda3 | 3096 | |
bb70624e JA |
3097 | @item bind |
3098 | @btindex bind | |
3099 | @example | |
3100 | bind [-m @var{keymap}] [-lpsvPSV] | |
3101 | bind [-m @var{keymap}] [-q @var{function}] [-u @var{function}] [-r @var{keyseq}] | |
3102 | bind [-m @var{keymap}] -f @var{filename} | |
3103 | bind [-m @var{keymap}] -x @var{keyseq:shell-command} | |
3104 | bind [-m @var{keymap}] @var{keyseq:function-name} | |
7117c2d2 | 3105 | bind @var{readline-command} |
bb70624e | 3106 | @end example |
ccc6cda3 | 3107 | |
bb70624e | 3108 | Display current Readline (@pxref{Command Line Editing}) |
7117c2d2 JA |
3109 | key and function bindings, |
3110 | bind a key sequence to a Readline function or macro, | |
3111 | or set a Readline variable. | |
3112 | Each non-option argument is a command as it would appear in a | |
bb70624e | 3113 | a Readline initialization file (@pxref{Readline Init File}), |
7117c2d2 | 3114 | but each binding or command must be passed as a separate argument; e.g., |
bb70624e JA |
3115 | @samp{"\C-x\C-r":re-read-init-file}. |
3116 | Options, if supplied, have the following meanings: | |
cce855bc | 3117 | |
bb70624e JA |
3118 | @table @code |
3119 | @item -m @var{keymap} | |
3120 | Use @var{keymap} as the keymap to be affected by | |
3121 | the subsequent bindings. Acceptable @var{keymap} | |
3122 | names are | |
3123 | @code{emacs}, | |
3124 | @code{emacs-standard}, | |
3125 | @code{emacs-meta}, | |
3126 | @code{emacs-ctlx}, | |
3127 | @code{vi}, | |
28ef6c31 | 3128 | @code{vi-move}, |
bb70624e JA |
3129 | @code{vi-command}, and |
3130 | @code{vi-insert}. | |
3131 | @code{vi} is equivalent to @code{vi-command}; | |
3132 | @code{emacs} is equivalent to @code{emacs-standard}. | |
cce855bc | 3133 | |
bb70624e JA |
3134 | @item -l |
3135 | List the names of all Readline functions. | |
cce855bc | 3136 | |
bb70624e JA |
3137 | @item -p |
3138 | Display Readline function names and bindings in such a way that they | |
3139 | can be used as input or in a Readline initialization file. | |
cce855bc | 3140 | |
bb70624e JA |
3141 | @item -P |
3142 | List current Readline function names and bindings. | |
ccc6cda3 | 3143 | |
bb70624e JA |
3144 | @item -v |
3145 | Display Readline variable names and values in such a way that they | |
3146 | can be used as input or in a Readline initialization file. | |
ccc6cda3 | 3147 | |
bb70624e JA |
3148 | @item -V |
3149 | List current Readline variable names and values. | |
ccc6cda3 | 3150 | |
bb70624e JA |
3151 | @item -s |
3152 | Display Readline key sequences bound to macros and the strings they output | |
3153 | in such a way that they can be used as input or in a Readline | |
3154 | initialization file. | |
ccc6cda3 | 3155 | |
bb70624e JA |
3156 | @item -S |
3157 | Display Readline key sequences bound to macros and the strings they output. | |
ccc6cda3 | 3158 | |
bb70624e JA |
3159 | @item -f @var{filename} |
3160 | Read key bindings from @var{filename}. | |
ccc6cda3 | 3161 | |
bb70624e JA |
3162 | @item -q @var{function} |
3163 | Query about which keys invoke the named @var{function}. | |
ccc6cda3 | 3164 | |
bb70624e JA |
3165 | @item -u @var{function} |
3166 | Unbind all keys bound to the named @var{function}. | |
cce855bc | 3167 | |
bb70624e JA |
3168 | @item -r @var{keyseq} |
3169 | Remove any current binding for @var{keyseq}. | |
ccc6cda3 | 3170 | |
bb70624e JA |
3171 | @item -x @var{keyseq:shell-command} |
3172 | Cause @var{shell-command} to be executed whenever @var{keyseq} is | |
3173 | entered. | |
ccc6cda3 | 3174 | |
bb70624e | 3175 | @end table |
ccc6cda3 | 3176 | |
bb70624e JA |
3177 | @noindent |
3178 | The return status is zero unless an invalid option is supplied or an | |
3179 | error occurs. | |
ccc6cda3 | 3180 | |
bb70624e JA |
3181 | @item builtin |
3182 | @btindex builtin | |
3183 | @example | |
3184 | builtin [@var{shell-builtin} [@var{args}]] | |
3185 | @end example | |
3186 | Run a shell builtin, passing it @var{args}, and return its exit status. | |
3187 | This is useful when defining a shell function with the same | |
3188 | name as a shell builtin, retaining the functionality of the builtin within | |
3189 | the function. | |
3190 | The return status is non-zero if @var{shell-builtin} is not a shell | |
3191 | builtin command. | |
ccc6cda3 | 3192 | |
b80f6443 JA |
3193 | @item caller |
3194 | @btindex caller | |
3195 | @example | |
3196 | caller [@var{expr}] | |
3197 | @end example | |
3198 | Returns the context of any active subroutine call (a shell function or | |
3199 | a script executed with the @code{.} or @code{source} builtins). | |
3200 | ||
3201 | Without @var{expr}, @code{caller} displays the line number and source | |
3202 | filename of the current subroutine call. | |
3203 | If a non-negative integer is supplied as @var{expr}, @code{caller} | |
3204 | displays the line number, subroutine name, and source file corresponding | |
3205 | to that position in the current execution call stack. This extra | |
3206 | information may be used, for example, to print a stack trace. The | |
3207 | current frame is frame 0. | |
3208 | ||
3209 | The return value is 0 unless the shell is not executing a subroutine | |
3210 | call or @var{expr} does not correspond to a valid position in the | |
3211 | call stack. | |
3212 | ||
bb70624e JA |
3213 | @item command |
3214 | @btindex command | |
3215 | @example | |
3216 | command [-pVv] @var{command} [@var{arguments} @dots{}] | |
3217 | @end example | |
3218 | Runs @var{command} with @var{arguments} ignoring any shell function | |
3219 | named @var{command}. | |
3220 | Only shell builtin commands or commands found by searching the | |
28ef6c31 | 3221 | @env{PATH} are executed. |
bb70624e JA |
3222 | If there is a shell function named @code{ls}, running @samp{command ls} |
3223 | within the function will execute the external command @code{ls} | |
3224 | instead of calling the function recursively. | |
28ef6c31 | 3225 | The @option{-p} option means to use a default value for @env{PATH} |
bb70624e JA |
3226 | that is guaranteed to find all of the standard utilities. |
3227 | The return status in this case is 127 if @var{command} cannot be | |
3228 | found or an error occurred, and the exit status of @var{command} | |
3229 | otherwise. | |
cce855bc | 3230 | |
28ef6c31 JA |
3231 | If either the @option{-V} or @option{-v} option is supplied, a |
3232 | description of @var{command} is printed. The @option{-v} option | |
bb70624e | 3233 | causes a single word indicating the command or file name used to |
28ef6c31 | 3234 | invoke @var{command} to be displayed; the @option{-V} option produces |
bb70624e JA |
3235 | a more verbose description. In this case, the return status is |
3236 | zero if @var{command} is found, and non-zero if not. | |
cce855bc | 3237 | |
bb70624e JA |
3238 | @item declare |
3239 | @btindex declare | |
3240 | @example | |
b80f6443 | 3241 | declare [-afFirtx] [-p] [@var{name}[=@var{value}] @dots{}] |
bb70624e | 3242 | @end example |
ccc6cda3 | 3243 | |
bb70624e JA |
3244 | Declare variables and give them attributes. If no @var{name}s |
3245 | are given, then display the values of variables instead. | |
ccc6cda3 | 3246 | |
28ef6c31 | 3247 | The @option{-p} option will display the attributes and values of each |
b80f6443 JA |
3248 | @var{name}. |
3249 | When @option{-p} is used, additional options are ignored. | |
28ef6c31 | 3250 | The @option{-F} option inhibits the display of function definitions; |
b80f6443 JA |
3251 | only the function name and attributes are printed. |
3252 | If the @code{extdebug} shell option is enabled using @code{shopt} | |
3253 | (@pxref{Bash Builtins}), the source file name and line number where | |
3254 | the function is defined are displayed as well. | |
3255 | @option{-F} implies @option{-f}. | |
3256 | The following options can be used to restrict output to variables with | |
3257 | the specified attributes or to give variables attributes: | |
cce855bc | 3258 | |
bb70624e JA |
3259 | @table @code |
3260 | @item -a | |
3261 | Each @var{name} is an array variable (@pxref{Arrays}). | |
cce855bc | 3262 | |
bb70624e JA |
3263 | @item -f |
3264 | Use function names only. | |
ccc6cda3 | 3265 | |
bb70624e JA |
3266 | @item -i |
3267 | The variable is to be treated as | |
3268 | an integer; arithmetic evaluation (@pxref{Shell Arithmetic}) is | |
3269 | performed when the variable is assigned a value. | |
ccc6cda3 | 3270 | |
bb70624e JA |
3271 | @item -r |
3272 | Make @var{name}s readonly. These names cannot then be assigned values | |
3273 | by subsequent assignment statements or unset. | |
ccc6cda3 | 3274 | |
7117c2d2 JA |
3275 | @item -t |
3276 | Give each @var{name} the @code{trace} attribute. | |
95732b49 JA |
3277 | Traced functions inherit the @code{DEBUG} and @code{RETURN} traps from |
3278 | the calling shell. | |
7117c2d2 JA |
3279 | The trace attribute has no special meaning for variables. |
3280 | ||
bb70624e JA |
3281 | @item -x |
3282 | Mark each @var{name} for export to subsequent commands via | |
3283 | the environment. | |
3284 | @end table | |
ccc6cda3 | 3285 | |
bb70624e JA |
3286 | Using @samp{+} instead of @samp{-} turns off the attribute instead. |
3287 | When used in a function, @code{declare} makes each @var{name} local, | |
b80f6443 JA |
3288 | as with the @code{local} command. If a variable name is followed by |
3289 | =@var{value}, the value of the variable is set to @var{value}. | |
ccc6cda3 | 3290 | |
bb70624e JA |
3291 | The return status is zero unless an invalid option is encountered, |
3292 | an attempt is made to define a function using @samp{-f foo=bar}, | |
3293 | an attempt is made to assign a value to a readonly variable, | |
3294 | an attempt is made to assign a value to an array variable without | |
3295 | using the compound assignment syntax (@pxref{Arrays}), | |
3296 | one of the @var{names} is not a valid shell variable name, | |
3297 | an attempt is made to turn off readonly status for a readonly variable, | |
3298 | an attempt is made to turn off array status for an array variable, | |
28ef6c31 | 3299 | or an attempt is made to display a non-existent function with @option{-f}. |
ccc6cda3 | 3300 | |
bb70624e JA |
3301 | @item echo |
3302 | @btindex echo | |
3303 | @example | |
3304 | echo [-neE] [@var{arg} @dots{}] | |
3305 | @end example | |
3306 | Output the @var{arg}s, separated by spaces, terminated with a | |
3307 | newline. | |
3308 | The return status is always 0. | |
28ef6c31 JA |
3309 | If @option{-n} is specified, the trailing newline is suppressed. |
3310 | If the @option{-e} option is given, interpretation of the following | |
bb70624e | 3311 | backslash-escaped characters is enabled. |
28ef6c31 | 3312 | The @option{-E} option disables the interpretation of these escape characters, |
bb70624e JA |
3313 | even on systems where they are interpreted by default. |
3314 | The @code{xpg_echo} shell option may be used to | |
3315 | dynamically determine whether or not @code{echo} expands these | |
3316 | escape characters by default. | |
95732b49 JA |
3317 | @code{echo} does not interpret @option{--} to mean the end of options. |
3318 | ||
bb70624e JA |
3319 | @code{echo} interprets the following escape sequences: |
3320 | @table @code | |
3321 | @item \a | |
3322 | alert (bell) | |
3323 | @item \b | |
3324 | backspace | |
3325 | @item \c | |
3326 | suppress trailing newline | |
3327 | @item \e | |
3328 | escape | |
3329 | @item \f | |
3330 | form feed | |
3331 | @item \n | |
3332 | new line | |
3333 | @item \r | |
3334 | carriage return | |
3335 | @item \t | |
3336 | horizontal tab | |
3337 | @item \v | |
3338 | vertical tab | |
3339 | @item \\ | |
3340 | backslash | |
7117c2d2 JA |
3341 | @item \0@var{nnn} |
3342 | the eight-bit character whose value is the octal value @var{nnn} | |
3343 | (zero to three octal digits) | |
f73dda09 JA |
3344 | @item \x@var{HH} |
3345 | the eight-bit character whose value is the hexadecimal value @var{HH} | |
3346 | (one or two hex digits) | |
bb70624e | 3347 | @end table |
ccc6cda3 | 3348 | |
bb70624e JA |
3349 | @item enable |
3350 | @btindex enable | |
3351 | @example | |
3352 | enable [-n] [-p] [-f @var{filename}] [-ads] [@var{name} @dots{}] | |
3353 | @end example | |
3354 | Enable and disable builtin shell commands. | |
3355 | Disabling a builtin allows a disk command which has the same name | |
3356 | as a shell builtin to be executed without specifying a full pathname, | |
3357 | even though the shell normally searches for builtins before disk commands. | |
28ef6c31 | 3358 | If @option{-n} is used, the @var{name}s become disabled. Otherwise |
bb70624e | 3359 | @var{name}s are enabled. For example, to use the @code{test} binary |
28ef6c31 | 3360 | found via @env{$PATH} instead of the shell builtin version, type |
bb70624e | 3361 | @samp{enable -n test}. |
ccc6cda3 | 3362 | |
28ef6c31 | 3363 | If the @option{-p} option is supplied, or no @var{name} arguments appear, |
bb70624e JA |
3364 | a list of shell builtins is printed. With no other arguments, the list |
3365 | consists of all enabled shell builtins. | |
28ef6c31 | 3366 | The @option{-a} option means to list |
bb70624e | 3367 | each builtin with an indication of whether or not it is enabled. |
ccc6cda3 | 3368 | |
28ef6c31 | 3369 | The @option{-f} option means to load the new builtin command @var{name} |
bb70624e | 3370 | from shared object @var{filename}, on systems that support dynamic loading. |
28ef6c31 | 3371 | The @option{-d} option will delete a builtin loaded with @option{-f}. |
ccc6cda3 | 3372 | |
bb70624e | 3373 | If there are no options, a list of the shell builtins is displayed. |
28ef6c31 JA |
3374 | The @option{-s} option restricts @code{enable} to the @sc{posix} special |
3375 | builtins. If @option{-s} is used with @option{-f}, the new builtin becomes | |
bb70624e | 3376 | a special builtin (@pxref{Special Builtins}). |
ccc6cda3 | 3377 | |
bb70624e JA |
3378 | The return status is zero unless a @var{name} is not a shell builtin |
3379 | or there is an error loading a new builtin from a shared object. | |
cce855bc | 3380 | |
bb70624e JA |
3381 | @item help |
3382 | @btindex help | |
3383 | @example | |
3384 | help [-s] [@var{pattern}] | |
3385 | @end example | |
3386 | Display helpful information about builtin commands. | |
3387 | If @var{pattern} is specified, @code{help} gives detailed help | |
3388 | on all commands matching @var{pattern}, otherwise a list of | |
3389 | the builtins is printed. | |
28ef6c31 | 3390 | The @option{-s} option restricts the information displayed to a short |
bb70624e JA |
3391 | usage synopsis. |
3392 | The return status is zero unless no command matches @var{pattern}. | |
ccc6cda3 | 3393 | |
bb70624e JA |
3394 | @item let |
3395 | @btindex let | |
3396 | @example | |
3397 | let @var{expression} [@var{expression}] | |
3398 | @end example | |
3399 | The @code{let} builtin allows arithmetic to be performed on shell | |
3400 | variables. Each @var{expression} is evaluated according to the | |
3401 | rules given below in @ref{Shell Arithmetic}. If the | |
3402 | last @var{expression} evaluates to 0, @code{let} returns 1; | |
3403 | otherwise 0 is returned. | |
ccc6cda3 | 3404 | |
bb70624e JA |
3405 | @item local |
3406 | @btindex local | |
3407 | @example | |
b80f6443 | 3408 | local [@var{option}] @var{name}[=@var{value}] @dots{} |
bb70624e JA |
3409 | @end example |
3410 | For each argument, a local variable named @var{name} is created, | |
3411 | and assigned @var{value}. | |
3412 | The @var{option} can be any of the options accepted by @code{declare}. | |
3413 | @code{local} can only be used within a function; it makes the variable | |
3414 | @var{name} have a visible scope restricted to that function and its | |
3415 | children. The return status is zero unless @code{local} is used outside | |
3416 | a function, an invalid @var{name} is supplied, or @var{name} is a | |
3417 | readonly variable. | |
ccc6cda3 | 3418 | |
bb70624e JA |
3419 | @item logout |
3420 | @btindex logout | |
3421 | @example | |
3422 | logout [@var{n}] | |
3423 | @end example | |
3424 | Exit a login shell, returning a status of @var{n} to the shell's | |
3425 | parent. | |
cce855bc | 3426 | |
bb70624e JA |
3427 | @item printf |
3428 | @btindex printf | |
3429 | @example | |
95732b49 | 3430 | @code{printf} [-v @var{var}] @var{format} [@var{arguments}] |
bb70624e JA |
3431 | @end example |
3432 | Write the formatted @var{arguments} to the standard output under the | |
3433 | control of the @var{format}. | |
3434 | The @var{format} is a character string which contains three types of objects: | |
3435 | plain characters, which are simply copied to standard output, character | |
3436 | escape sequences, which are converted and copied to the standard output, and | |
3437 | format specifications, each of which causes printing of the next successive | |
3438 | @var{argument}. | |
3439 | In addition to the standard @code{printf(1)} formats, @samp{%b} causes | |
3440 | @code{printf} to expand backslash escape sequences in the corresponding | |
b80f6443 JA |
3441 | @var{argument}, |
3442 | (except that @samp{\c} terminates output, backslashes in | |
3443 | @samp{\'}, @samp{\"}, and @samp{\?} are not removed, and octal escapes | |
3444 | beginning with @samp{\0} may contain up to four digits), | |
3445 | and @samp{%q} causes @code{printf} to output the | |
bb70624e | 3446 | corresponding @var{argument} in a format that can be reused as shell input. |
cce855bc | 3447 | |
95732b49 JA |
3448 | The @option{-v} option causes the output to be assigned to the variable |
3449 | @var{var} rather than being printed to the standard output. | |
3450 | ||
bb70624e JA |
3451 | The @var{format} is reused as necessary to consume all of the @var{arguments}. |
3452 | If the @var{format} requires more @var{arguments} than are supplied, the | |
3453 | extra format specifications behave as if a zero value or null string, as | |
3454 | appropriate, had been supplied. The return value is zero on success, | |
3455 | non-zero on failure. | |
ccc6cda3 | 3456 | |
bb70624e JA |
3457 | @item read |
3458 | @btindex read | |
3459 | @example | |
7117c2d2 | 3460 | read [-ers] [-a @var{aname}] [-d @var{delim}] [-n @var{nchars}] [-p @var{prompt}] [-t @var{timeout}] [-u @var{fd}] [@var{name} @dots{}] |
bb70624e | 3461 | @end example |
7117c2d2 JA |
3462 | One line is read from the standard input, or from the file descriptor |
3463 | @var{fd} supplied as an argument to the @option{-u} option, and the first word | |
bb70624e JA |
3464 | is assigned to the first @var{name}, the second word to the second @var{name}, |
3465 | and so on, with leftover words and their intervening separators assigned | |
3466 | to the last @var{name}. | |
7117c2d2 | 3467 | If there are fewer words read from the input stream than names, |
bb70624e | 3468 | the remaining names are assigned empty values. |
28ef6c31 | 3469 | The characters in the value of the @env{IFS} variable |
bb70624e JA |
3470 | are used to split the line into words. |
3471 | The backslash character @samp{\} may be used to remove any special | |
3472 | meaning for the next character read and for line continuation. | |
3473 | If no names are supplied, the line read is assigned to the | |
28ef6c31 | 3474 | variable @env{REPLY}. |
7117c2d2 JA |
3475 | The return code is zero, unless end-of-file is encountered, @code{read} |
3476 | times out, or an invalid file descriptor is supplied as the argument to | |
3477 | @option{-u}. | |
bb70624e | 3478 | Options, if supplied, have the following meanings: |
ccc6cda3 | 3479 | |
bb70624e JA |
3480 | @table @code |
3481 | @item -a @var{aname} | |
3482 | The words are assigned to sequential indices of the array variable | |
3483 | @var{aname}, starting at 0. | |
3484 | All elements are removed from @var{aname} before the assignment. | |
3485 | Other @var{name} arguments are ignored. | |
ccc6cda3 | 3486 | |
bb70624e JA |
3487 | @item -d @var{delim} |
3488 | The first character of @var{delim} is used to terminate the input line, | |
3489 | rather than newline. | |
ccc6cda3 | 3490 | |
bb70624e JA |
3491 | @item -e |
3492 | Readline (@pxref{Command Line Editing}) is used to obtain the line. | |
ccc6cda3 | 3493 | |
bb70624e JA |
3494 | @item -n @var{nchars} |
3495 | @code{read} returns after reading @var{nchars} characters rather than | |
3496 | waiting for a complete line of input. | |
ccc6cda3 | 3497 | |
bb70624e JA |
3498 | @item -p @var{prompt} |
3499 | Display @var{prompt}, without a trailing newline, before attempting | |
3500 | to read any input. | |
3501 | The prompt is displayed only if input is coming from a terminal. | |
ccc6cda3 | 3502 | |
bb70624e JA |
3503 | @item -r |
3504 | If this option is given, backslash does not act as an escape character. | |
3505 | The backslash is considered to be part of the line. | |
3506 | In particular, a backslash-newline pair may not be used as a line | |
3507 | continuation. | |
ccc6cda3 | 3508 | |
bb70624e JA |
3509 | @item -s |
3510 | Silent mode. If input is coming from a terminal, characters are | |
3511 | not echoed. | |
ccc6cda3 | 3512 | |
bb70624e JA |
3513 | @item -t @var{timeout} |
3514 | Cause @code{read} to time out and return failure if a complete line of | |
3515 | input is not read within @var{timeout} seconds. | |
3516 | This option has no effect if @code{read} is not reading input from the | |
3517 | terminal or a pipe. | |
ccc6cda3 | 3518 | |
7117c2d2 JA |
3519 | @item -u @var{fd} |
3520 | Read input from file descriptor @var{fd}. | |
3521 | ||
bb70624e | 3522 | @end table |
ccc6cda3 | 3523 | |
bb70624e JA |
3524 | @item shopt |
3525 | @btindex shopt | |
3526 | @example | |
3527 | shopt [-pqsu] [-o] [@var{optname} @dots{}] | |
3528 | @end example | |
3529 | Toggle the values of variables controlling optional shell behavior. | |
28ef6c31 | 3530 | With no options, or with the @option{-p} option, a list of all settable |
bb70624e | 3531 | options is displayed, with an indication of whether or not each is set. |
28ef6c31 | 3532 | The @option{-p} option causes output to be displayed in a form that |
bb70624e JA |
3533 | may be reused as input. |
3534 | Other options have the following meanings: | |
cce855bc | 3535 | |
bb70624e JA |
3536 | @table @code |
3537 | @item -s | |
3538 | Enable (set) each @var{optname}. | |
cce855bc | 3539 | |
bb70624e JA |
3540 | @item -u |
3541 | Disable (unset) each @var{optname}. | |
ccc6cda3 | 3542 | |
bb70624e JA |
3543 | @item -q |
3544 | Suppresses normal output; the return status | |
3545 | indicates whether the @var{optname} is set or unset. | |
28ef6c31 | 3546 | If multiple @var{optname} arguments are given with @option{-q}, |
bb70624e JA |
3547 | the return status is zero if all @var{optnames} are enabled; |
3548 | non-zero otherwise. | |
ccc6cda3 | 3549 | |
bb70624e JA |
3550 | @item -o |
3551 | Restricts the values of | |
28ef6c31 | 3552 | @var{optname} to be those defined for the @option{-o} option to the |
bb70624e JA |
3553 | @code{set} builtin (@pxref{The Set Builtin}). |
3554 | @end table | |
cce855bc | 3555 | |
28ef6c31 | 3556 | If either @option{-s} or @option{-u} |
bb70624e JA |
3557 | is used with no @var{optname} arguments, the display is limited to |
3558 | those options which are set or unset, respectively. | |
ccc6cda3 | 3559 | |
bb70624e JA |
3560 | Unless otherwise noted, the @code{shopt} options are disabled (off) |
3561 | by default. | |
cce855bc | 3562 | |
bb70624e JA |
3563 | The return status when listing options is zero if all @var{optnames} |
3564 | are enabled, non-zero otherwise. When setting or unsetting options, | |
3565 | the return status is zero unless an @var{optname} is not a valid shell | |
3566 | option. | |
ccc6cda3 | 3567 | |
bb70624e JA |
3568 | The list of @code{shopt} options is: |
3569 | @table @code | |
3570 | @item cdable_vars | |
3571 | If this is set, an argument to the @code{cd} | |
3572 | builtin command that | |
3573 | is not a directory is assumed to be the name of a variable whose | |
3574 | value is the directory to change to. | |
ccc6cda3 | 3575 | |
bb70624e JA |
3576 | @item cdspell |
3577 | If set, minor errors in the spelling of a directory component in a | |
3578 | @code{cd} command will be corrected. | |
3579 | The errors checked for are transposed characters, | |
3580 | a missing character, and a character too many. | |
3581 | If a correction is found, the corrected path is printed, | |
3582 | and the command proceeds. | |
3583 | This option is only used by interactive shells. | |
ccc6cda3 | 3584 | |
bb70624e JA |
3585 | @item checkhash |
3586 | If this is set, Bash checks that a command found in the hash | |
3587 | table exists before trying to execute it. If a hashed command no | |
3588 | longer exists, a normal path search is performed. | |
ccc6cda3 | 3589 | |
bb70624e JA |
3590 | @item checkwinsize |
3591 | If set, Bash checks the window size after each command | |
3592 | and, if necessary, updates the values of | |
28ef6c31 | 3593 | @env{LINES} and @env{COLUMNS}. |
ccc6cda3 | 3594 | |
bb70624e JA |
3595 | @item cmdhist |
3596 | If set, Bash | |
3597 | attempts to save all lines of a multiple-line | |
3598 | command in the same history entry. This allows | |
3599 | easy re-editing of multi-line commands. | |
cce855bc | 3600 | |
bb70624e JA |
3601 | @item dotglob |
3602 | If set, Bash includes filenames beginning with a `.' in | |
3603 | the results of filename expansion. | |
ccc6cda3 | 3604 | |
bb70624e JA |
3605 | @item execfail |
3606 | If this is set, a non-interactive shell will not exit if | |
3607 | it cannot execute the file specified as an argument to the @code{exec} | |
3608 | builtin command. An interactive shell does not exit if @code{exec} | |
3609 | fails. | |
cce855bc | 3610 | |
bb70624e JA |
3611 | @item expand_aliases |
3612 | If set, aliases are expanded as described below under Aliases, | |
3613 | @ref{Aliases}. | |
3614 | This option is enabled by default for interactive shells. | |
ccc6cda3 | 3615 | |
b80f6443 JA |
3616 | @item extdebug |
3617 | If set, behavior intended for use by debuggers is enabled: | |
3618 | ||
3619 | @enumerate | |
3620 | @item | |
3621 | The @option{-F} option to the @code{declare} builtin (@pxref{Bash Builtins}) | |
3622 | displays the source file name and line number corresponding to each function | |
3623 | name supplied as an argument. | |
3624 | ||
3625 | @item | |
3626 | If the command run by the @code{DEBUG} trap returns a non-zero value, the | |
3627 | next command is skipped and not executed. | |
3628 | ||
3629 | @item | |
3630 | If the command run by the @code{DEBUG} trap returns a value of 2, and the | |
3631 | shell is executing in a subroutine (a shell function or a shell script | |
3632 | executed by the @code{.} or @code{source} builtins), a call to | |
3633 | @code{return} is simulated. | |
95732b49 JA |
3634 | |
3635 | @item | |
3636 | @code{BASH_ARGC} and @code{BASH_ARGV} are updated as described in their | |
3637 | descriptions (@pxref{Bash Variables}). | |
3638 | ||
3639 | @item | |
3640 | Function tracing is enabled: command substitution, shell functions, and | |
3641 | subshells invoked with @code{( @var{command} )} inherit the | |
3642 | @code{DEBUG} and @code{RETURN} traps. | |
3643 | ||
3644 | @item | |
3645 | Error tracing is enabled: command substitution, shell functions, and | |
3646 | subshells invoked with @code{( @var{command} )} inherit the | |
3647 | @code{ERROR} trap. | |
b80f6443 JA |
3648 | @end enumerate |
3649 | ||
bb70624e JA |
3650 | @item extglob |
3651 | If set, the extended pattern matching features described above | |
3652 | (@pxref{Pattern Matching}) are enabled. | |
ccc6cda3 | 3653 | |
b80f6443 JA |
3654 | @item extquote |
3655 | If set, @code{$'@var{string}'} and @code{$"@var{string}"} quoting is | |
3656 | performed within @code{$@{@var{parameter}@}} expansions | |
3657 | enclosed in double quotes. This option is enabled by default. | |
3658 | ||
3659 | @item failglob | |
3660 | If set, patterns which fail to match filenames during pathname expansion | |
3661 | result in an expansion error. | |
3662 | ||
3663 | @item force_fignore | |
3664 | If set, the suffixes specified by the @env{FIGNORE} shell variable | |
3665 | cause words to be ignored when performing word completion even if | |
3666 | the ignored words are the only possible completions. | |
3667 | @xref{Bash Variables}, for a description of @env{FIGNORE}. | |
3668 | This option is enabled by default. | |
3669 | ||
3670 | @item gnu_errfmt | |
3671 | If set, shell error messages are written in the standard @sc{gnu} error | |
3672 | message format. | |
3673 | ||
bb70624e JA |
3674 | @item histappend |
3675 | If set, the history list is appended to the file named by the value | |
28ef6c31 | 3676 | of the @env{HISTFILE} |
bb70624e | 3677 | variable when the shell exits, rather than overwriting the file. |
ccc6cda3 | 3678 | |
bb70624e JA |
3679 | @item histreedit |
3680 | If set, and Readline | |
3681 | is being used, a user is given the opportunity to re-edit a | |
3682 | failed history substitution. | |
ccc6cda3 | 3683 | |
bb70624e JA |
3684 | @item histverify |
3685 | If set, and Readline | |
3686 | is being used, the results of history substitution are not immediately | |
3687 | passed to the shell parser. Instead, the resulting line is loaded into | |
3688 | the Readline editing buffer, allowing further modification. | |
ccc6cda3 | 3689 | |
bb70624e JA |
3690 | @item hostcomplete |
3691 | If set, and Readline is being used, Bash will attempt to perform | |
3692 | hostname completion when a word containing a @samp{@@} is being | |
3693 | completed (@pxref{Commands For Completion}). This option is enabled | |
3694 | by default. | |
ccc6cda3 | 3695 | |
bb70624e JA |
3696 | @item huponexit |
3697 | If set, Bash will send @code{SIGHUP} to all jobs when an interactive | |
3698 | login shell exits (@pxref{Signals}). | |
cce855bc | 3699 | |
bb70624e JA |
3700 | @item interactive_comments |
3701 | Allow a word beginning with @samp{#} | |
3702 | to cause that word and all remaining characters on that | |
3703 | line to be ignored in an interactive shell. | |
3704 | This option is enabled by default. | |
ccc6cda3 | 3705 | |
bb70624e JA |
3706 | @item lithist |
3707 | If enabled, and the @code{cmdhist} | |
3708 | option is enabled, multi-line commands are saved to the history with | |
3709 | embedded newlines rather than using semicolon separators where possible. | |
ccc6cda3 | 3710 | |
f73dda09 JA |
3711 | @item login_shell |
3712 | The shell sets this option if it is started as a login shell | |
3713 | (@pxref{Invoking Bash}). | |
3714 | The value may not be changed. | |
3715 | ||
bb70624e JA |
3716 | @item mailwarn |
3717 | If set, and a file that Bash is checking for mail has been | |
3718 | accessed since the last time it was checked, the message | |
3719 | @code{"The mail in @var{mailfile} has been read"} is displayed. | |
ccc6cda3 | 3720 | |
bb70624e JA |
3721 | @item no_empty_cmd_completion |
3722 | If set, and Readline is being used, Bash will not attempt to search | |
28ef6c31 | 3723 | the @env{PATH} for possible completions when completion is attempted |
bb70624e | 3724 | on an empty line. |
ccc6cda3 | 3725 | |
bb70624e JA |
3726 | @item nocaseglob |
3727 | If set, Bash matches filenames in a case-insensitive fashion when | |
3728 | performing filename expansion. | |
ccc6cda3 | 3729 | |
95732b49 JA |
3730 | @item nocasematch |
3731 | If set, Bash matches patterns in a case-insensitive fashion when | |
3732 | performing matching while executing @code{case} or @code{[[} | |
3733 | conditional commands. | |
3734 | ||
bb70624e JA |
3735 | @item nullglob |
3736 | If set, Bash allows filename patterns which match no | |
3737 | files to expand to a null string, rather than themselves. | |
ccc6cda3 | 3738 | |
bb70624e JA |
3739 | @item progcomp |
3740 | If set, the programmable completion facilities | |
3741 | (@pxref{Programmable Completion}) are enabled. | |
3742 | This option is enabled by default. | |
ccc6cda3 | 3743 | |
bb70624e | 3744 | @item promptvars |
b80f6443 JA |
3745 | If set, prompt strings undergo |
3746 | parameter expansion, command substitution, arithmetic | |
3747 | expansion, and quote removal after being expanded | |
3748 | as described below (@pxref{Printing a Prompt}). | |
bb70624e | 3749 | This option is enabled by default. |
ccc6cda3 | 3750 | |
bb70624e JA |
3751 | @item restricted_shell |
3752 | The shell sets this option if it is started in restricted mode | |
3753 | (@pxref{The Restricted Shell}). | |
3754 | The value may not be changed. | |
3755 | This is not reset when the startup files are executed, allowing | |
3756 | the startup files to discover whether or not a shell is restricted. | |
ccc6cda3 | 3757 | |
bb70624e JA |
3758 | @item shift_verbose |
3759 | If this is set, the @code{shift} | |
3760 | builtin prints an error message when the shift count exceeds the | |
3761 | number of positional parameters. | |
ccc6cda3 | 3762 | |
bb70624e | 3763 | @item sourcepath |
28ef6c31 | 3764 | If set, the @code{source} builtin uses the value of @env{PATH} |
bb70624e JA |
3765 | to find the directory containing the file supplied as an argument. |
3766 | This option is enabled by default. | |
ccc6cda3 | 3767 | |
bb70624e JA |
3768 | @item xpg_echo |
3769 | If set, the @code{echo} builtin expands backslash-escape sequences | |
3770 | by default. | |
ccc6cda3 | 3771 | |
bb70624e | 3772 | @end table |
ccc6cda3 | 3773 | |
bb70624e JA |
3774 | @noindent |
3775 | The return status when listing options is zero if all @var{optnames} | |
3776 | are enabled, non-zero otherwise. | |
3777 | When setting or unsetting options, the return status is zero unless an | |
3778 | @var{optname} is not a valid shell option. | |
ccc6cda3 | 3779 | |
bb70624e JA |
3780 | @item source |
3781 | @btindex source | |
3782 | @example | |
3783 | source @var{filename} | |
3784 | @end example | |
3785 | A synonym for @code{.} (@pxref{Bourne Shell Builtins}). | |
ccc6cda3 | 3786 | |
bb70624e JA |
3787 | @item type |
3788 | @btindex type | |
3789 | @example | |
7117c2d2 | 3790 | type [-afptP] [@var{name} @dots{}] |
bb70624e JA |
3791 | @end example |
3792 | For each @var{name}, indicate how it would be interpreted if used as a | |
3793 | command name. | |
ccc6cda3 | 3794 | |
28ef6c31 | 3795 | If the @option{-t} option is used, @code{type} prints a single word |
bb70624e JA |
3796 | which is one of @samp{alias}, @samp{function}, @samp{builtin}, |
3797 | @samp{file} or @samp{keyword}, | |
3798 | if @var{name} is an alias, shell function, shell builtin, | |
3799 | disk file, or shell reserved word, respectively. | |
3800 | If the @var{name} is not found, then nothing is printed, and | |
3801 | @code{type} returns a failure status. | |
ccc6cda3 | 3802 | |
28ef6c31 JA |
3803 | If the @option{-p} option is used, @code{type} either returns the name |
3804 | of the disk file that would be executed, or nothing if @option{-t} | |
bb70624e JA |
3805 | would not return @samp{file}. |
3806 | ||
7117c2d2 JA |
3807 | The @option{-P} option forces a path search for each @var{name}, even if |
3808 | @option{-t} would not return @samp{file}. | |
3809 | ||
3810 | If a command is hashed, @option{-p} and @option{-P} print the hashed value, | |
3811 | not necessarily the file that appears first in @code{$PATH}. | |
3812 | ||
28ef6c31 | 3813 | If the @option{-a} option is used, @code{type} returns all of the places |
bb70624e | 3814 | that contain an executable named @var{file}. |
28ef6c31 | 3815 | This includes aliases and functions, if and only if the @option{-p} option |
bb70624e JA |
3816 | is not also used. |
3817 | ||
7117c2d2 JA |
3818 | If the @option{-f} option is used, @code{type} does not attempt to find |
3819 | shell functions, as with the @code{command} builtin. | |
3820 | ||
bb70624e JA |
3821 | The return status is zero if any of the @var{names} are found, non-zero |
3822 | if none are found. | |
ccc6cda3 | 3823 | |
bb70624e JA |
3824 | @item typeset |
3825 | @btindex typeset | |
ccc6cda3 | 3826 | @example |
b80f6443 | 3827 | typeset [-afFrxi] [-p] [@var{name}[=@var{value}] @dots{}] |
ccc6cda3 | 3828 | @end example |
bb70624e JA |
3829 | The @code{typeset} command is supplied for compatibility with the Korn |
3830 | shell; however, it has been deprecated in favor of the @code{declare} | |
3831 | builtin command. | |
ccc6cda3 | 3832 | |
bb70624e JA |
3833 | @item ulimit |
3834 | @btindex ulimit | |
3835 | @example | |
0628567a | 3836 | ulimit [-acdefilmnpqrstuvxSH] [@var{limit}] |
bb70624e JA |
3837 | @end example |
3838 | @code{ulimit} provides control over the resources available to processes | |
3839 | started by the shell, on systems that allow such control. If an | |
3840 | option is given, it is interpreted as follows: | |
ccc6cda3 | 3841 | @table @code |
bb70624e JA |
3842 | @item -S |
3843 | Change and report the soft limit associated with a resource. | |
ccc6cda3 | 3844 | |
bb70624e JA |
3845 | @item -H |
3846 | Change and report the hard limit associated with a resource. | |
ccc6cda3 | 3847 | |
bb70624e JA |
3848 | @item -a |
3849 | All current limits are reported. | |
ccc6cda3 | 3850 | |
bb70624e JA |
3851 | @item -c |
3852 | The maximum size of core files created. | |
ccc6cda3 | 3853 | |
bb70624e JA |
3854 | @item -d |
3855 | The maximum size of a process's data segment. | |
ccc6cda3 | 3856 | |
0628567a JA |
3857 | @item -e |
3858 | The maximum scheduling priority ("nice"). | |
3859 | ||
bb70624e | 3860 | @item -f |
0628567a JA |
3861 | The maximum size of files written by the shell and its children. |
3862 | ||
3863 | @item -i | |
3864 | The maximum number of pending signals. | |
ccc6cda3 | 3865 | |
bb70624e JA |
3866 | @item -l |
3867 | The maximum size that may be locked into memory. | |
ccc6cda3 | 3868 | |
bb70624e JA |
3869 | @item -m |
3870 | The maximum resident set size. | |
ccc6cda3 | 3871 | |
bb70624e JA |
3872 | @item -n |
3873 | The maximum number of open file descriptors. | |
ccc6cda3 | 3874 | |
bb70624e JA |
3875 | @item -p |
3876 | The pipe buffer size. | |
ccc6cda3 | 3877 | |
0628567a JA |
3878 | @item -q |
3879 | The maximum number of bytes in POSIX message queues. | |
3880 | ||
3881 | @item -r | |
3882 | The maximum real-time scheduling priority. | |
3883 | ||
bb70624e JA |
3884 | @item -s |
3885 | The maximum stack size. | |
ccc6cda3 | 3886 | |
bb70624e JA |
3887 | @item -t |
3888 | The maximum amount of cpu time in seconds. | |
ccc6cda3 | 3889 | |
bb70624e JA |
3890 | @item -u |
3891 | The maximum number of processes available to a single user. | |
ccc6cda3 | 3892 | |
bb70624e JA |
3893 | @item -v |
3894 | The maximum amount of virtual memory available to the process. | |
ccc6cda3 | 3895 | |
0628567a JA |
3896 | @item -x |
3897 | The maximum number of file locks. | |
3898 | ||
bb70624e | 3899 | @end table |
ccc6cda3 | 3900 | |
f73dda09 JA |
3901 | If @var{limit} is given, it is the new value of the specified resource; |
3902 | the special @var{limit} values @code{hard}, @code{soft}, and | |
3903 | @code{unlimited} stand for the current hard limit, the current soft limit, | |
3904 | and no limit, respectively. | |
bb70624e | 3905 | Otherwise, the current value of the soft limit for the specified resource |
28ef6c31 JA |
3906 | is printed, unless the @option{-H} option is supplied. |
3907 | When setting new limits, if neither @option{-H} nor @option{-S} is supplied, | |
bb70624e | 3908 | both the hard and soft limits are set. |
28ef6c31 JA |
3909 | If no option is given, then @option{-f} is assumed. Values are in 1024-byte |
3910 | increments, except for @option{-t}, which is in seconds, @option{-p}, | |
3911 | which is in units of 512-byte blocks, and @option{-n} and @option{-u}, which | |
bb70624e | 3912 | are unscaled values. |
ccc6cda3 | 3913 | |
f73dda09 JA |
3914 | The return status is zero unless an invalid option or argument is supplied, |
3915 | or an error occurs while setting a new limit. | |
ccc6cda3 | 3916 | |
bb70624e JA |
3917 | @item unalias |
3918 | @btindex unalias | |
3919 | @example | |
3920 | unalias [-a] [@var{name} @dots{} ] | |
3921 | @end example | |
ccc6cda3 | 3922 | |
28ef6c31 | 3923 | Remove each @var{name} from the list of aliases. If @option{-a} is |
bb70624e JA |
3924 | supplied, all aliases are removed. |
3925 | Aliases are described in @ref{Aliases}. | |
cce855bc | 3926 | |
ccc6cda3 JA |
3927 | @end table |
3928 | ||
bb70624e JA |
3929 | @node The Set Builtin |
3930 | @section The Set Builtin | |
ccc6cda3 | 3931 | |
bb70624e | 3932 | This builtin is so complicated that it deserves its own section. |
ccc6cda3 | 3933 | |
bb70624e JA |
3934 | @table @code |
3935 | @item set | |
3936 | @btindex set | |
3937 | @example | |
3938 | set [--abefhkmnptuvxBCHP] [-o @var{option}] [@var{argument} @dots{}] | |
3939 | @end example | |
ccc6cda3 | 3940 | |
bb70624e JA |
3941 | If no options or arguments are supplied, @code{set} displays the names |
3942 | and values of all shell variables and functions, sorted according to the | |
95732b49 JA |
3943 | current locale, in a format that may be reused as input |
3944 | for setting or resetting the currently-set variables. | |
3945 | Read-only variables cannot be reset. | |
3946 | In @sc{posix} mode, only shell variables are listed. | |
ccc6cda3 | 3947 | |
bb70624e JA |
3948 | When options are supplied, they set or unset shell attributes. |
3949 | Options, if specified, have the following meanings: | |
ccc6cda3 | 3950 | |
bb70624e JA |
3951 | @table @code |
3952 | @item -a | |
28ef6c31 JA |
3953 | Mark variables and function which are modified or created for export |
3954 | to the environment of subsequent commands. | |
ccc6cda3 | 3955 | |
bb70624e JA |
3956 | @item -b |
3957 | Cause the status of terminated background jobs to be reported | |
3958 | immediately, rather than before printing the next primary prompt. | |
ccc6cda3 | 3959 | |
bb70624e JA |
3960 | @item -e |
3961 | Exit immediately if a simple command (@pxref{Simple Commands}) exits | |
b80f6443 JA |
3962 | with a non-zero status, unless the command that fails is part of the |
3963 | command list immediately following a @code{while} or @code{until} | |
3964 | keyword, part of the test in an @code{if} statement, | |
bb70624e JA |
3965 | part of a @code{&&} or @code{||} list, or if the command's return |
3966 | status is being inverted using @code{!}. | |
f73dda09 | 3967 | A trap on @code{ERR}, if set, is executed before the shell exits. |
ccc6cda3 | 3968 | |
bb70624e JA |
3969 | @item -f |
3970 | Disable file name generation (globbing). | |
ccc6cda3 | 3971 | |
bb70624e JA |
3972 | @item -h |
3973 | Locate and remember (hash) commands as they are looked up for execution. | |
3974 | This option is enabled by default. | |
ccc6cda3 | 3975 | |
bb70624e JA |
3976 | @item -k |
3977 | All arguments in the form of assignment statements are placed | |
3978 | in the environment for a command, not just those that precede | |
3979 | the command name. | |
ccc6cda3 | 3980 | |
bb70624e JA |
3981 | @item -m |
3982 | Job control is enabled (@pxref{Job Control}). | |
ccc6cda3 | 3983 | |
bb70624e JA |
3984 | @item -n |
3985 | Read commands but do not execute them; this may be used to check a | |
3986 | script for syntax errors. | |
3987 | This option is ignored by interactive shells. | |
b72432fd | 3988 | |
bb70624e | 3989 | @item -o @var{option-name} |
ccc6cda3 | 3990 | |
bb70624e | 3991 | Set the option corresponding to @var{option-name}: |
ccc6cda3 | 3992 | |
bb70624e JA |
3993 | @table @code |
3994 | @item allexport | |
3995 | Same as @code{-a}. | |
ccc6cda3 | 3996 | |
bb70624e JA |
3997 | @item braceexpand |
3998 | Same as @code{-B}. | |
ccc6cda3 | 3999 | |
bb70624e JA |
4000 | @item emacs |
4001 | Use an @code{emacs}-style line editing interface (@pxref{Command Line Editing}). | |
d166f048 | 4002 | |
bb70624e JA |
4003 | @item errexit |
4004 | Same as @code{-e}. | |
d166f048 | 4005 | |
b80f6443 JA |
4006 | @item errtrace |
4007 | Same as @code{-E}. | |
4008 | ||
4009 | @item functrace | |
4010 | Same as @code{-T}. | |
4011 | ||
bb70624e JA |
4012 | @item hashall |
4013 | Same as @code{-h}. | |
ccc6cda3 | 4014 | |
bb70624e JA |
4015 | @item histexpand |
4016 | Same as @code{-H}. | |
ccc6cda3 | 4017 | |
bb70624e JA |
4018 | @item history |
4019 | Enable command history, as described in @ref{Bash History Facilities}. | |
4020 | This option is on by default in interactive shells. | |
ccc6cda3 | 4021 | |
bb70624e JA |
4022 | @item ignoreeof |
4023 | An interactive shell will not exit upon reading EOF. | |
ccc6cda3 | 4024 | |
bb70624e JA |
4025 | @item keyword |
4026 | Same as @code{-k}. | |
ccc6cda3 | 4027 | |
bb70624e JA |
4028 | @item monitor |
4029 | Same as @code{-m}. | |
ccc6cda3 | 4030 | |
bb70624e JA |
4031 | @item noclobber |
4032 | Same as @code{-C}. | |
ccc6cda3 | 4033 | |
bb70624e JA |
4034 | @item noexec |
4035 | Same as @code{-n}. | |
ccc6cda3 | 4036 | |
bb70624e JA |
4037 | @item noglob |
4038 | Same as @code{-f}. | |
ccc6cda3 | 4039 | |
f73dda09 JA |
4040 | @item nolog |
4041 | Currently ignored. | |
4042 | ||
bb70624e JA |
4043 | @item notify |
4044 | Same as @code{-b}. | |
ccc6cda3 | 4045 | |
bb70624e JA |
4046 | @item nounset |
4047 | Same as @code{-u}. | |
ccc6cda3 | 4048 | |
bb70624e JA |
4049 | @item onecmd |
4050 | Same as @code{-t}. | |
ccc6cda3 | 4051 | |
bb70624e JA |
4052 | @item physical |
4053 | Same as @code{-P}. | |
ccc6cda3 | 4054 | |
b80f6443 JA |
4055 | @item pipefail |
4056 | If set, the return value of a pipeline is the value of the last | |
4057 | (rightmost) command to exit with a non-zero status, or zero if all | |
4058 | commands in the pipeline exit successfully. | |
4059 | This option is disabled by default. | |
4060 | ||
bb70624e JA |
4061 | @item posix |
4062 | Change the behavior of Bash where the default operation differs | |
0628567a | 4063 | from the @sc{posix} standard to match the standard |
bb70624e JA |
4064 | (@pxref{Bash POSIX Mode}). |
4065 | This is intended to make Bash behave as a strict superset of that | |
4066 | standard. | |
ccc6cda3 | 4067 | |
bb70624e JA |
4068 | @item privileged |
4069 | Same as @code{-p}. | |
cce855bc | 4070 | |
bb70624e JA |
4071 | @item verbose |
4072 | Same as @code{-v}. | |
ccc6cda3 | 4073 | |
bb70624e JA |
4074 | @item vi |
4075 | Use a @code{vi}-style line editing interface. | |
ccc6cda3 | 4076 | |
bb70624e JA |
4077 | @item xtrace |
4078 | Same as @code{-x}. | |
ccc6cda3 JA |
4079 | @end table |
4080 | ||
bb70624e JA |
4081 | @item -p |
4082 | Turn on privileged mode. | |
28ef6c31 | 4083 | In this mode, the @env{$BASH_ENV} and @env{$ENV} files are not |
bb70624e | 4084 | processed, shell functions are not inherited from the environment, |
28ef6c31 | 4085 | and the @env{SHELLOPTS} variable, if it appears in the environment, |
bb70624e JA |
4086 | is ignored. |
4087 | If the shell is started with the effective user (group) id not equal to the | |
4088 | real user (group) id, and the @code{-p} option is not supplied, these actions | |
4089 | are taken and the effective user id is set to the real user id. | |
4090 | If the @code{-p} option is supplied at startup, the effective user id is | |
4091 | not reset. | |
4092 | Turning this option off causes the effective user | |
4093 | and group ids to be set to the real user and group ids. | |
cce855bc | 4094 | |
bb70624e JA |
4095 | @item -t |
4096 | Exit after reading and executing one command. | |
ccc6cda3 | 4097 | |
bb70624e JA |
4098 | @item -u |
4099 | Treat unset variables as an error when performing parameter expansion. | |
4100 | An error message will be written to the standard error, and a non-interactive | |
4101 | shell will exit. | |
ccc6cda3 | 4102 | |
bb70624e JA |
4103 | @item -v |
4104 | Print shell input lines as they are read. | |
ccc6cda3 | 4105 | |
bb70624e | 4106 | @item -x |
0628567a JA |
4107 | Print a trace of simple commands, @code{for} commands, @code{case} |
4108 | commands, @code{select} commands, and arithmetic @code{for} commands | |
b80f6443 JA |
4109 | and their arguments or associated word lists after they are |
4110 | expanded and before they are executed. The value of the @env{PS4} | |
4111 | variable is expanded and the resultant value is printed before | |
4112 | the command and its expanded arguments. | |
ccc6cda3 | 4113 | |
bb70624e JA |
4114 | @item -B |
4115 | The shell will perform brace expansion (@pxref{Brace Expansion}). | |
4116 | This option is on by default. | |
ccc6cda3 | 4117 | |
bb70624e JA |
4118 | @item -C |
4119 | Prevent output redirection using @samp{>}, @samp{>&}, and @samp{<>} | |
4120 | from overwriting existing files. | |
ccc6cda3 | 4121 | |
b80f6443 JA |
4122 | @item -E |
4123 | If set, any trap on @code{ERR} is inherited by shell functions, command | |
4124 | substitutions, and commands executed in a subshell environment. | |
4125 | The @code{ERR} trap is normally not inherited in such cases. | |
4126 | ||
bb70624e JA |
4127 | @item -H |
4128 | Enable @samp{!} style history substitution (@pxref{History Interaction}). | |
4129 | This option is on by default for interactive shells. | |
ccc6cda3 | 4130 | |
bb70624e JA |
4131 | @item -P |
4132 | If set, do not follow symbolic links when performing commands such as | |
4133 | @code{cd} which change the current directory. The physical directory | |
4134 | is used instead. By default, Bash follows | |
4135 | the logical chain of directories when performing commands | |
4136 | which change the current directory. | |
ccc6cda3 | 4137 | |
bb70624e JA |
4138 | For example, if @file{/usr/sys} is a symbolic link to @file{/usr/local/sys} |
4139 | then: | |
4140 | @example | |
4141 | $ cd /usr/sys; echo $PWD | |
4142 | /usr/sys | |
4143 | $ cd ..; pwd | |
4144 | /usr | |
4145 | @end example | |
ccc6cda3 | 4146 | |
bb70624e JA |
4147 | @noindent |
4148 | If @code{set -P} is on, then: | |
4149 | @example | |
4150 | $ cd /usr/sys; echo $PWD | |
4151 | /usr/local/sys | |
4152 | $ cd ..; pwd | |
4153 | /usr/local | |
4154 | @end example | |
ccc6cda3 | 4155 | |
b80f6443 | 4156 | @item -T |
95732b49 JA |
4157 | If set, any trap on @code{DEBUG} and @code{RETURN} are inherited by |
4158 | shell functions, command substitutions, and commands executed | |
4159 | in a subshell environment. | |
4160 | The @code{DEBUG} and @code{RETURN} traps are normally not inherited | |
4161 | in such cases. | |
b80f6443 | 4162 | |
bb70624e JA |
4163 | @item -- |
4164 | If no arguments follow this option, then the positional parameters are | |
4165 | unset. Otherwise, the positional parameters are set to the | |
4166 | @var{arguments}, even if some of them begin with a @samp{-}. | |
4167 | ||
4168 | @item - | |
4169 | Signal the end of options, cause all remaining @var{arguments} | |
28ef6c31 JA |
4170 | to be assigned to the positional parameters. The @option{-x} |
4171 | and @option{-v} options are turned off. | |
bb70624e | 4172 | If there are no arguments, the positional parameters remain unchanged. |
ccc6cda3 JA |
4173 | @end table |
4174 | ||
bb70624e JA |
4175 | Using @samp{+} rather than @samp{-} causes these options to be |
4176 | turned off. The options can also be used upon invocation of the | |
4177 | shell. The current set of options may be found in @code{$-}. | |
cce855bc | 4178 | |
bb70624e JA |
4179 | The remaining N @var{arguments} are positional parameters and are |
4180 | assigned, in order, to @code{$1}, @code{$2}, @dots{} @code{$N}. | |
4181 | The special parameter @code{#} is set to N. | |
ccc6cda3 | 4182 | |
bb70624e | 4183 | The return status is always zero unless an invalid option is supplied. |
ccc6cda3 JA |
4184 | @end table |
4185 | ||
bb70624e JA |
4186 | @node Special Builtins |
4187 | @section Special Builtins | |
4188 | @cindex special builtin | |
cce855bc | 4189 | |
0628567a | 4190 | For historical reasons, the @sc{posix} standard has classified |
bb70624e JA |
4191 | several builtin commands as @emph{special}. |
4192 | When Bash is executing in @sc{posix} mode, the special builtins | |
4193 | differ from other builtin commands in three respects: | |
ccc6cda3 | 4194 | |
bb70624e JA |
4195 | @enumerate |
4196 | @item | |
4197 | Special builtins are found before shell functions during command lookup. | |
cce855bc | 4198 | |
bb70624e JA |
4199 | @item |
4200 | If a special builtin returns an error status, a non-interactive shell exits. | |
cce855bc | 4201 | |
bb70624e JA |
4202 | @item |
4203 | Assignment statements preceding the command stay in effect in the shell | |
4204 | environment after the command completes. | |
4205 | @end enumerate | |
ccc6cda3 | 4206 | |
bb70624e JA |
4207 | When Bash is not executing in @sc{posix} mode, these builtins behave no |
4208 | differently than the rest of the Bash builtin commands. | |
4209 | The Bash @sc{posix} mode is described in @ref{Bash POSIX Mode}. | |
ccc6cda3 | 4210 | |
bb70624e | 4211 | These are the @sc{posix} special builtins: |
ccc6cda3 | 4212 | @example |
bb70624e JA |
4213 | @w{break : . continue eval exec exit export readonly return set} |
4214 | @w{shift trap unset} | |
ccc6cda3 | 4215 | @end example |
ccc6cda3 | 4216 | |
bb70624e JA |
4217 | @node Shell Variables |
4218 | @chapter Shell Variables | |
cce855bc | 4219 | |
bb70624e JA |
4220 | @menu |
4221 | * Bourne Shell Variables:: Variables which Bash uses in the same way | |
4222 | as the Bourne Shell. | |
4223 | * Bash Variables:: List of variables that exist in Bash. | |
4224 | @end menu | |
cce855bc | 4225 | |
bb70624e JA |
4226 | This chapter describes the shell variables that Bash uses. |
4227 | Bash automatically assigns default values to a number of variables. | |
ccc6cda3 | 4228 | |
bb70624e JA |
4229 | @node Bourne Shell Variables |
4230 | @section Bourne Shell Variables | |
ccc6cda3 | 4231 | |
bb70624e JA |
4232 | Bash uses certain shell variables in the same way as the Bourne shell. |
4233 | In some cases, Bash assigns a default value to the variable. | |
ccc6cda3 | 4234 | |
bb70624e | 4235 | @vtable @code |
ccc6cda3 | 4236 | |
bb70624e JA |
4237 | @item CDPATH |
4238 | A colon-separated list of directories used as a search path for | |
4239 | the @code{cd} builtin command. | |
ccc6cda3 | 4240 | |
bb70624e JA |
4241 | @item HOME |
4242 | The current user's home directory; the default for the @code{cd} builtin | |
4243 | command. | |
4244 | The value of this variable is also used by tilde expansion | |
4245 | (@pxref{Tilde Expansion}). | |
ccc6cda3 | 4246 | |
bb70624e JA |
4247 | @item IFS |
4248 | A list of characters that separate fields; used when the shell splits | |
4249 | words as part of expansion. | |
ccc6cda3 | 4250 | |
bb70624e | 4251 | @item MAIL |
28ef6c31 | 4252 | If this parameter is set to a filename and the @env{MAILPATH} variable |
bb70624e JA |
4253 | is not set, Bash informs the user of the arrival of mail in |
4254 | the specified file. | |
ccc6cda3 | 4255 | |
bb70624e JA |
4256 | @item MAILPATH |
4257 | A colon-separated list of filenames which the shell periodically checks | |
4258 | for new mail. | |
4259 | Each list entry can specify the message that is printed when new mail | |
4260 | arrives in the mail file by separating the file name from the message with | |
4261 | a @samp{?}. | |
4262 | When used in the text of the message, @code{$_} expands to the name of | |
4263 | the current mail file. | |
ccc6cda3 | 4264 | |
bb70624e JA |
4265 | @item OPTARG |
4266 | The value of the last option argument processed by the @code{getopts} builtin. | |
ccc6cda3 | 4267 | |
bb70624e JA |
4268 | @item OPTIND |
4269 | The index of the last option argument processed by the @code{getopts} builtin. | |
ccc6cda3 | 4270 | |
bb70624e JA |
4271 | @item PATH |
4272 | A colon-separated list of directories in which the shell looks for | |
4273 | commands. | |
b80f6443 JA |
4274 | A zero-length (null) directory name in the value of @code{PATH} indicates the |
4275 | current directory. | |
4276 | A null directory name may appear as two adjacent colons, or as an initial | |
4277 | or trailing colon. | |
4278 | ||
ccc6cda3 | 4279 | |
bb70624e JA |
4280 | @item PS1 |
4281 | The primary prompt string. The default value is @samp{\s-\v\$ }. | |
4282 | @xref{Printing a Prompt}, for the complete list of escape | |
28ef6c31 | 4283 | sequences that are expanded before @env{PS1} is displayed. |
ccc6cda3 | 4284 | |
bb70624e JA |
4285 | @item PS2 |
4286 | The secondary prompt string. The default value is @samp{> }. | |
ccc6cda3 | 4287 | |
bb70624e | 4288 | @end vtable |
ccc6cda3 | 4289 | |
bb70624e JA |
4290 | @node Bash Variables |
4291 | @section Bash Variables | |
ccc6cda3 | 4292 | |
bb70624e JA |
4293 | These variables are set or used by Bash, but other shells |
4294 | do not normally treat them specially. | |
ccc6cda3 | 4295 | |
bb70624e JA |
4296 | A few variables used by Bash are described in different chapters: |
4297 | variables for controlling the job control facilities | |
4298 | (@pxref{Job Control Variables}). | |
ccc6cda3 | 4299 | |
bb70624e | 4300 | @vtable @code |
cce855bc | 4301 | |
bb70624e JA |
4302 | @item BASH |
4303 | The full pathname used to execute the current instance of Bash. | |
cce855bc | 4304 | |
b80f6443 JA |
4305 | @item BASH_ARGC |
4306 | An array variable whose values are the number of parameters in each | |
4307 | frame of the current bash execution call stack. The number of | |
4308 | parameters to the current subroutine (shell function or script executed | |
4309 | with @code{.} or @code{source}) is at the top of the stack. When a | |
4310 | subroutine is executed, the number of parameters passed is pushed onto | |
4311 | @code{BASH_ARGC}. | |
95732b49 JA |
4312 | The shell sets @code{BASH_ARGC} only when in extended debugging mode |
4313 | (see @ref{Bash Builtins} | |
4314 | for a description of the @code{extdebug} option to the @code{shopt} | |
4315 | builtin). | |
b80f6443 JA |
4316 | |
4317 | @item BASH_ARGV | |
4318 | An array variable containing all of the parameters in the current bash | |
4319 | execution call stack. The final parameter of the last subroutine call | |
4320 | is at the top of the stack; the first parameter of the initial call is | |
4321 | at the bottom. When a subroutine is executed, the parameters supplied | |
4322 | are pushed onto @code{BASH_ARGV}. | |
95732b49 JA |
4323 | The shell sets @code{BASH_ARGV} only when in extended debugging mode |
4324 | (see @ref{Bash Builtins} | |
4325 | for a description of the @code{extdebug} option to the @code{shopt} | |
4326 | builtin). | |
b80f6443 JA |
4327 | |
4328 | @item BASH_COMMAND | |
4329 | The command currently being executed or about to be executed, unless the | |
4330 | shell is executing a command as the result of a trap, | |
4331 | in which case it is the command executing at the time of the trap. | |
4332 | ||
bb70624e JA |
4333 | @item BASH_ENV |
4334 | If this variable is set when Bash is invoked to execute a shell | |
4335 | script, its value is expanded and used as the name of a startup file | |
4336 | to read before executing the script. @xref{Bash Startup Files}. | |
ccc6cda3 | 4337 | |
b80f6443 JA |
4338 | @item BASH_EXECUTION_STRING |
4339 | The command argument to the @option{-c} invocation option. | |
4340 | ||
4341 | @item BASH_LINENO | |
4342 | An array variable whose members are the line numbers in source files | |
4343 | corresponding to each member of @var{FUNCNAME}. | |
4344 | @code{$@{BASH_LINENO[$i]@}} is the line number in the source file where | |
95732b49 JA |
4345 | @code{$@{FUNCNAME[$i]@}} was called. |
4346 | The corresponding source file name is @code{$@{BASH_SOURCE[$i]@}}. | |
b80f6443 JA |
4347 | Use @code{LINENO} to obtain the current line number. |
4348 | ||
4349 | @item BASH_REMATCH | |
4350 | An array variable whose members are assigned by the @samp{=~} binary | |
4351 | operator to the @code{[[} conditional command | |
4352 | (@pxref{Conditional Constructs}). | |
4353 | The element with index 0 is the portion of the string | |
4354 | matching the entire regular expression. | |
4355 | The element with index @var{n} is the portion of the | |
4356 | string matching the @var{n}th parenthesized subexpression. | |
4357 | This variable is read-only. | |
4358 | ||
4359 | @item BASH_SOURCE | |
4360 | An array variable whose members are the source filenames corresponding | |
4361 | to the elements in the @code{FUNCNAME} array variable. | |
4362 | ||
4363 | @item BASH_SUBSHELL | |
4364 | Incremented by one each time a subshell or subshell environment is spawned. | |
4365 | The initial value is 0. | |
ccc6cda3 | 4366 | |
bb70624e JA |
4367 | @item BASH_VERSINFO |
4368 | A readonly array variable (@pxref{Arrays}) | |
4369 | whose members hold version information for this instance of Bash. | |
4370 | The values assigned to the array members are as follows: | |
ccc6cda3 | 4371 | |
bb70624e | 4372 | @table @code |
ccc6cda3 | 4373 | |
bb70624e JA |
4374 | @item BASH_VERSINFO[0] |
4375 | The major version number (the @var{release}). | |
cce855bc | 4376 | |
bb70624e JA |
4377 | @item BASH_VERSINFO[1] |
4378 | The minor version number (the @var{version}). | |
ccc6cda3 | 4379 | |
bb70624e JA |
4380 | @item BASH_VERSINFO[2] |
4381 | The patch level. | |
ccc6cda3 | 4382 | |
bb70624e JA |
4383 | @item BASH_VERSINFO[3] |
4384 | The build version. | |
ccc6cda3 | 4385 | |
bb70624e JA |
4386 | @item BASH_VERSINFO[4] |
4387 | The release status (e.g., @var{beta1}). | |
cce855bc | 4388 | |
bb70624e | 4389 | @item BASH_VERSINFO[5] |
28ef6c31 | 4390 | The value of @env{MACHTYPE}. |
ccc6cda3 | 4391 | |
bb70624e | 4392 | @end table |
ccc6cda3 | 4393 | |
b80f6443 JA |
4394 | @item BASH_VERSION |
4395 | The version number of the current instance of Bash. | |
4396 | ||
f73dda09 JA |
4397 | @item COLUMNS |
4398 | Used by the @code{select} builtin command to determine the terminal width | |
4399 | when printing selection lists. Automatically set upon receipt of a | |
4400 | @code{SIGWINCH}. | |
bb70624e JA |
4401 | |
4402 | @item COMP_CWORD | |
28ef6c31 | 4403 | An index into @env{$@{COMP_WORDS@}} of the word containing the current |
bb70624e JA |
4404 | cursor position. |
4405 | This variable is available only in shell functions invoked by the | |
4406 | programmable completion facilities (@pxref{Programmable Completion}). | |
4407 | ||
4408 | @item COMP_LINE | |
4409 | The current command line. | |
4410 | This variable is available only in shell functions and external | |
4411 | commands invoked by the | |
4412 | programmable completion facilities (@pxref{Programmable Completion}). | |
4413 | ||
4414 | @item COMP_POINT | |
4415 | The index of the current cursor position relative to the beginning of | |
4416 | the current command. | |
4417 | If the current cursor position is at the end of the current command, | |
4418 | the value of this variable is equal to @code{$@{#COMP_LINE@}}. | |
4419 | This variable is available only in shell functions and external | |
4420 | commands invoked by the | |
4421 | programmable completion facilities (@pxref{Programmable Completion}). | |
4422 | ||
b80f6443 JA |
4423 | @item COMP_WORDBREAKS |
4424 | The set of characters that the Readline library treats as word | |
4425 | separators when performing word completion. | |
4426 | If @code{COMP_WORDBREAKS} is unset, it loses its special properties, | |
4427 | even if it is subsequently reset. | |
4428 | ||
f73dda09 JA |
4429 | @item COMP_WORDS |
4430 | An array variable consisting of the individual | |
4431 | words in the current command line. | |
0628567a JA |
4432 | The words are split on shell metacharacters as the shell parser would |
4433 | separate them. | |
f73dda09 JA |
4434 | This variable is available only in shell functions invoked by the |
4435 | programmable completion facilities (@pxref{Programmable Completion}). | |
4436 | ||
bb70624e JA |
4437 | @item COMPREPLY |
4438 | An array variable from which Bash reads the possible completions | |
4439 | generated by a shell function invoked by the programmable completion | |
4440 | facility (@pxref{Programmable Completion}). | |
b72432fd | 4441 | |
bb70624e JA |
4442 | @item DIRSTACK |
4443 | An array variable containing the current contents of the directory stack. | |
4444 | Directories appear in the stack in the order they are displayed by the | |
4445 | @code{dirs} builtin. | |
4446 | Assigning to members of this array variable may be used to modify | |
4447 | directories already in the stack, but the @code{pushd} and @code{popd} | |
4448 | builtins must be used to add and remove directories. | |
4449 | Assignment to this variable will not change the current directory. | |
28ef6c31 | 4450 | If @env{DIRSTACK} is unset, it loses its special properties, even if |
bb70624e | 4451 | it is subsequently reset. |
ccc6cda3 | 4452 | |
b80f6443 JA |
4453 | @item EMACS |
4454 | If Bash finds this variable in the environment when the shell | |
4455 | starts with value @samp{t}, it assumes that the shell is running in an | |
4456 | emacs shell buffer and disables line editing. | |
4457 | ||
bb70624e JA |
4458 | @item EUID |
4459 | The numeric effective user id of the current user. This variable | |
4460 | is readonly. | |
ccc6cda3 | 4461 | |
bb70624e | 4462 | @item FCEDIT |
28ef6c31 | 4463 | The editor used as a default by the @option{-e} option to the @code{fc} |
bb70624e | 4464 | builtin command. |
cce855bc | 4465 | |
bb70624e JA |
4466 | @item FIGNORE |
4467 | A colon-separated list of suffixes to ignore when performing | |
4468 | filename completion. | |
4469 | A file name whose suffix matches one of the entries in | |
28ef6c31 | 4470 | @env{FIGNORE} |
bb70624e JA |
4471 | is excluded from the list of matched file names. A sample |
4472 | value is @samp{.o:~} | |
cce855bc | 4473 | |
f73dda09 | 4474 | @item FUNCNAME |
b80f6443 JA |
4475 | An array variable containing the names of all shell functions |
4476 | currently in the execution call stack. | |
4477 | The element with index 0 is the name of any currently-executing | |
4478 | shell function. | |
4479 | The bottom-most element is "main". | |
f73dda09 JA |
4480 | This variable exists only when a shell function is executing. |
4481 | Assignments to @env{FUNCNAME} have no effect and return an error status. | |
4482 | If @env{FUNCNAME} is unset, it loses its special properties, even if | |
4483 | it is subsequently reset. | |
4484 | ||
bb70624e JA |
4485 | @item GLOBIGNORE |
4486 | A colon-separated list of patterns defining the set of filenames to | |
4487 | be ignored by filename expansion. | |
4488 | If a filename matched by a filename expansion pattern also matches one | |
28ef6c31 | 4489 | of the patterns in @env{GLOBIGNORE}, it is removed from the list |
bb70624e | 4490 | of matches. |
ccc6cda3 | 4491 | |
bb70624e JA |
4492 | @item GROUPS |
4493 | An array variable containing the list of groups of which the current | |
4494 | user is a member. | |
28ef6c31 JA |
4495 | Assignments to @env{GROUPS} have no effect and return an error status. |
4496 | If @env{GROUPS} is unset, it loses its special properties, even if it is | |
bb70624e | 4497 | subsequently reset. |
ccc6cda3 | 4498 | |
bb70624e JA |
4499 | @item histchars |
4500 | Up to three characters which control history expansion, quick | |
4501 | substitution, and tokenization (@pxref{History Interaction}). | |
4502 | The first character is the | |
4503 | @var{history expansion} character, that is, the character which signifies the | |
4504 | start of a history expansion, normally @samp{!}. The second character is the | |
4505 | character which signifies `quick substitution' when seen as the first | |
4506 | character on a line, normally @samp{^}. The optional third character is the | |
4507 | character which indicates that the remainder of the line is a comment when | |
4508 | found as the first character of a word, usually @samp{#}. The history | |
4509 | comment character causes history substitution to be skipped for the | |
4510 | remaining words on the line. It does not necessarily cause the shell | |
4511 | parser to treat the rest of the line as a comment. | |
ccc6cda3 | 4512 | |
bb70624e JA |
4513 | @item HISTCMD |
4514 | The history number, or index in the history list, of the current | |
28ef6c31 | 4515 | command. If @env{HISTCMD} is unset, it loses its special properties, |
bb70624e | 4516 | even if it is subsequently reset. |
ccc6cda3 | 4517 | |
bb70624e | 4518 | @item HISTCONTROL |
b80f6443 JA |
4519 | A colon-separated list of values controlling how commands are saved on |
4520 | the history list. | |
4521 | If the list of values includes @samp{ignorespace}, lines which begin | |
4522 | with a space character are not saved in the history list. | |
4523 | A value of @samp{ignoredups} causes lines which match the previous | |
4524 | history entry to not be saved. | |
4525 | A value of @samp{ignoreboth} is shorthand for | |
4526 | @samp{ignorespace} and @samp{ignoredups}. | |
4527 | A value of @samp{erasedups} causes all previous lines matching the | |
4528 | current line to be removed from the history list before that line | |
4529 | is saved. | |
4530 | Any value not in the above list is ignored. | |
4531 | If @env{HISTCONTROL} is unset, or does not include a valid value, | |
4532 | all lines read by the shell parser are saved on the history list, | |
4533 | subject to the value of @env{HISTIGNORE}. | |
bb70624e JA |
4534 | The second and subsequent lines of a multi-line compound command are |
4535 | not tested, and are added to the history regardless of the value of | |
28ef6c31 | 4536 | @env{HISTCONTROL}. |
ccc6cda3 | 4537 | |
f73dda09 JA |
4538 | @item HISTFILE |
4539 | The name of the file to which the command history is saved. The | |
4540 | default value is @file{~/.bash_history}. | |
4541 | ||
4542 | @item HISTFILESIZE | |
4543 | The maximum number of lines contained in the history file. When this | |
4544 | variable is assigned a value, the history file is truncated, if | |
0628567a JA |
4545 | necessary, by removing the oldest entries, |
4546 | to contain no more than that number of lines. | |
f73dda09 JA |
4547 | The history file is also truncated to this size after |
4548 | writing it when an interactive shell exits. | |
4549 | The default value is 500. | |
4550 | ||
bb70624e JA |
4551 | @item HISTIGNORE |
4552 | A colon-separated list of patterns used to decide which command | |
4553 | lines should be saved on the history list. Each pattern is | |
4554 | anchored at the beginning of the line and must match the complete | |
4555 | line (no implicit @samp{*} is appended). Each pattern is tested | |
28ef6c31 | 4556 | against the line after the checks specified by @env{HISTCONTROL} |
bb70624e JA |
4557 | are applied. In addition to the normal shell pattern matching |
4558 | characters, @samp{&} matches the previous history line. @samp{&} | |
4559 | may be escaped using a backslash; the backslash is removed | |
4560 | before attempting a match. | |
4561 | The second and subsequent lines of a multi-line compound command are | |
4562 | not tested, and are added to the history regardless of the value of | |
28ef6c31 | 4563 | @env{HISTIGNORE}. |
ccc6cda3 | 4564 | |
28ef6c31 | 4565 | @env{HISTIGNORE} subsumes the function of @env{HISTCONTROL}. A |
bb70624e JA |
4566 | pattern of @samp{&} is identical to @code{ignoredups}, and a |
4567 | pattern of @samp{[ ]*} is identical to @code{ignorespace}. | |
4568 | Combining these two patterns, separating them with a colon, | |
4569 | provides the functionality of @code{ignoreboth}. | |
ccc6cda3 | 4570 | |
bb70624e JA |
4571 | @item HISTSIZE |
4572 | The maximum number of commands to remember on the history list. | |
4573 | The default value is 500. | |
ccc6cda3 | 4574 | |
b80f6443 JA |
4575 | @item HISTTIMEFORMAT |
4576 | If this variable is set and not null, its value is used as a format string | |
4577 | for @var{strftime} to print the time stamp associated with each history | |
4578 | entry displayed by the @code{history} builtin. | |
4579 | If this variable is set, time stamps are written to the history file so | |
4580 | they may be preserved across shell sessions. | |
4581 | ||
bb70624e JA |
4582 | @item HOSTFILE |
4583 | Contains the name of a file in the same format as @file{/etc/hosts} that | |
4584 | should be read when the shell needs to complete a hostname. | |
4585 | The list of possible hostname completions may be changed while the shell | |
4586 | is running; | |
4587 | the next time hostname completion is attempted after the | |
4588 | value is changed, Bash adds the contents of the new file to the | |
4589 | existing list. | |
28ef6c31 | 4590 | If @env{HOSTFILE} is set, but has no value, Bash attempts to read |
bb70624e | 4591 | @file{/etc/hosts} to obtain the list of possible hostname completions. |
28ef6c31 | 4592 | When @env{HOSTFILE} is unset, the hostname list is cleared. |
ccc6cda3 | 4593 | |
bb70624e JA |
4594 | @item HOSTNAME |
4595 | The name of the current host. | |
ccc6cda3 | 4596 | |
bb70624e JA |
4597 | @item HOSTTYPE |
4598 | A string describing the machine Bash is running on. | |
ccc6cda3 | 4599 | |
bb70624e JA |
4600 | @item IGNOREEOF |
4601 | Controls the action of the shell on receipt of an @code{EOF} character | |
4602 | as the sole input. If set, the value denotes the number | |
4603 | of consecutive @code{EOF} characters that can be read as the | |
4604 | first character on an input line | |
4605 | before the shell will exit. If the variable exists but does not | |
4606 | have a numeric value (or has no value) then the default is 10. | |
4607 | If the variable does not exist, then @code{EOF} signifies the end of | |
4608 | input to the shell. This is only in effect for interactive shells. | |
ccc6cda3 | 4609 | |
bb70624e JA |
4610 | @item INPUTRC |
4611 | The name of the Readline initialization file, overriding the default | |
4612 | of @file{~/.inputrc}. | |
ccc6cda3 | 4613 | |
bb70624e JA |
4614 | @item LANG |
4615 | Used to determine the locale category for any category not specifically | |
4616 | selected with a variable starting with @code{LC_}. | |
ccc6cda3 | 4617 | |
bb70624e | 4618 | @item LC_ALL |
28ef6c31 | 4619 | This variable overrides the value of @env{LANG} and any other |
bb70624e | 4620 | @code{LC_} variable specifying a locale category. |
ccc6cda3 | 4621 | |
bb70624e JA |
4622 | @item LC_COLLATE |
4623 | This variable determines the collation order used when sorting the | |
4624 | results of filename expansion, and | |
4625 | determines the behavior of range expressions, equivalence classes, | |
4626 | and collating sequences within filename expansion and pattern matching | |
4627 | (@pxref{Filename Expansion}). | |
ccc6cda3 | 4628 | |
bb70624e JA |
4629 | @item LC_CTYPE |
4630 | This variable determines the interpretation of characters and the | |
4631 | behavior of character classes within filename expansion and pattern | |
4632 | matching (@pxref{Filename Expansion}). | |
ccc6cda3 | 4633 | |
bb70624e JA |
4634 | @item LC_MESSAGES |
4635 | This variable determines the locale used to translate double-quoted | |
4636 | strings preceded by a @samp{$} (@pxref{Locale Translation}). | |
ccc6cda3 | 4637 | |
bb70624e JA |
4638 | @item LC_NUMERIC |
4639 | This variable determines the locale category used for number formatting. | |
ccc6cda3 | 4640 | |
f73dda09 JA |
4641 | @item LINENO |
4642 | The line number in the script or shell function currently executing. | |
4643 | ||
28ef6c31 JA |
4644 | @item LINES |
4645 | Used by the @code{select} builtin command to determine the column length | |
4646 | for printing selection lists. Automatically set upon receipt of a | |
4647 | @code{SIGWINCH}. | |
4648 | ||
bb70624e JA |
4649 | @item MACHTYPE |
4650 | A string that fully describes the system type on which Bash | |
4651 | is executing, in the standard @sc{gnu} @var{cpu-company-system} format. | |
ccc6cda3 | 4652 | |
bb70624e JA |
4653 | @item MAILCHECK |
4654 | How often (in seconds) that the shell should check for mail in the | |
28ef6c31 JA |
4655 | files specified in the @env{MAILPATH} or @env{MAIL} variables. |
4656 | The default is 60 seconds. When it is time to check | |
4657 | for mail, the shell does so before displaying the primary prompt. | |
4658 | If this variable is unset, or set to a value that is not a number | |
4659 | greater than or equal to zero, the shell disables mail checking. | |
ccc6cda3 | 4660 | |
bb70624e JA |
4661 | @item OLDPWD |
4662 | The previous working directory as set by the @code{cd} builtin. | |
ccc6cda3 | 4663 | |
bb70624e JA |
4664 | @item OPTERR |
4665 | If set to the value 1, Bash displays error messages | |
4666 | generated by the @code{getopts} builtin command. | |
ccc6cda3 | 4667 | |
bb70624e JA |
4668 | @item OSTYPE |
4669 | A string describing the operating system Bash is running on. | |
cce855bc | 4670 | |
bb70624e JA |
4671 | @item PIPESTATUS |
4672 | An array variable (@pxref{Arrays}) | |
4673 | containing a list of exit status values from the processes | |
4674 | in the most-recently-executed foreground pipeline (which may | |
4675 | contain only a single command). | |
cce855bc | 4676 | |
f73dda09 JA |
4677 | @item POSIXLY_CORRECT |
4678 | If this variable is in the environment when @code{bash} starts, the shell | |
4679 | enters @sc{posix} mode (@pxref{Bash POSIX Mode}) before reading the | |
4680 | startup files, as if the @option{--posix} invocation option had been supplied. | |
4681 | If it is set while the shell is running, @code{bash} enables @sc{posix} mode, | |
4682 | as if the command | |
4683 | @example | |
4684 | @code{set -o posix} | |
4685 | @end example | |
4686 | @noindent | |
4687 | had been executed. | |
4688 | ||
bb70624e JA |
4689 | @item PPID |
4690 | The process @sc{id} of the shell's parent process. This variable | |
4691 | is readonly. | |
ccc6cda3 | 4692 | |
bb70624e JA |
4693 | @item PROMPT_COMMAND |
4694 | If set, the value is interpreted as a command to execute | |
28ef6c31 | 4695 | before the printing of each primary prompt (@env{$PS1}). |
ccc6cda3 | 4696 | |
bb70624e JA |
4697 | @item PS3 |
4698 | The value of this variable is used as the prompt for the | |
4699 | @code{select} command. If this variable is not set, the | |
4700 | @code{select} command prompts with @samp{#? } | |
ccc6cda3 | 4701 | |
bb70624e JA |
4702 | @item PS4 |
4703 | The value is the prompt printed before the command line is echoed | |
28ef6c31 JA |
4704 | when the @option{-x} option is set (@pxref{The Set Builtin}). |
4705 | The first character of @env{PS4} is replicated multiple times, as | |
bb70624e JA |
4706 | necessary, to indicate multiple levels of indirection. |
4707 | The default is @samp{+ }. | |
ccc6cda3 | 4708 | |
bb70624e JA |
4709 | @item PWD |
4710 | The current working directory as set by the @code{cd} builtin. | |
ccc6cda3 | 4711 | |
bb70624e JA |
4712 | @item RANDOM |
4713 | Each time this parameter is referenced, a random integer | |
4714 | between 0 and 32767 is generated. Assigning a value to this | |
4715 | variable seeds the random number generator. | |
ccc6cda3 | 4716 | |
bb70624e JA |
4717 | @item REPLY |
4718 | The default variable for the @code{read} builtin. | |
ccc6cda3 | 4719 | |
bb70624e JA |
4720 | @item SECONDS |
4721 | This variable expands to the number of seconds since the | |
4722 | shell was started. Assignment to this variable resets | |
4723 | the count to the value assigned, and the expanded value | |
4724 | becomes the value assigned plus the number of seconds | |
4725 | since the assignment. | |
ccc6cda3 | 4726 | |
b80f6443 JA |
4727 | @item SHELL |
4728 | The full pathname to the shell is kept in this environment variable. | |
4729 | If it is not set when the shell starts, | |
4730 | Bash assigns to it the full pathname of the current user's login shell. | |
4731 | ||
bb70624e JA |
4732 | @item SHELLOPTS |
4733 | A colon-separated list of enabled shell options. Each word in | |
28ef6c31 | 4734 | the list is a valid argument for the @option{-o} option to the |
bb70624e | 4735 | @code{set} builtin command (@pxref{The Set Builtin}). |
28ef6c31 | 4736 | The options appearing in @env{SHELLOPTS} are those reported |
bb70624e JA |
4737 | as @samp{on} by @samp{set -o}. |
4738 | If this variable is in the environment when Bash | |
4739 | starts up, each shell option in the list will be enabled before | |
4740 | reading any startup files. This variable is readonly. | |
ccc6cda3 | 4741 | |
bb70624e JA |
4742 | @item SHLVL |
4743 | Incremented by one each time a new instance of Bash is started. This is | |
4744 | intended to be a count of how deeply your Bash shells are nested. | |
ccc6cda3 | 4745 | |
bb70624e JA |
4746 | @item TIMEFORMAT |
4747 | The value of this parameter is used as a format string specifying | |
4748 | how the timing information for pipelines prefixed with the @code{time} | |
4749 | reserved word should be displayed. | |
4750 | The @samp{%} character introduces an | |
4751 | escape sequence that is expanded to a time value or other | |
4752 | information. | |
4753 | The escape sequences and their meanings are as | |
4754 | follows; the braces denote optional portions. | |
ccc6cda3 | 4755 | |
bb70624e | 4756 | @table @code |
ccc6cda3 | 4757 | |
bb70624e JA |
4758 | @item %% |
4759 | A literal @samp{%}. | |
ccc6cda3 | 4760 | |
bb70624e JA |
4761 | @item %[@var{p}][l]R |
4762 | The elapsed time in seconds. | |
ccc6cda3 | 4763 | |
bb70624e JA |
4764 | @item %[@var{p}][l]U |
4765 | The number of CPU seconds spent in user mode. | |
ccc6cda3 | 4766 | |
bb70624e JA |
4767 | @item %[@var{p}][l]S |
4768 | The number of CPU seconds spent in system mode. | |
ccc6cda3 | 4769 | |
bb70624e JA |
4770 | @item %P |
4771 | The CPU percentage, computed as (%U + %S) / %R. | |
4772 | @end table | |
ccc6cda3 | 4773 | |
bb70624e JA |
4774 | The optional @var{p} is a digit specifying the precision, the number of |
4775 | fractional digits after a decimal point. | |
4776 | A value of 0 causes no decimal point or fraction to be output. | |
4777 | At most three places after the decimal point may be specified; values | |
4778 | of @var{p} greater than 3 are changed to 3. | |
4779 | If @var{p} is not specified, the value 3 is used. | |
ccc6cda3 | 4780 | |
bb70624e JA |
4781 | The optional @code{l} specifies a longer format, including minutes, of |
4782 | the form @var{MM}m@var{SS}.@var{FF}s. | |
4783 | The value of @var{p} determines whether or not the fraction is included. | |
ccc6cda3 | 4784 | |
bb70624e JA |
4785 | If this variable is not set, Bash acts as if it had the value |
4786 | @example | |
4787 | @code{$'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS'} | |
4788 | @end example | |
4789 | If the value is null, no timing information is displayed. | |
4790 | A trailing newline is added when the format string is displayed. | |
ccc6cda3 | 4791 | |
bb70624e | 4792 | @item TMOUT |
7117c2d2 JA |
4793 | If set to a value greater than zero, @code{TMOUT} is treated as the |
4794 | default timeout for the @code{read} builtin (@pxref{Bash Builtins}). | |
4795 | The @code{select} command (@pxref{Conditional Constructs}) terminates | |
4796 | if input does not arrive after @code{TMOUT} seconds when input is coming | |
4797 | from a terminal. | |
4798 | ||
4799 | In an interative shell, the value is interpreted as | |
bb70624e JA |
4800 | the number of seconds to wait for input after issuing the primary |
4801 | prompt when the shell is interactive. | |
4802 | Bash terminates after that number of seconds if input does | |
4803 | not arrive. | |
ccc6cda3 | 4804 | |
95732b49 JA |
4805 | @item TMPDIR |
4806 | If set, Bash uses its value as the name of a directory in which | |
4807 | Bash creates temporary files for the shell's use. | |
4808 | ||
bb70624e JA |
4809 | @item UID |
4810 | The numeric real user id of the current user. This variable is readonly. | |
ccc6cda3 | 4811 | |
bb70624e | 4812 | @end vtable |
ccc6cda3 | 4813 | |
bb70624e JA |
4814 | @node Bash Features |
4815 | @chapter Bash Features | |
ccc6cda3 | 4816 | |
bb70624e | 4817 | This section describes features unique to Bash. |
ccc6cda3 | 4818 | |
bb70624e JA |
4819 | @menu |
4820 | * Invoking Bash:: Command line options that you can give | |
4821 | to Bash. | |
4822 | * Bash Startup Files:: When and how Bash executes scripts. | |
4823 | * Interactive Shells:: What an interactive shell is. | |
4824 | * Bash Conditional Expressions:: Primitives used in composing expressions for | |
4825 | the @code{test} builtin. | |
4826 | * Shell Arithmetic:: Arithmetic on shell variables. | |
4827 | * Aliases:: Substituting one command for another. | |
4828 | * Arrays:: Array Variables. | |
4829 | * The Directory Stack:: History of visited directories. | |
4830 | * Printing a Prompt:: Controlling the PS1 string. | |
4831 | * The Restricted Shell:: A more controlled mode of shell execution. | |
4832 | * Bash POSIX Mode:: Making Bash behave more closely to what | |
4833 | the POSIX standard specifies. | |
4834 | @end menu | |
ccc6cda3 | 4835 | |
bb70624e JA |
4836 | @node Invoking Bash |
4837 | @section Invoking Bash | |
ccc6cda3 | 4838 | |
bb70624e | 4839 | @example |
f73dda09 JA |
4840 | bash [long-opt] [-ir] [-abefhkmnptuvxdBCDHP] [-o @var{option}] [-O @var{shopt_option}] [@var{argument} @dots{}] |
4841 | bash [long-opt] [-abefhkmnptuvxdBCDHP] [-o @var{option}] [-O @var{shopt_option}] -c @var{string} [@var{argument} @dots{}] | |
4842 | bash [long-opt] -s [-abefhkmnptuvxdBCDHP] [-o @var{option}] [-O @var{shopt_option}] [@var{argument} @dots{}] | |
bb70624e | 4843 | @end example |
ccc6cda3 | 4844 | |
bb70624e JA |
4845 | In addition to the single-character shell command-line options |
4846 | (@pxref{The Set Builtin}), there are several multi-character | |
4847 | options that you can use. These options must appear on the command | |
7117c2d2 | 4848 | line before the single-character options to be recognized. |
ccc6cda3 | 4849 | |
bb70624e | 4850 | @table @code |
b80f6443 JA |
4851 | @item --debugger |
4852 | Arrange for the debugger profile to be executed before the shell | |
4853 | starts. Turns on extended debugging mode (see @ref{Bash Builtins} | |
4854 | for a description of the @code{extdebug} option to the @code{shopt} | |
4855 | builtin) and shell function tracing | |
4856 | (see @ref{The Set Builtin} for a description of the @code{-o functrace} | |
4857 | option). | |
4858 | ||
bb70624e JA |
4859 | @item --dump-po-strings |
4860 | A list of all double-quoted strings preceded by @samp{$} | |
95732b49 | 4861 | is printed on the standard output |
bb70624e | 4862 | in the @sc{gnu} @code{gettext} PO (portable object) file format. |
28ef6c31 | 4863 | Equivalent to @option{-D} except for the output format. |
ccc6cda3 | 4864 | |
bb70624e | 4865 | @item --dump-strings |
28ef6c31 | 4866 | Equivalent to @option{-D}. |
ccc6cda3 | 4867 | |
bb70624e JA |
4868 | @item --help |
4869 | Display a usage message on standard output and exit sucessfully. | |
ccc6cda3 | 4870 | |
28ef6c31 JA |
4871 | @item --init-file @var{filename} |
4872 | @itemx --rcfile @var{filename} | |
4873 | Execute commands from @var{filename} (instead of @file{~/.bashrc}) | |
4874 | in an interactive shell. | |
4875 | ||
bb70624e | 4876 | @item --login |
7117c2d2 | 4877 | Equivalent to @option{-l}. |
ccc6cda3 | 4878 | |
bb70624e JA |
4879 | @item --noediting |
4880 | Do not use the @sc{gnu} Readline library (@pxref{Command Line Editing}) | |
4881 | to read command lines when the shell is interactive. | |
ccc6cda3 | 4882 | |
bb70624e JA |
4883 | @item --noprofile |
4884 | Don't load the system-wide startup file @file{/etc/profile} | |
4885 | or any of the personal initialization files | |
4886 | @file{~/.bash_profile}, @file{~/.bash_login}, or @file{~/.profile} | |
4887 | when Bash is invoked as a login shell. | |
ccc6cda3 | 4888 | |
bb70624e JA |
4889 | @item --norc |
4890 | Don't read the @file{~/.bashrc} initialization file in an | |
4891 | interactive shell. This is on by default if the shell is | |
4892 | invoked as @code{sh}. | |
ccc6cda3 | 4893 | |
bb70624e JA |
4894 | @item --posix |
4895 | Change the behavior of Bash where the default operation differs | |
0628567a | 4896 | from the @sc{posix} standard to match the standard. This |
bb70624e JA |
4897 | is intended to make Bash behave as a strict superset of that |
4898 | standard. @xref{Bash POSIX Mode}, for a description of the Bash | |
4899 | @sc{posix} mode. | |
ccc6cda3 | 4900 | |
bb70624e JA |
4901 | @item --restricted |
4902 | Make the shell a restricted shell (@pxref{The Restricted Shell}). | |
ccc6cda3 | 4903 | |
bb70624e | 4904 | @item --verbose |
28ef6c31 | 4905 | Equivalent to @option{-v}. Print shell input lines as they're read. |
ccc6cda3 | 4906 | |
bb70624e JA |
4907 | @item --version |
4908 | Show version information for this instance of | |
4909 | Bash on the standard output and exit successfully. | |
ccc6cda3 | 4910 | |
ccc6cda3 JA |
4911 | @end table |
4912 | ||
bb70624e JA |
4913 | There are several single-character options that may be supplied at |
4914 | invocation which are not available with the @code{set} builtin. | |
cce855bc | 4915 | |
bb70624e JA |
4916 | @table @code |
4917 | @item -c @var{string} | |
4918 | Read and execute commands from @var{string} after processing the | |
4919 | options, then exit. Any remaining arguments are assigned to the | |
4920 | positional parameters, starting with @code{$0}. | |
ccc6cda3 | 4921 | |
bb70624e JA |
4922 | @item -i |
4923 | Force the shell to run interactively. Interactive shells are | |
4924 | described in @ref{Interactive Shells}. | |
ccc6cda3 | 4925 | |
7117c2d2 JA |
4926 | @item -l |
4927 | Make this shell act as if it had been directly invoked by login. | |
4928 | When the shell is interactive, this is equivalent to starting a | |
4929 | login shell with @samp{exec -l bash}. | |
4930 | When the shell is not interactive, the login shell startup files will | |
4931 | be executed. | |
4932 | @samp{exec bash -l} or @samp{exec bash --login} | |
4933 | will replace the current shell with a Bash login shell. | |
4934 | @xref{Bash Startup Files}, for a description of the special behavior | |
4935 | of a login shell. | |
4936 | ||
bb70624e JA |
4937 | @item -r |
4938 | Make the shell a restricted shell (@pxref{The Restricted Shell}). | |
ccc6cda3 | 4939 | |
bb70624e JA |
4940 | @item -s |
4941 | If this option is present, or if no arguments remain after option | |
4942 | processing, then commands are read from the standard input. | |
4943 | This option allows the positional parameters to be set | |
4944 | when invoking an interactive shell. | |
4945 | ||
4946 | @item -D | |
4947 | A list of all double-quoted strings preceded by @samp{$} | |
95732b49 | 4948 | is printed on the standard output. |
bb70624e JA |
4949 | These are the strings that |
4950 | are subject to language translation when the current locale | |
4951 | is not @code{C} or @code{POSIX} (@pxref{Locale Translation}). | |
28ef6c31 | 4952 | This implies the @option{-n} option; no commands will be executed. |
bb70624e | 4953 | |
f73dda09 JA |
4954 | @item [-+]O [@var{shopt_option}] |
4955 | @var{shopt_option} is one of the shell options accepted by the | |
4956 | @code{shopt} builtin (@pxref{Shell Builtin Commands}). | |
4957 | If @var{shopt_option} is present, @option{-O} sets the value of that option; | |
4958 | @option{+O} unsets it. | |
4959 | If @var{shopt_option} is not supplied, the names and values of the shell | |
4960 | options accepted by @code{shopt} are printed on the standard output. | |
4961 | If the invocation option is @option{+O}, the output is displayed in a format | |
4962 | that may be reused as input. | |
4963 | ||
bb70624e JA |
4964 | @item -- |
4965 | A @code{--} signals the end of options and disables further option | |
4966 | processing. | |
4967 | Any arguments after the @code{--} are treated as filenames and arguments. | |
4968 | ||
4969 | @end table | |
4970 | ||
f73dda09 JA |
4971 | @cindex login shell |
4972 | A @emph{login} shell is one whose first character of argument zero is | |
4973 | @samp{-}, or one invoked with the @option{--login} option. | |
4974 | ||
bb70624e JA |
4975 | @cindex interactive shell |
4976 | An @emph{interactive} shell is one started without non-option arguments, | |
28ef6c31 JA |
4977 | unless @option{-s} is specified, |
4978 | without specifying the @option{-c} option, and whose input and output are both | |
bb70624e | 4979 | connected to terminals (as determined by @code{isatty(3)}), or one |
28ef6c31 | 4980 | started with the @option{-i} option. @xref{Interactive Shells}, for more |
bb70624e JA |
4981 | information. |
4982 | ||
4983 | If arguments remain after option processing, and neither the | |
28ef6c31 | 4984 | @option{-c} nor the @option{-s} |
bb70624e JA |
4985 | option has been supplied, the first argument is assumed to |
4986 | be the name of a file containing shell commands (@pxref{Shell Scripts}). | |
4987 | When Bash is invoked in this fashion, @code{$0} | |
4988 | is set to the name of the file, and the positional parameters | |
4989 | are set to the remaining arguments. | |
4990 | Bash reads and executes commands from this file, then exits. | |
4991 | Bash's exit status is the exit status of the last command executed | |
4992 | in the script. If no commands are executed, the exit status is 0. | |
4993 | ||
4994 | @node Bash Startup Files | |
4995 | @section Bash Startup Files | |
4996 | @cindex startup files | |
4997 | ||
4998 | This section describs how Bash executes its startup files. | |
4999 | If any of the files exist but cannot be read, Bash reports an error. | |
5000 | Tildes are expanded in file names as described above under | |
5001 | Tilde Expansion (@pxref{Tilde Expansion}). | |
5002 | ||
5003 | Interactive shells are described in @ref{Interactive Shells}. | |
5004 | ||
28ef6c31 | 5005 | @subsubheading Invoked as an interactive login shell, or with @option{--login} |
bb70624e JA |
5006 | |
5007 | When Bash is invoked as an interactive login shell, or as a | |
28ef6c31 | 5008 | non-interactive shell with the @option{--login} option, it first reads and |
bb70624e JA |
5009 | executes commands from the file @file{/etc/profile}, if that file exists. |
5010 | After reading that file, it looks for @file{~/.bash_profile}, | |
5011 | @file{~/.bash_login}, and @file{~/.profile}, in that order, and reads | |
5012 | and executes commands from the first one that exists and is readable. | |
28ef6c31 | 5013 | The @option{--noprofile} option may be used when the shell is started to |
bb70624e JA |
5014 | inhibit this behavior. |
5015 | ||
5016 | When a login shell exits, Bash reads and executes commands from | |
5017 | the file @file{~/.bash_logout}, if it exists. | |
5018 | ||
5019 | @subsubheading Invoked as an interactive non-login shell | |
5020 | ||
5021 | When an interactive shell that is not a login shell is started, Bash | |
5022 | reads and executes commands from @file{~/.bashrc}, if that file exists. | |
28ef6c31 JA |
5023 | This may be inhibited by using the @option{--norc} option. |
5024 | The @option{--rcfile @var{file}} option will force Bash to read and | |
bb70624e JA |
5025 | execute commands from @var{file} instead of @file{~/.bashrc}. |
5026 | ||
5027 | So, typically, your @file{~/.bash_profile} contains the line | |
5028 | @example | |
5029 | @code{if [ -f ~/.bashrc ]; then . ~/.bashrc; fi} | |
5030 | @end example | |
5031 | @noindent | |
5032 | after (or before) any login-specific initializations. | |
5033 | ||
5034 | @subsubheading Invoked non-interactively | |
5035 | ||
5036 | When Bash is started non-interactively, to run a shell script, | |
28ef6c31 | 5037 | for example, it looks for the variable @env{BASH_ENV} in the environment, |
bb70624e JA |
5038 | expands its value if it appears there, and uses the expanded value as |
5039 | the name of a file to read and execute. Bash behaves as if the | |
5040 | following command were executed: | |
5041 | @example | |
5042 | @code{if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi} | |
5043 | @end example | |
5044 | @noindent | |
28ef6c31 | 5045 | but the value of the @env{PATH} variable is not used to search for the |
bb70624e JA |
5046 | file name. |
5047 | ||
28ef6c31 JA |
5048 | As noted above, if a non-interactive shell is invoked with the |
5049 | @option{--login} option, Bash attempts to read and execute commands from the | |
5050 | login shell startup files. | |
5051 | ||
bb70624e JA |
5052 | @subsubheading Invoked with name @code{sh} |
5053 | ||
5054 | If Bash is invoked with the name @code{sh}, it tries to mimic the | |
5055 | startup behavior of historical versions of @code{sh} as closely as | |
5056 | possible, while conforming to the @sc{posix} standard as well. | |
5057 | ||
5058 | When invoked as an interactive login shell, or as a non-interactive | |
28ef6c31 | 5059 | shell with the @option{--login} option, it first attempts to read |
bb70624e JA |
5060 | and execute commands from @file{/etc/profile} and @file{~/.profile}, in |
5061 | that order. | |
28ef6c31 | 5062 | The @option{--noprofile} option may be used to inhibit this behavior. |
bb70624e | 5063 | When invoked as an interactive shell with the name @code{sh}, Bash |
28ef6c31 | 5064 | looks for the variable @env{ENV}, expands its value if it is defined, |
bb70624e JA |
5065 | and uses the expanded value as the name of a file to read and execute. |
5066 | Since a shell invoked as @code{sh} does not attempt to read and execute | |
28ef6c31 | 5067 | commands from any other startup files, the @option{--rcfile} option has |
bb70624e JA |
5068 | no effect. |
5069 | A non-interactive shell invoked with the name @code{sh} does not attempt | |
5070 | to read any other startup files. | |
5071 | ||
5072 | When invoked as @code{sh}, Bash enters @sc{posix} mode after | |
5073 | the startup files are read. | |
5074 | ||
5075 | @subsubheading Invoked in @sc{posix} mode | |
5076 | ||
5077 | When Bash is started in @sc{posix} mode, as with the | |
28ef6c31 | 5078 | @option{--posix} command line option, it follows the @sc{posix} standard |
bb70624e | 5079 | for startup files. |
28ef6c31 | 5080 | In this mode, interactive shells expand the @env{ENV} variable |
bb70624e JA |
5081 | and commands are read and executed from the file whose name is the |
5082 | expanded value. | |
5083 | No other startup files are read. | |
5084 | ||
5085 | @subsubheading Invoked by remote shell daemon | |
5086 | ||
5087 | Bash attempts to determine when it is being run by the remote shell | |
5088 | daemon, usually @code{rshd}. If Bash determines it is being run by | |
5089 | rshd, it reads and executes commands from @file{~/.bashrc}, if that | |
5090 | file exists and is readable. | |
5091 | It will not do this if invoked as @code{sh}. | |
28ef6c31 JA |
5092 | The @option{--norc} option may be used to inhibit this behavior, and the |
5093 | @option{--rcfile} option may be used to force another file to be read, but | |
bb70624e JA |
5094 | @code{rshd} does not generally invoke the shell with those options or |
5095 | allow them to be specified. | |
5096 | ||
5097 | @subsubheading Invoked with unequal effective and real @sc{uid/gid}s | |
5098 | ||
5099 | If Bash is started with the effective user (group) id not equal to the | |
5100 | real user (group) id, and the @code{-p} option is not supplied, no startup | |
5101 | files are read, shell functions are not inherited from the environment, | |
28ef6c31 | 5102 | the @env{SHELLOPTS} variable, if it appears in the environment, is ignored, |
bb70624e JA |
5103 | and the effective user id is set to the real user id. |
5104 | If the @code{-p} option is supplied at invocation, the startup behavior is | |
5105 | the same, but the effective user id is not reset. | |
5106 | ||
5107 | @node Interactive Shells | |
5108 | @section Interactive Shells | |
5109 | @cindex interactive shell | |
5110 | @cindex shell, interactive | |
5111 | ||
5112 | @menu | |
5113 | * What is an Interactive Shell?:: What determines whether a shell is Interactive. | |
5114 | * Is this Shell Interactive?:: How to tell if a shell is interactive. | |
5115 | * Interactive Shell Behavior:: What changes in a interactive shell? | |
5116 | @end menu | |
5117 | ||
5118 | @node What is an Interactive Shell? | |
5119 | @subsection What is an Interactive Shell? | |
5120 | ||
5121 | An interactive shell | |
28ef6c31 JA |
5122 | is one started without non-option arguments, unless @option{-s} is |
5123 | specified, without specifiying the @option{-c} option, and | |
b80f6443 | 5124 | whose input and error output are both |
bb70624e | 5125 | connected to terminals (as determined by @code{isatty(3)}), |
28ef6c31 | 5126 | or one started with the @option{-i} option. |
bb70624e JA |
5127 | |
5128 | An interactive shell generally reads from and writes to a user's | |
5129 | terminal. | |
5130 | ||
28ef6c31 | 5131 | The @option{-s} invocation option may be used to set the positional parameters |
bb70624e JA |
5132 | when an interactive shell is started. |
5133 | ||
5134 | @node Is this Shell Interactive? | |
5135 | @subsection Is this Shell Interactive? | |
5136 | ||
5137 | To determine within a startup script whether or not Bash is | |
5138 | running interactively, | |
5139 | test the value of the @samp{-} special parameter. | |
5140 | It contains @code{i} when the shell is interactive. For example: | |
5141 | ||
5142 | @example | |
5143 | case "$-" in | |
5144 | *i*) echo This shell is interactive ;; | |
5145 | *) echo This shell is not interactive ;; | |
5146 | esac | |
5147 | @end example | |
5148 | ||
5149 | Alternatively, startup scripts may examine the variable | |
28ef6c31 | 5150 | @env{PS1}; it is unset in non-interactive shells, and set in |
bb70624e JA |
5151 | interactive shells. Thus: |
5152 | ||
5153 | @example | |
5154 | if [ -z "$PS1" ]; then | |
5155 | echo This shell is not interactive | |
5156 | else | |
5157 | echo This shell is interactive | |
5158 | fi | |
5159 | @end example | |
5160 | ||
5161 | @node Interactive Shell Behavior | |
5162 | @subsection Interactive Shell Behavior | |
5163 | ||
5164 | When the shell is running interactively, it changes its behavior in | |
5165 | several ways. | |
5166 | ||
5167 | @enumerate | |
5168 | @item | |
5169 | Startup files are read and executed as described in @ref{Bash Startup Files}. | |
5170 | ||
5171 | @item | |
5172 | Job Control (@pxref{Job Control}) is enabled by default. When job | |
5173 | control is in effect, Bash ignores the keyboard-generated job control | |
5174 | signals @code{SIGTTIN}, @code{SIGTTOU}, and @code{SIGTSTP}. | |
5175 | ||
5176 | @item | |
28ef6c31 JA |
5177 | Bash expands and displays @env{PS1} before reading the first line |
5178 | of a command, and expands and displays @env{PS2} before reading the | |
bb70624e JA |
5179 | second and subsequent lines of a multi-line command. |
5180 | ||
5181 | @item | |
28ef6c31 JA |
5182 | Bash executes the value of the @env{PROMPT_COMMAND} variable as a command |
5183 | before printing the primary prompt, @env{$PS1} | |
bb70624e JA |
5184 | (@pxref{Bash Variables}). |
5185 | ||
5186 | @item | |
5187 | Readline (@pxref{Command Line Editing}) is used to read commands from | |
5188 | the user's terminal. | |
5189 | ||
5190 | @item | |
5191 | Bash inspects the value of the @code{ignoreeof} option to @code{set -o} | |
5192 | instead of exiting immediately when it receives an @code{EOF} on its | |
5193 | standard input when reading a command (@pxref{The Set Builtin}). | |
5194 | ||
5195 | @item | |
5196 | Command history (@pxref{Bash History Facilities}) | |
5197 | and history expansion (@pxref{History Interaction}) | |
5198 | are enabled by default. | |
28ef6c31 | 5199 | Bash will save the command history to the file named by @env{$HISTFILE} |
bb70624e JA |
5200 | when an interactive shell exits. |
5201 | ||
5202 | @item | |
5203 | Alias expansion (@pxref{Aliases}) is performed by default. | |
5204 | ||
5205 | @item | |
5206 | In the absence of any traps, Bash ignores @code{SIGTERM} | |
5207 | (@pxref{Signals}). | |
5208 | ||
5209 | @item | |
5210 | In the absence of any traps, @code{SIGINT} is caught and handled | |
5211 | ((@pxref{Signals}). | |
5212 | @code{SIGINT} will interrupt some shell builtins. | |
5213 | ||
5214 | @item | |
5215 | An interactive login shell sends a @code{SIGHUP} to all jobs on exit | |
5216 | if the @code{hupoxexit} shell option has been enabled (@pxref{Signals}). | |
5217 | ||
5218 | @item | |
28ef6c31 | 5219 | The @option{-n} invocation option is ignored, and @samp{set -n} has |
bb70624e JA |
5220 | no effect (@pxref{The Set Builtin}). |
5221 | ||
5222 | @item | |
5223 | Bash will check for mail periodically, depending on the values of the | |
28ef6c31 | 5224 | @env{MAIL}, @env{MAILPATH}, and @env{MAILCHECK} shell variables |
bb70624e JA |
5225 | (@pxref{Bash Variables}). |
5226 | ||
5227 | @item | |
5228 | Expansion errors due to references to unbound shell variables after | |
5229 | @samp{set -u} has been enabled will not cause the shell to exit | |
5230 | (@pxref{The Set Builtin}). | |
5231 | ||
5232 | @item | |
5233 | The shell will not exit on expansion errors caused by @var{var} being unset | |
5234 | or null in @code{$@{@var{var}:?@var{word}@}} expansions | |
5235 | (@pxref{Shell Parameter Expansion}). | |
5236 | ||
5237 | @item | |
5238 | Redirection errors encountered by shell builtins will not cause the | |
5239 | shell to exit. | |
5240 | ||
5241 | @item | |
5242 | When running in @sc{posix} mode, a special builtin returning an error | |
5243 | status will not cause the shell to exit (@pxref{Bash POSIX Mode}). | |
95732b49 | 5244 | |
bb70624e JA |
5245 | @item |
5246 | A failed @code{exec} will not cause the shell to exit | |
5247 | (@pxref{Bourne Shell Builtins}). | |
5248 | ||
5249 | @item | |
5250 | Parser syntax errors will not cause the shell to exit. | |
5251 | ||
5252 | @item | |
5253 | Simple spelling correction for directory arguments to the @code{cd} | |
5254 | builtin is enabled by default (see the description of the @code{cdspell} | |
5255 | option to the @code{shopt} builtin in @ref{Bash Builtins}). | |
5256 | ||
5257 | @item | |
28ef6c31 | 5258 | The shell will check the value of the @env{TMOUT} variable and exit |
bb70624e | 5259 | if a command is not read within the specified number of seconds after |
28ef6c31 | 5260 | printing @env{$PS1} (@pxref{Bash Variables}). |
bb70624e JA |
5261 | |
5262 | @end enumerate | |
5263 | ||
5264 | @node Bash Conditional Expressions | |
5265 | @section Bash Conditional Expressions | |
5266 | @cindex expressions, conditional | |
5267 | ||
5268 | Conditional expressions are used by the @code{[[} compound command | |
5269 | and the @code{test} and @code{[} builtin commands. | |
5270 | ||
5271 | Expressions may be unary or binary. | |
5272 | Unary expressions are often used to examine the status of a file. | |
5273 | There are string operators and numeric comparison operators as well. | |
5274 | If the @var{file} argument to one of the primaries is of the form | |
5275 | @file{/dev/fd/@var{N}}, then file descriptor @var{N} is checked. | |
5276 | If the @var{file} argument to one of the primaries is one of | |
5277 | @file{/dev/stdin}, @file{/dev/stdout}, or @file{/dev/stderr}, file | |
5278 | descriptor 0, 1, or 2, respectively, is checked. | |
ccc6cda3 | 5279 | |
95732b49 JA |
5280 | Unless otherwise specified, primaries that operate on files follow symbolic |
5281 | links and operate on the target of the link, rather than the link itself. | |
5282 | ||
ccc6cda3 | 5283 | @table @code |
cce855bc JA |
5284 | @item -a @var{file} |
5285 | True if @var{file} exists. | |
5286 | ||
ccc6cda3 JA |
5287 | @item -b @var{file} |
5288 | True if @var{file} exists and is a block special file. | |
5289 | ||
5290 | @item -c @var{file} | |
5291 | True if @var{file} exists and is a character special file. | |
5292 | ||
5293 | @item -d @var{file} | |
5294 | True if @var{file} exists and is a directory. | |
5295 | ||
5296 | @item -e @var{file} | |
5297 | True if @var{file} exists. | |
5298 | ||
5299 | @item -f @var{file} | |
5300 | True if @var{file} exists and is a regular file. | |
5301 | ||
5302 | @item -g @var{file} | |
cce855bc | 5303 | True if @var{file} exists and its set-group-id bit is set. |
ccc6cda3 | 5304 | |
b72432fd JA |
5305 | @item -h @var{file} |
5306 | True if @var{file} exists and is a symbolic link. | |
5307 | ||
ccc6cda3 | 5308 | @item -k @var{file} |
cce855bc | 5309 | True if @var{file} exists and its "sticky" bit is set. |
ccc6cda3 JA |
5310 | |
5311 | @item -p @var{file} | |
cce855bc | 5312 | True if @var{file} exists and is a named pipe (FIFO). |
ccc6cda3 JA |
5313 | |
5314 | @item -r @var{file} | |
5315 | True if @var{file} exists and is readable. | |
5316 | ||
5317 | @item -s @var{file} | |
5318 | True if @var{file} exists and has a size greater than zero. | |
5319 | ||
ccc6cda3 | 5320 | @item -t @var{fd} |
cce855bc | 5321 | True if file descriptor @var{fd} is open and refers to a terminal. |
ccc6cda3 JA |
5322 | |
5323 | @item -u @var{file} | |
5324 | True if @var{file} exists and its set-user-id bit is set. | |
5325 | ||
5326 | @item -w @var{file} | |
5327 | True if @var{file} exists and is writable. | |
5328 | ||
5329 | @item -x @var{file} | |
5330 | True if @var{file} exists and is executable. | |
5331 | ||
5332 | @item -O @var{file} | |
5333 | True if @var{file} exists and is owned by the effective user id. | |
5334 | ||
5335 | @item -G @var{file} | |
5336 | True if @var{file} exists and is owned by the effective group id. | |
5337 | ||
cce855bc JA |
5338 | @item -L @var{file} |
5339 | True if @var{file} exists and is a symbolic link. | |
5340 | ||
5341 | @item -S @var{file} | |
5342 | True if @var{file} exists and is a socket. | |
5343 | ||
5344 | @item -N @var{file} | |
5345 | True if @var{file} exists and has been modified since it was last read. | |
5346 | ||
ccc6cda3 | 5347 | @item @var{file1} -nt @var{file2} |
7117c2d2 JA |
5348 | True if @var{file1} is newer (according to modification date) |
5349 | than @var{file2}, or if @var{file1} exists and @var{file2} does not. | |
ccc6cda3 JA |
5350 | |
5351 | @item @var{file1} -ot @var{file2} | |
7117c2d2 JA |
5352 | True if @var{file1} is older than @var{file2}, |
5353 | or if @var{file2} exists and @var{file1} does not. | |
ccc6cda3 JA |
5354 | |
5355 | @item @var{file1} -ef @var{file2} | |
7117c2d2 | 5356 | True if @var{file1} and @var{file2} refer to the same device and |
ccc6cda3 JA |
5357 | inode numbers. |
5358 | ||
5359 | @item -o @var{optname} | |
5360 | True if shell option @var{optname} is enabled. | |
28ef6c31 | 5361 | The list of options appears in the description of the @option{-o} |
ccc6cda3 JA |
5362 | option to the @code{set} builtin (@pxref{The Set Builtin}). |
5363 | ||
5364 | @item -z @var{string} | |
5365 | True if the length of @var{string} is zero. | |
5366 | ||
5367 | @item -n @var{string} | |
5368 | @itemx @var{string} | |
5369 | True if the length of @var{string} is non-zero. | |
5370 | ||
cce855bc JA |
5371 | @item @var{string1} == @var{string2} |
5372 | True if the strings are equal. | |
7117c2d2 | 5373 | @samp{=} may be used in place of @samp{==} for strict @sc{posix} compliance. |
ccc6cda3 JA |
5374 | |
5375 | @item @var{string1} != @var{string2} | |
5376 | True if the strings are not equal. | |
5377 | ||
5378 | @item @var{string1} < @var{string2} | |
cce855bc JA |
5379 | True if @var{string1} sorts before @var{string2} lexicographically |
5380 | in the current locale. | |
ccc6cda3 JA |
5381 | |
5382 | @item @var{string1} > @var{string2} | |
cce855bc JA |
5383 | True if @var{string1} sorts after @var{string2} lexicographically |
5384 | in the current locale. | |
ccc6cda3 JA |
5385 | |
5386 | @item @var{arg1} OP @var{arg2} | |
5387 | @code{OP} is one of | |
5388 | @samp{-eq}, @samp{-ne}, @samp{-lt}, @samp{-le}, @samp{-gt}, or @samp{-ge}. | |
5389 | These arithmetic binary operators return true if @var{arg1} | |
5390 | is equal to, not equal to, less than, less than or equal to, | |
5391 | greater than, or greater than or equal to @var{arg2}, | |
5392 | respectively. @var{Arg1} and @var{arg2} | |
5393 | may be positive or negative integers. | |
5394 | ||
5395 | @end table | |
5396 | ||
bb70624e JA |
5397 | @node Shell Arithmetic |
5398 | @section Shell Arithmetic | |
5399 | @cindex arithmetic, shell | |
5400 | @cindex shell arithmetic | |
5401 | @cindex expressions, arithmetic | |
5402 | @cindex evaluation, arithmetic | |
5403 | @cindex arithmetic evaluation | |
ccc6cda3 | 5404 | |
bb70624e | 5405 | The shell allows arithmetic expressions to be evaluated, as one of |
b80f6443 JA |
5406 | the shell expansions or by the @code{let} and the @option{-i} option |
5407 | to the @code{declare} builtins. | |
ccc6cda3 | 5408 | |
7117c2d2 | 5409 | Evaluation is done in fixed-width integers with no check for overflow, |
bb70624e | 5410 | though division by 0 is trapped and flagged as an error. |
b80f6443 JA |
5411 | The operators and their precedence, associativity, and values |
5412 | are the same as in the C language. | |
bb70624e JA |
5413 | The following list of operators is grouped into levels of |
5414 | equal-precedence operators. | |
5415 | The levels are listed in order of decreasing precedence. | |
cce855bc | 5416 | |
bb70624e | 5417 | @table @code |
d166f048 | 5418 | |
bb70624e JA |
5419 | @item @var{id}++ @var{id}-- |
5420 | variable post-increment and post-decrement | |
cce855bc | 5421 | |
bb70624e JA |
5422 | @item ++@var{id} --@var{id} |
5423 | variable pre-increment and pre-decrement | |
ccc6cda3 | 5424 | |
bb70624e JA |
5425 | @item - + |
5426 | unary minus and plus | |
ccc6cda3 | 5427 | |
bb70624e JA |
5428 | @item ! ~ |
5429 | logical and bitwise negation | |
ccc6cda3 | 5430 | |
bb70624e JA |
5431 | @item ** |
5432 | exponentiation | |
ccc6cda3 | 5433 | |
bb70624e JA |
5434 | @item * / % |
5435 | multiplication, division, remainder | |
ccc6cda3 | 5436 | |
bb70624e JA |
5437 | @item + - |
5438 | addition, subtraction | |
cce855bc | 5439 | |
bb70624e JA |
5440 | @item << >> |
5441 | left and right bitwise shifts | |
cce855bc | 5442 | |
bb70624e JA |
5443 | @item <= >= < > |
5444 | comparison | |
ccc6cda3 | 5445 | |
bb70624e JA |
5446 | @item == != |
5447 | equality and inequality | |
ccc6cda3 | 5448 | |
bb70624e JA |
5449 | @item & |
5450 | bitwise AND | |
ccc6cda3 | 5451 | |
bb70624e JA |
5452 | @item ^ |
5453 | bitwise exclusive OR | |
ccc6cda3 | 5454 | |
bb70624e JA |
5455 | @item | |
5456 | bitwise OR | |
cce855bc | 5457 | |
bb70624e JA |
5458 | @item && |
5459 | logical AND | |
cce855bc | 5460 | |
bb70624e JA |
5461 | @item || |
5462 | logical OR | |
cce855bc | 5463 | |
bb70624e | 5464 | @item expr ? expr : expr |
b80f6443 | 5465 | conditional operator |
cce855bc | 5466 | |
bb70624e JA |
5467 | @item = *= /= %= += -= <<= >>= &= ^= |= |
5468 | assignment | |
cce855bc | 5469 | |
bb70624e JA |
5470 | @item expr1 , expr2 |
5471 | comma | |
5472 | @end table | |
ccc6cda3 | 5473 | |
bb70624e JA |
5474 | Shell variables are allowed as operands; parameter expansion is |
5475 | performed before the expression is evaluated. | |
5476 | Within an expression, shell variables may also be referenced by name | |
5477 | without using the parameter expansion syntax. | |
b80f6443 JA |
5478 | A shell variable that is null or unset evaluates to 0 when referenced |
5479 | by name without using the parameter expansion syntax. | |
bb70624e | 5480 | The value of a variable is evaluated as an arithmetic expression |
b80f6443 JA |
5481 | when it is referenced, or when a variable which has been given the |
5482 | @var{integer} attribute using @samp{declare -i} is assigned a value. | |
5483 | A null value evaluates to 0. | |
bb70624e JA |
5484 | A shell variable need not have its integer attribute turned on |
5485 | to be used in an expression. | |
ccc6cda3 | 5486 | |
bb70624e JA |
5487 | Constants with a leading 0 are interpreted as octal numbers. |
5488 | A leading @samp{0x} or @samp{0X} denotes hexadecimal. Otherwise, | |
5489 | numbers take the form [@var{base}@code{#}]@var{n}, where @var{base} | |
5490 | is a decimal number between 2 and 64 representing the arithmetic | |
5491 | base, and @var{n} is a number in that base. If @var{base}@code{#} is | |
5492 | omitted, then base 10 is used. | |
5493 | The digits greater than 9 are represented by the lowercase letters, | |
f73dda09 | 5494 | the uppercase letters, @samp{@@}, and @samp{_}, in that order. |
bb70624e | 5495 | If @var{base} is less than or equal to 36, lowercase and uppercase |
95732b49 | 5496 | letters may be used interchangeably to represent numbers between 10 |
bb70624e | 5497 | and 35. |
ccc6cda3 | 5498 | |
bb70624e JA |
5499 | Operators are evaluated in order of precedence. Sub-expressions in |
5500 | parentheses are evaluated first and may override the precedence | |
5501 | rules above. | |
ccc6cda3 | 5502 | |
bb70624e JA |
5503 | @node Aliases |
5504 | @section Aliases | |
5505 | @cindex alias expansion | |
ccc6cda3 | 5506 | |
bb70624e JA |
5507 | @var{Aliases} allow a string to be substituted for a word when it is used |
5508 | as the first word of a simple command. | |
5509 | The shell maintains a list of aliases that may be set and unset with | |
5510 | the @code{alias} and @code{unalias} builtin commands. | |
ccc6cda3 | 5511 | |
bb70624e JA |
5512 | The first word of each simple command, if unquoted, is checked to see |
5513 | if it has an alias. | |
5514 | If so, that word is replaced by the text of the alias. | |
b80f6443 JA |
5515 | The characters @samp{/}, @samp{$}, @samp{`}, @samp{=} and any of the |
5516 | shell metacharacters or quoting characters listed above may not appear | |
5517 | in an alias name. | |
5518 | The replacement text may contain any valid | |
5519 | shell input, including shell metacharacters. | |
bb70624e JA |
5520 | The first word of the replacement text is tested for |
5521 | aliases, but a word that is identical to an alias being expanded | |
b80f6443 JA |
5522 | is not expanded a second time. |
5523 | This means that one may alias @code{ls} to @code{"ls -F"}, | |
bb70624e JA |
5524 | for instance, and Bash does not try to recursively expand the |
5525 | replacement text. If the last character of the alias value is a | |
5526 | space or tab character, then the next command word following the | |
5527 | alias is also checked for alias expansion. | |
ccc6cda3 | 5528 | |
bb70624e JA |
5529 | Aliases are created and listed with the @code{alias} |
5530 | command, and removed with the @code{unalias} command. | |
ccc6cda3 | 5531 | |
bb70624e JA |
5532 | There is no mechanism for using arguments in the replacement text, |
5533 | as in @code{csh}. | |
5534 | If arguments are needed, a shell function should be used | |
5535 | (@pxref{Shell Functions}). | |
ccc6cda3 | 5536 | |
bb70624e JA |
5537 | Aliases are not expanded when the shell is not interactive, |
5538 | unless the @code{expand_aliases} shell option is set using | |
5539 | @code{shopt} (@pxref{Bash Builtins}). | |
ccc6cda3 | 5540 | |
bb70624e JA |
5541 | The rules concerning the definition and use of aliases are |
5542 | somewhat confusing. Bash | |
5543 | always reads at least one complete line | |
5544 | of input before executing any | |
5545 | of the commands on that line. Aliases are expanded when a | |
5546 | command is read, not when it is executed. Therefore, an | |
5547 | alias definition appearing on the same line as another | |
5548 | command does not take effect until the next line of input is read. | |
5549 | The commands following the alias definition | |
5550 | on that line are not affected by the new alias. | |
5551 | This behavior is also an issue when functions are executed. | |
5552 | Aliases are expanded when a function definition is read, | |
5553 | not when the function is executed, because a function definition | |
5554 | is itself a compound command. As a consequence, aliases | |
5555 | defined in a function are not available until after that | |
5556 | function is executed. To be safe, always put | |
5557 | alias definitions on a separate line, and do not use @code{alias} | |
5558 | in compound commands. | |
ccc6cda3 | 5559 | |
bb70624e | 5560 | For almost every purpose, shell functions are preferred over aliases. |
ccc6cda3 | 5561 | |
bb70624e JA |
5562 | @node Arrays |
5563 | @section Arrays | |
5564 | @cindex arrays | |
d166f048 | 5565 | |
bb70624e JA |
5566 | Bash provides one-dimensional array variables. Any variable may be used as |
5567 | an array; the @code{declare} builtin will explicitly declare an array. | |
5568 | There is no maximum | |
5569 | limit on the size of an array, nor any requirement that members | |
5570 | be indexed or assigned contiguously. Arrays are zero-based. | |
ccc6cda3 | 5571 | |
bb70624e JA |
5572 | An array is created automatically if any variable is assigned to using |
5573 | the syntax | |
5574 | @example | |
5575 | name[@var{subscript}]=@var{value} | |
5576 | @end example | |
ccc6cda3 | 5577 | |
bb70624e JA |
5578 | @noindent |
5579 | The @var{subscript} | |
5580 | is treated as an arithmetic expression that must evaluate to a number | |
5581 | greater than or equal to zero. To explicitly declare an array, use | |
5582 | @example | |
5583 | declare -a @var{name} | |
5584 | @end example | |
5585 | @noindent | |
5586 | The syntax | |
5587 | @example | |
5588 | declare -a @var{name}[@var{subscript}] | |
5589 | @end example | |
5590 | @noindent | |
5591 | is also accepted; the @var{subscript} is ignored. Attributes may be | |
5592 | specified for an array variable using the @code{declare} and | |
5593 | @code{readonly} builtins. Each attribute applies to all members of | |
5594 | an array. | |
ccc6cda3 | 5595 | |
bb70624e JA |
5596 | Arrays are assigned to using compound assignments of the form |
5597 | @example | |
5598 | name=(value@var{1} @dots{} value@var{n}) | |
5599 | @end example | |
5600 | @noindent | |
5601 | where each | |
5602 | @var{value} is of the form @code{[[@var{subscript}]=]}@var{string}. If | |
5603 | the optional subscript is supplied, that index is assigned to; | |
5604 | otherwise the index of the element assigned is the last index assigned | |
5605 | to by the statement plus one. Indexing starts at zero. | |
5606 | This syntax is also accepted by the @code{declare} | |
5607 | builtin. Individual array elements may be assigned to using the | |
5608 | @code{name[}@var{subscript}@code{]=}@var{value} syntax introduced above. | |
cce855bc | 5609 | |
bb70624e JA |
5610 | Any element of an array may be referenced using |
5611 | @code{$@{name[}@var{subscript}@code{]@}}. | |
5612 | The braces are required to avoid | |
5613 | conflicts with the shell's filename expansion operators. If the | |
5614 | @var{subscript} is @samp{@@} or @samp{*}, the word expands to all members | |
5615 | of the array @var{name}. These subscripts differ only when the word | |
95732b49 JA |
5616 | appears within double quotes. |
5617 | If the word is double-quoted, | |
bb70624e JA |
5618 | @code{$@{name[*]@}} expands to a single word with |
5619 | the value of each array member separated by the first character of the | |
28ef6c31 | 5620 | @env{IFS} variable, and @code{$@{name[@@]@}} expands each element of |
bb70624e | 5621 | @var{name} to a separate word. When there are no array members, |
95732b49 JA |
5622 | @code{$@{name[@@]@}} expands to nothing. |
5623 | If the double-quoted expansion occurs within a word, the expansion of | |
5624 | the first parameter is joined with the beginning part of the original | |
5625 | word, and the expansion of the last parameter is joined with the last | |
5626 | part of the original word. | |
5627 | This is analogous to the | |
bb70624e JA |
5628 | expansion of the special parameters @samp{@@} and @samp{*}. |
5629 | @code{$@{#name[}@var{subscript}@code{]@}} expands to the length of | |
5630 | @code{$@{name[}@var{subscript}@code{]@}}. | |
5631 | If @var{subscript} is @samp{@@} or | |
5632 | @samp{*}, the expansion is the number of elements in the array. | |
5633 | Referencing an array variable without a subscript is equivalent to | |
5634 | referencing element zero. | |
ccc6cda3 | 5635 | |
bb70624e | 5636 | The @code{unset} builtin is used to destroy arrays. |
f73dda09 | 5637 | @code{unset} @var{name}[@var{subscript}] |
bb70624e | 5638 | destroys the array element at index @var{subscript}. |
95732b49 JA |
5639 | Care must be taken to avoid unwanted side effects caused by filename |
5640 | generation. | |
bb70624e JA |
5641 | @code{unset} @var{name}, where @var{name} is an array, removes the |
5642 | entire array. A subscript of @samp{*} or @samp{@@} also removes the | |
5643 | entire array. | |
ccc6cda3 | 5644 | |
bb70624e | 5645 | The @code{declare}, @code{local}, and @code{readonly} |
28ef6c31 | 5646 | builtins each accept a @option{-a} |
bb70624e | 5647 | option to specify an array. The @code{read} |
28ef6c31 | 5648 | builtin accepts a @option{-a} |
bb70624e JA |
5649 | option to assign a list of words read from the standard input |
5650 | to an array, and can read values from the standard input into | |
5651 | individual array elements. The @code{set} and @code{declare} | |
5652 | builtins display array values in a way that allows them to be | |
5653 | reused as input. | |
ccc6cda3 | 5654 | |
bb70624e JA |
5655 | @node The Directory Stack |
5656 | @section The Directory Stack | |
5657 | @cindex directory stack | |
ccc6cda3 | 5658 | |
bb70624e JA |
5659 | @menu |
5660 | * Directory Stack Builtins:: Bash builtin commands to manipulate | |
5661 | the directory stack. | |
5662 | @end menu | |
ccc6cda3 | 5663 | |
bb70624e JA |
5664 | The directory stack is a list of recently-visited directories. The |
5665 | @code{pushd} builtin adds directories to the stack as it changes | |
5666 | the current directory, and the @code{popd} builtin removes specified | |
5667 | directories from the stack and changes the current directory to | |
5668 | the directory removed. The @code{dirs} builtin displays the contents | |
5669 | of the directory stack. | |
ccc6cda3 | 5670 | |
bb70624e | 5671 | The contents of the directory stack are also visible |
28ef6c31 | 5672 | as the value of the @env{DIRSTACK} shell variable. |
ccc6cda3 | 5673 | |
bb70624e JA |
5674 | @node Directory Stack Builtins |
5675 | @subsection Directory Stack Builtins | |
ccc6cda3 | 5676 | |
bb70624e | 5677 | @table @code |
ccc6cda3 | 5678 | |
bb70624e JA |
5679 | @item dirs |
5680 | @btindex dirs | |
5681 | @example | |
5682 | dirs [+@var{N} | -@var{N}] [-clpv] | |
5683 | @end example | |
5684 | Display the list of currently remembered directories. Directories | |
5685 | are added to the list with the @code{pushd} command; the | |
5686 | @code{popd} command removes directories from the list. | |
5687 | @table @code | |
5688 | @item +@var{N} | |
5689 | Displays the @var{N}th directory (counting from the left of the | |
5690 | list printed by @code{dirs} when invoked without options), starting | |
5691 | with zero. | |
5692 | @item -@var{N} | |
5693 | Displays the @var{N}th directory (counting from the right of the | |
5694 | list printed by @code{dirs} when invoked without options), starting | |
5695 | with zero. | |
5696 | @item -c | |
5697 | Clears the directory stack by deleting all of the elements. | |
5698 | @item -l | |
5699 | Produces a longer listing; the default listing format uses a | |
5700 | tilde to denote the home directory. | |
5701 | @item -p | |
5702 | Causes @code{dirs} to print the directory stack with one entry per | |
5703 | line. | |
5704 | @item -v | |
5705 | Causes @code{dirs} to print the directory stack with one entry per | |
5706 | line, prefixing each entry with its index in the stack. | |
5707 | @end table | |
5708 | ||
5709 | @item popd | |
5710 | @btindex popd | |
5711 | @example | |
5712 | popd [+@var{N} | -@var{N}] [-n] | |
5713 | @end example | |
5714 | ||
5715 | Remove the top entry from the directory stack, and @code{cd} | |
5716 | to the new top directory. | |
5717 | When no arguments are given, @code{popd} | |
5718 | removes the top directory from the stack and | |
5719 | performs a @code{cd} to the new top directory. The | |
5720 | elements are numbered from 0 starting at the first directory listed with | |
5721 | @code{dirs}; i.e., @code{popd} is equivalent to @code{popd +0}. | |
5722 | @table @code | |
5723 | @item +@var{N} | |
5724 | Removes the @var{N}th directory (counting from the left of the | |
5725 | list printed by @code{dirs}), starting with zero. | |
5726 | @item -@var{N} | |
5727 | Removes the @var{N}th directory (counting from the right of the | |
5728 | list printed by @code{dirs}), starting with zero. | |
5729 | @item -n | |
5730 | Suppresses the normal change of directory when removing directories | |
5731 | from the stack, so that only the stack is manipulated. | |
5732 | @end table | |
5733 | ||
5734 | @btindex pushd | |
5735 | @item pushd | |
5736 | @example | |
5737 | pushd [@var{dir} | @var{+N} | @var{-N}] [-n] | |
5738 | @end example | |
5739 | ||
5740 | Save the current directory on the top of the directory stack | |
5741 | and then @code{cd} to @var{dir}. | |
5742 | With no arguments, @code{pushd} exchanges the top two directories. | |
5743 | ||
5744 | @table @code | |
5745 | @item +@var{N} | |
5746 | Brings the @var{N}th directory (counting from the left of the | |
5747 | list printed by @code{dirs}, starting with zero) to the top of | |
5748 | the list by rotating the stack. | |
5749 | @item -@var{N} | |
5750 | Brings the @var{N}th directory (counting from the right of the | |
5751 | list printed by @code{dirs}, starting with zero) to the top of | |
5752 | the list by rotating the stack. | |
5753 | @item -n | |
5754 | Suppresses the normal change of directory when adding directories | |
5755 | to the stack, so that only the stack is manipulated. | |
5756 | @item @var{dir} | |
5757 | Makes the current working directory be the top of the stack, and then | |
5758 | executes the equivalent of `@code{cd} @var{dir}'. | |
5759 | @code{cd}s to @var{dir}. | |
5760 | @end table | |
5761 | ||
5762 | @end table | |
5763 | ||
5764 | @node Printing a Prompt | |
5765 | @section Controlling the Prompt | |
5766 | @cindex prompting | |
ccc6cda3 | 5767 | |
28ef6c31 JA |
5768 | The value of the variable @env{PROMPT_COMMAND} is examined just before |
5769 | Bash prints each primary prompt. If @env{PROMPT_COMMAND} is set and | |
bb70624e JA |
5770 | has a non-null value, then the |
5771 | value is executed just as if it had been typed on the command line. | |
ccc6cda3 | 5772 | |
bb70624e JA |
5773 | In addition, the following table describes the special characters which |
5774 | can appear in the prompt variables: | |
ccc6cda3 | 5775 | |
bb70624e JA |
5776 | @table @code |
5777 | @item \a | |
5778 | A bell character. | |
5779 | @item \d | |
5780 | The date, in "Weekday Month Date" format (e.g., "Tue May 26"). | |
7117c2d2 JA |
5781 | @item \D@{@var{format}@} |
5782 | The @var{format} is passed to @code{strftime}(3) and the result is inserted | |
5783 | into the prompt string; an empty @var{format} results in a locale-specific | |
5784 | time representation. The braces are required. | |
bb70624e JA |
5785 | @item \e |
5786 | An escape character. | |
5787 | @item \h | |
5788 | The hostname, up to the first `.'. | |
5789 | @item \H | |
5790 | The hostname. | |
5791 | @item \j | |
5792 | The number of jobs currently managed by the shell. | |
5793 | @item \l | |
5794 | The basename of the shell's terminal device name. | |
5795 | @item \n | |
5796 | A newline. | |
5797 | @item \r | |
5798 | A carriage return. | |
5799 | @item \s | |
5800 | The name of the shell, the basename of @code{$0} (the portion | |
5801 | following the final slash). | |
5802 | @item \t | |
5803 | The time, in 24-hour HH:MM:SS format. | |
5804 | @item \T | |
5805 | The time, in 12-hour HH:MM:SS format. | |
5806 | @item \@@ | |
5807 | The time, in 12-hour am/pm format. | |
f73dda09 JA |
5808 | @item \A |
5809 | The time, in 24-hour HH:MM format. | |
bb70624e JA |
5810 | @item \u |
5811 | The username of the current user. | |
5812 | @item \v | |
5813 | The version of Bash (e.g., 2.00) | |
5814 | @item \V | |
5815 | The release of Bash, version + patchlevel (e.g., 2.00.0) | |
5816 | @item \w | |
b80f6443 | 5817 | The current working directory, with @env{$HOME} abbreviated with a tilde. |
bb70624e | 5818 | @item \W |
b80f6443 | 5819 | The basename of @env{$PWD}, with @env{$HOME} abbreviated with a tilde. |
bb70624e JA |
5820 | @item \! |
5821 | The history number of this command. | |
5822 | @item \# | |
5823 | The command number of this command. | |
5824 | @item \$ | |
5825 | If the effective uid is 0, @code{#}, otherwise @code{$}. | |
5826 | @item \@var{nnn} | |
5827 | The character whose ASCII code is the octal value @var{nnn}. | |
5828 | @item \\ | |
5829 | A backslash. | |
5830 | @item \[ | |
5831 | Begin a sequence of non-printing characters. This could be used to | |
5832 | embed a terminal control sequence into the prompt. | |
5833 | @item \] | |
5834 | End a sequence of non-printing characters. | |
5835 | @end table | |
ccc6cda3 | 5836 | |
bb70624e JA |
5837 | The command number and the history number are usually different: |
5838 | the history number of a command is its position in the history | |
5839 | list, which may include commands restored from the history file | |
5840 | (@pxref{Bash History Facilities}), while the command number is | |
5841 | the position in the sequence of commands executed during the current | |
5842 | shell session. | |
ccc6cda3 | 5843 | |
bb70624e JA |
5844 | After the string is decoded, it is expanded via |
5845 | parameter expansion, command substitution, arithmetic | |
5846 | expansion, and quote removal, subject to the value of the | |
5847 | @code{promptvars} shell option (@pxref{Bash Builtins}). | |
ccc6cda3 | 5848 | |
bb70624e JA |
5849 | @node The Restricted Shell |
5850 | @section The Restricted Shell | |
5851 | @cindex restricted shell | |
ccc6cda3 | 5852 | |
bb70624e | 5853 | If Bash is started with the name @code{rbash}, or the |
28ef6c31 | 5854 | @option{--restricted} |
7117c2d2 JA |
5855 | or |
5856 | @option{-r} | |
bb70624e JA |
5857 | option is supplied at invocation, the shell becomes restricted. |
5858 | A restricted shell is used to | |
5859 | set up an environment more controlled than the standard shell. | |
5860 | A restricted shell behaves identically to @code{bash} | |
7117c2d2 JA |
5861 | with the exception that the following are disallowed or not performed: |
5862 | ||
bb70624e JA |
5863 | @itemize @bullet |
5864 | @item | |
5865 | Changing directories with the @code{cd} builtin. | |
5866 | @item | |
28ef6c31 JA |
5867 | Setting or unsetting the values of the @env{SHELL}, @env{PATH}, |
5868 | @env{ENV}, or @env{BASH_ENV} variables. | |
bb70624e JA |
5869 | @item |
5870 | Specifying command names containing slashes. | |
5871 | @item | |
5872 | Specifying a filename containing a slash as an argument to the @code{.} | |
5873 | builtin command. | |
5874 | @item | |
28ef6c31 | 5875 | Specifying a filename containing a slash as an argument to the @option{-p} |
bb70624e JA |
5876 | option to the @code{hash} builtin command. |
5877 | @item | |
5878 | Importing function definitions from the shell environment at startup. | |
5879 | @item | |
28ef6c31 | 5880 | Parsing the value of @env{SHELLOPTS} from the shell environment at startup. |
bb70624e JA |
5881 | @item |
5882 | Redirecting output using the @samp{>}, @samp{>|}, @samp{<>}, @samp{>&}, | |
5883 | @samp{&>}, and @samp{>>} redirection operators. | |
5884 | @item | |
5885 | Using the @code{exec} builtin to replace the shell with another command. | |
5886 | @item | |
5887 | Adding or deleting builtin commands with the | |
28ef6c31 | 5888 | @option{-f} and @option{-d} options to the @code{enable} builtin. |
bb70624e | 5889 | @item |
7117c2d2 JA |
5890 | Using the @code{enable} builtin command to enable disabled shell builtins. |
5891 | @item | |
28ef6c31 | 5892 | Specifying the @option{-p} option to the @code{command} builtin. |
bb70624e JA |
5893 | @item |
5894 | Turning off restricted mode with @samp{set +r} or @samp{set +o restricted}. | |
5895 | @end itemize | |
cce855bc | 5896 | |
7117c2d2 JA |
5897 | These restrictions are enforced after any startup files are read. |
5898 | ||
5899 | When a command that is found to be a shell script is executed | |
5900 | (@pxref{Shell Scripts}), @code{rbash} turns off any restrictions in | |
5901 | the shell spawned to execute the script. | |
5902 | ||
bb70624e JA |
5903 | @node Bash POSIX Mode |
5904 | @section Bash POSIX Mode | |
5905 | @cindex POSIX Mode | |
cce855bc | 5906 | |
28ef6c31 | 5907 | Starting Bash with the @option{--posix} command-line option or executing |
bb70624e | 5908 | @samp{set -o posix} while Bash is running will cause Bash to conform more |
0628567a | 5909 | closely to the @sc{posix} standard by changing the behavior to |
bb70624e | 5910 | match that specified by @sc{posix} in areas where the Bash default differs. |
ccc6cda3 | 5911 | |
7117c2d2 JA |
5912 | When invoked as @code{sh}, Bash enters @sc{posix} mode after reading the |
5913 | startup files. | |
5914 | ||
bb70624e | 5915 | The following list is what's changed when `@sc{posix} mode' is in effect: |
ccc6cda3 | 5916 | |
bb70624e JA |
5917 | @enumerate |
5918 | @item | |
5919 | When a command in the hash table no longer exists, Bash will re-search | |
28ef6c31 | 5920 | @env{$PATH} to find the new location. This is also available with |
bb70624e | 5921 | @samp{shopt -s checkhash}. |
ccc6cda3 | 5922 | |
bb70624e | 5923 | @item |
28ef6c31 JA |
5924 | The message printed by the job control code and builtins when a job |
5925 | exits with a non-zero status is `Done(status)'. | |
ccc6cda3 | 5926 | |
bb70624e JA |
5927 | @item |
5928 | The message printed by the job control code and builtins when a job | |
28ef6c31 JA |
5929 | is stopped is `Stopped(@var{signame})', where @var{signame} is, for |
5930 | example, @code{SIGTSTP}. | |
ccc6cda3 | 5931 | |
bb70624e | 5932 | @item |
95732b49 JA |
5933 | The @code{bg} builtin uses the required format to describe each job placed |
5934 | in the background, which does not include an indication of whether the job | |
5935 | is the current or previous job. | |
5936 | ||
5937 | @item | |
5938 | Reserved words appearing in a context where reserved words are recognized | |
5939 | do not undergo alias expansion. | |
ccc6cda3 | 5940 | |
bb70624e | 5941 | @item |
0628567a | 5942 | The @sc{posix} @env{PS1} and @env{PS2} expansions of @samp{!} to |
bb70624e | 5943 | the history number and @samp{!!} to @samp{!} are enabled, |
28ef6c31 JA |
5944 | and parameter expansion is performed on the values of @env{PS1} and |
5945 | @env{PS2} regardless of the setting of the @code{promptvars} option. | |
ccc6cda3 | 5946 | |
bb70624e | 5947 | @item |
0628567a | 5948 | The @sc{posix} startup files are executed (@env{$ENV}) rather than |
bb70624e | 5949 | the normal Bash files. |
ccc6cda3 | 5950 | |
bb70624e JA |
5951 | @item |
5952 | Tilde expansion is only performed on assignments preceding a command | |
5953 | name, rather than on all assignment statements on the line. | |
cce855bc | 5954 | |
bb70624e JA |
5955 | @item |
5956 | The default history file is @file{~/.sh_history} (this is the | |
28ef6c31 | 5957 | default value of @env{$HISTFILE}). |
ccc6cda3 | 5958 | |
bb70624e JA |
5959 | @item |
5960 | The output of @samp{kill -l} prints all the signal names on a single line, | |
b80f6443 JA |
5961 | separated by spaces, without the @samp{SIG} prefix. |
5962 | ||
5963 | @item | |
5964 | The @code{kill} builtin does not accept signal names with a @samp{SIG} | |
5965 | prefix. | |
ccc6cda3 | 5966 | |
bb70624e JA |
5967 | @item |
5968 | Non-interactive shells exit if @var{filename} in @code{.} @var{filename} | |
5969 | is not found. | |
ccc6cda3 | 5970 | |
bb70624e JA |
5971 | @item |
5972 | Non-interactive shells exit if a syntax error in an arithmetic expansion | |
5973 | results in an invalid expression. | |
ccc6cda3 | 5974 | |
bb70624e JA |
5975 | @item |
5976 | Redirection operators do not perform filename expansion on the word | |
5977 | in the redirection unless the shell is interactive. | |
ccc6cda3 | 5978 | |
bb70624e JA |
5979 | @item |
5980 | Redirection operators do not perform word splitting on the word in the | |
5981 | redirection. | |
ccc6cda3 | 5982 | |
bb70624e JA |
5983 | @item |
5984 | Function names must be valid shell @code{name}s. That is, they may not | |
5985 | contain characters other than letters, digits, and underscores, and | |
5986 | may not start with a digit. Declaring a function with an invalid name | |
5987 | causes a fatal syntax error in non-interactive shells. | |
ccc6cda3 | 5988 | |
bb70624e | 5989 | @item |
0628567a | 5990 | @sc{posix} special builtins are found before shell functions |
bb70624e | 5991 | during command lookup. |
cce855bc | 5992 | |
bb70624e | 5993 | @item |
0628567a | 5994 | If a @sc{posix} special builtin returns an error status, a |
bb70624e | 5995 | non-interactive shell exits. The fatal errors are those listed in |
0628567a | 5996 | the POSIX standard, and include things like passing incorrect options, |
bb70624e JA |
5997 | redirection errors, variable assignment errors for assignments preceding |
5998 | the command name, and so on. | |
ccc6cda3 | 5999 | |
bb70624e | 6000 | @item |
28ef6c31 | 6001 | If @env{CDPATH} is set, the @code{cd} builtin will not implicitly |
bb70624e JA |
6002 | append the current directory to it. This means that @code{cd} will |
6003 | fail if no valid directory name can be constructed from | |
28ef6c31 | 6004 | any of the entries in @env{$CDPATH}, even if the a directory with |
bb70624e JA |
6005 | the same name as the name given as an argument to @code{cd} exists |
6006 | in the current directory. | |
ccc6cda3 | 6007 | |
bb70624e JA |
6008 | @item |
6009 | A non-interactive shell exits with an error status if a variable | |
6010 | assignment error occurs when no command name follows the assignment | |
6011 | statements. | |
6012 | A variable assignment error occurs, for example, when trying to assign | |
6013 | a value to a readonly variable. | |
ccc6cda3 | 6014 | |
bb70624e JA |
6015 | @item |
6016 | A non-interactive shell exits with an error status if the iteration | |
6017 | variable in a @code{for} statement or the selection variable in a | |
6018 | @code{select} statement is a readonly variable. | |
ccc6cda3 | 6019 | |
bb70624e JA |
6020 | @item |
6021 | Process substitution is not available. | |
ccc6cda3 | 6022 | |
bb70624e | 6023 | @item |
0628567a | 6024 | Assignment statements preceding @sc{posix} special builtins |
bb70624e | 6025 | persist in the shell environment after the builtin completes. |
ccc6cda3 | 6026 | |
28ef6c31 JA |
6027 | @item |
6028 | Assignment statements preceding shell function calls persist in the | |
6029 | shell environment after the function returns, as if a @sc{posix} | |
6030 | special builtin command had been executed. | |
6031 | ||
bb70624e JA |
6032 | @item |
6033 | The @code{export} and @code{readonly} builtin commands display their | |
0628567a | 6034 | output in the format required by @sc{posix}. |
ccc6cda3 | 6035 | |
28ef6c31 JA |
6036 | @item |
6037 | The @code{trap} builtin displays signal names without the leading | |
6038 | @code{SIG}. | |
6039 | ||
b80f6443 JA |
6040 | @item |
6041 | The @code{trap} builtin doesn't check the first argument for a possible | |
6042 | signal specification and revert the signal handling to the original | |
eb873671 JA |
6043 | disposition if it is, unless that argument consists solely of digits and |
6044 | is a valid signal number. If users want to reset the handler for a given | |
b80f6443 JA |
6045 | signal to the original disposition, they should use @samp{-} as the |
6046 | first argument. | |
6047 | ||
28ef6c31 JA |
6048 | @item |
6049 | The @code{.} and @code{source} builtins do not search the current directory | |
6050 | for the filename argument if it is not found by searching @env{PATH}. | |
6051 | ||
6052 | @item | |
6053 | Subshells spawned to execute command substitutions inherit the value of | |
6054 | the @option{-e} option from the parent shell. When not in @sc{posix} mode, | |
6055 | Bash clears the @option{-e} option in such subshells. | |
6056 | ||
6057 | @item | |
6058 | Alias expansion is always enabled, even in non-interactive shells. | |
6059 | ||
b80f6443 JA |
6060 | @item |
6061 | When the @code{alias} builtin displays alias definitions, it does not | |
6062 | display them with a leading @samp{alias } unless the @option{-p} option | |
6063 | is supplied. | |
6064 | ||
28ef6c31 JA |
6065 | @item |
6066 | When the @code{set} builtin is invoked without options, it does not display | |
6067 | shell function names and definitions. | |
6068 | ||
f73dda09 JA |
6069 | @item |
6070 | When the @code{set} builtin is invoked without options, it displays | |
6071 | variable values without quotes, unless they contain shell metacharacters, | |
6072 | even if the result contains nonprinting characters. | |
7117c2d2 JA |
6073 | |
6074 | @item | |
6075 | When the @code{cd} builtin is invoked in @var{logical} mode, and the pathname | |
6076 | constructed from @code{$PWD} and the directory name supplied as an argument | |
6077 | does not refer to an existing directory, @code{cd} will fail instead of | |
6078 | falling back to @var{physical} mode. | |
95732b49 JA |
6079 | |
6080 | @item | |
6081 | When the @code{pwd} builtin is supplied the @option{-P} option, it resets | |
6082 | @code{$PWD} to a pathname containing no symlinks. | |
6083 | ||
6084 | @item | |
6085 | The @code{pwd} builtin verifies that the value it prints is the same as the | |
6086 | current directory, even if it is not asked to check the file system with the | |
6087 | @option{-P} option. | |
6088 | ||
6089 | @item | |
6090 | When listing the history, the @code{fc} builtin does not include an | |
6091 | indication of whether or not a history entry has been modified. | |
6092 | ||
6093 | @item | |
6094 | The default editor used by @code{fc} is @code{ed}. | |
6095 | ||
6096 | @item | |
6097 | The @code{type} and @code{command} builtins will not report a non-executable | |
6098 | file as having been found, though the shell will attempt to execute such a | |
6099 | file if it is the only so-named file found in @code{$PATH}. | |
6100 | ||
6101 | @item | |
6102 | The @code{vi} editing mode will invoke the @code{vi} editor directly when | |
6103 | the @samp{v} command is run, instead of checking @code{$FCEDIT} and | |
6104 | @code{$EDITOR}. | |
6105 | ||
6106 | @item | |
6107 | When the @code{xpg_echo} option is enabled, Bash does not attempt to interpret | |
6108 | any arguments to @code{echo} as options. Each argument is displayed, after | |
6109 | escape characters are converted. | |
6110 | ||
bb70624e | 6111 | @end enumerate |
ccc6cda3 | 6112 | |
0628567a | 6113 | There is other @sc{posix} behavior that Bash does not implement by |
95732b49 | 6114 | default even when in @sc{posix} mode. |
bb70624e | 6115 | Specifically: |
ccc6cda3 | 6116 | |
bb70624e | 6117 | @enumerate |
28ef6c31 JA |
6118 | |
6119 | @item | |
95732b49 JA |
6120 | The @code{fc} builtin checks @code{$EDITOR} as a program to edit history |
6121 | entries if @code{FCEDIT} is unset, rather than defaulting directly to | |
6122 | @code{ed}. @code{fc} uses @code{ed} if @code{EDITOR} is unset. | |
28ef6c31 JA |
6123 | |
6124 | @item | |
95732b49 JA |
6125 | As noted above, Bash requires the @code{xpg_echo} option to be enabled for |
6126 | the @code{echo} builtin to be fully conformant. | |
28ef6c31 | 6127 | |
bb70624e | 6128 | @end enumerate |
ccc6cda3 | 6129 | |
95732b49 JA |
6130 | Bash can be configured to be @sc{posix}-conformant by default, by specifying |
6131 | the @option{--enable-strict-posix-default} to @code{configure} when building | |
6132 | (@pxref{Optional Features}). | |
6133 | ||
bb70624e JA |
6134 | @node Job Control |
6135 | @chapter Job Control | |
ccc6cda3 | 6136 | |
bb70624e JA |
6137 | This chapter discusses what job control is, how it works, and how |
6138 | Bash allows you to access its facilities. | |
ccc6cda3 | 6139 | |
bb70624e JA |
6140 | @menu |
6141 | * Job Control Basics:: How job control works. | |
6142 | * Job Control Builtins:: Bash builtin commands used to interact | |
6143 | with job control. | |
6144 | * Job Control Variables:: Variables Bash uses to customize job | |
6145 | control. | |
6146 | @end menu | |
ccc6cda3 | 6147 | |
bb70624e JA |
6148 | @node Job Control Basics |
6149 | @section Job Control Basics | |
6150 | @cindex job control | |
6151 | @cindex foreground | |
6152 | @cindex background | |
6153 | @cindex suspending jobs | |
ccc6cda3 | 6154 | |
bb70624e JA |
6155 | Job control |
6156 | refers to the ability to selectively stop (suspend) | |
6157 | the execution of processes and continue (resume) | |
6158 | their execution at a later point. A user typically employs | |
6159 | this facility via an interactive interface supplied jointly | |
6160 | by the system's terminal driver and Bash. | |
ccc6cda3 | 6161 | |
bb70624e JA |
6162 | The shell associates a @var{job} with each pipeline. It keeps a |
6163 | table of currently executing jobs, which may be listed with the | |
6164 | @code{jobs} command. When Bash starts a job | |
6165 | asynchronously, it prints a line that looks | |
6166 | like: | |
6167 | @example | |
6168 | [1] 25647 | |
6169 | @end example | |
6170 | @noindent | |
6171 | indicating that this job is job number 1 and that the process @sc{id} | |
6172 | of the last process in the pipeline associated with this job is | |
6173 | 25647. All of the processes in a single pipeline are members of | |
6174 | the same job. Bash uses the @var{job} abstraction as the | |
6175 | basis for job control. | |
ccc6cda3 | 6176 | |
bb70624e JA |
6177 | To facilitate the implementation of the user interface to job |
6178 | control, the operating system maintains the notion of a current terminal | |
6179 | process group @sc{id}. Members of this process group (processes whose | |
6180 | process group @sc{id} is equal to the current terminal process group | |
6181 | @sc{id}) receive keyboard-generated signals such as @code{SIGINT}. | |
6182 | These processes are said to be in the foreground. Background | |
6183 | processes are those whose process group @sc{id} differs from the | |
6184 | terminal's; such processes are immune to keyboard-generated | |
6185 | signals. Only foreground processes are allowed to read from or | |
6186 | write to the terminal. Background processes which attempt to | |
6187 | read from (write to) the terminal are sent a @code{SIGTTIN} | |
6188 | (@code{SIGTTOU}) signal by the terminal driver, which, unless | |
6189 | caught, suspends the process. | |
ccc6cda3 | 6190 | |
bb70624e JA |
6191 | If the operating system on which Bash is running supports |
6192 | job control, Bash contains facilities to use it. Typing the | |
6193 | @var{suspend} character (typically @samp{^Z}, Control-Z) while a | |
6194 | process is running causes that process to be stopped and returns | |
6195 | control to Bash. Typing the @var{delayed suspend} character | |
6196 | (typically @samp{^Y}, Control-Y) causes the process to be stopped | |
6197 | when it attempts to read input from the terminal, and control to | |
6198 | be returned to Bash. The user then manipulates the state of | |
6199 | this job, using the @code{bg} command to continue it in the | |
6200 | background, the @code{fg} command to continue it in the | |
6201 | foreground, or the @code{kill} command to kill it. A @samp{^Z} | |
6202 | takes effect immediately, and has the additional side effect of | |
6203 | causing pending output and typeahead to be discarded. | |
ccc6cda3 | 6204 | |
bb70624e JA |
6205 | There are a number of ways to refer to a job in the shell. The |
6206 | character @samp{%} introduces a job name. | |
cce855bc | 6207 | |
bb70624e | 6208 | Job number @code{n} may be referred to as @samp{%n}. |
95732b49 JA |
6209 | The symbols @samp{%%} and @samp{%+} refer to the shell's notion of the |
6210 | current job, which is the last job stopped while it was in the foreground | |
6211 | or started in the background. | |
6212 | A single @samp{%} (with no accompanying job specification) also refers | |
6213 | to the current job. | |
6214 | The previous job may be referenced using @samp{%-}. In output | |
bb70624e JA |
6215 | pertaining to jobs (e.g., the output of the @code{jobs} command), |
6216 | the current job is always flagged with a @samp{+}, and the | |
6217 | previous job with a @samp{-}. | |
cce855bc | 6218 | |
bb70624e JA |
6219 | A job may also be referred to |
6220 | using a prefix of the name used to start it, or using a substring | |
6221 | that appears in its command line. For example, @samp{%ce} refers | |
6222 | to a stopped @code{ce} job. Using @samp{%?ce}, on the | |
6223 | other hand, refers to any job containing the string @samp{ce} in | |
6224 | its command line. If the prefix or substring matches more than one job, | |
6225 | Bash reports an error. | |
cce855bc | 6226 | |
bb70624e JA |
6227 | Simply naming a job can be used to bring it into the foreground: |
6228 | @samp{%1} is a synonym for @samp{fg %1}, bringing job 1 from the | |
6229 | background into the foreground. Similarly, @samp{%1 &} resumes | |
6230 | job 1 in the background, equivalent to @samp{bg %1} | |
cce855bc | 6231 | |
bb70624e JA |
6232 | The shell learns immediately whenever a job changes state. |
6233 | Normally, Bash waits until it is about to print a prompt | |
6234 | before reporting changes in a job's status so as to not interrupt | |
f73dda09 JA |
6235 | any other output. |
6236 | If the @option{-b} option to the @code{set} builtin is enabled, | |
bb70624e | 6237 | Bash reports such changes immediately (@pxref{The Set Builtin}). |
f73dda09 JA |
6238 | Any trap on @code{SIGCHLD} is executed for each child process |
6239 | that exits. | |
ccc6cda3 | 6240 | |
b80f6443 | 6241 | If an attempt to exit Bash is made while jobs are stopped, the |
bb70624e JA |
6242 | shell prints a message warning that there are stopped jobs. |
6243 | The @code{jobs} command may then be used to inspect their status. | |
6244 | If a second attempt to exit is made without an intervening command, | |
6245 | Bash does not print another warning, and the stopped jobs are terminated. | |
ccc6cda3 | 6246 | |
bb70624e JA |
6247 | @node Job Control Builtins |
6248 | @section Job Control Builtins | |
ccc6cda3 JA |
6249 | |
6250 | @table @code | |
6251 | ||
bb70624e JA |
6252 | @item bg |
6253 | @btindex bg | |
ccc6cda3 | 6254 | @example |
95732b49 | 6255 | bg [@var{jobspec} @dots{}] |
ccc6cda3 | 6256 | @end example |
95732b49 | 6257 | Resume each suspended job @var{jobspec} in the background, as if it |
bb70624e JA |
6258 | had been started with @samp{&}. |
6259 | If @var{jobspec} is not supplied, the current job is used. | |
6260 | The return status is zero unless it is run when job control is not | |
95732b49 JA |
6261 | enabled, or, when run with job control enabled, any |
6262 | @var{jobspec} was not found or specifies a job | |
6263 | that was started without job control. | |
cce855bc | 6264 | |
bb70624e JA |
6265 | @item fg |
6266 | @btindex fg | |
6267 | @example | |
6268 | fg [@var{jobspec}] | |
6269 | @end example | |
6270 | Resume the job @var{jobspec} in the foreground and make it the current job. | |
6271 | If @var{jobspec} is not supplied, the current job is used. | |
6272 | The return status is that of the command placed into the foreground, | |
6273 | or non-zero if run when job control is disabled or, when run with | |
6274 | job control enabled, @var{jobspec} does not specify a valid job or | |
6275 | @var{jobspec} specifies a job that was started without job control. | |
cce855bc | 6276 | |
bb70624e JA |
6277 | @item jobs |
6278 | @btindex jobs | |
cce855bc | 6279 | @example |
bb70624e JA |
6280 | jobs [-lnprs] [@var{jobspec}] |
6281 | jobs -x @var{command} [@var{arguments}] | |
cce855bc JA |
6282 | @end example |
6283 | ||
bb70624e JA |
6284 | The first form lists the active jobs. The options have the |
6285 | following meanings: | |
6286 | ||
6287 | @table @code | |
6288 | @item -l | |
6289 | List process @sc{id}s in addition to the normal information. | |
6290 | ||
6291 | @item -n | |
6292 | Display information only about jobs that have changed status since | |
6293 | the user was last notified of their status. | |
6294 | ||
6295 | @item -p | |
6296 | List only the process @sc{id} of the job's process group leader. | |
6297 | ||
6298 | @item -r | |
6299 | Restrict output to running jobs. | |
6300 | ||
6301 | @item -s | |
6302 | Restrict output to stopped jobs. | |
ccc6cda3 JA |
6303 | @end table |
6304 | ||
bb70624e JA |
6305 | If @var{jobspec} is given, |
6306 | output is restricted to information about that job. | |
6307 | If @var{jobspec} is not supplied, the status of all jobs is | |
6308 | listed. | |
ccc6cda3 | 6309 | |
28ef6c31 | 6310 | If the @option{-x} option is supplied, @code{jobs} replaces any |
bb70624e JA |
6311 | @var{jobspec} found in @var{command} or @var{arguments} with the |
6312 | corresponding process group @sc{id}, and executes @var{command}, | |
6313 | passing it @var{argument}s, returning its exit status. | |
ccc6cda3 | 6314 | |
bb70624e JA |
6315 | @item kill |
6316 | @btindex kill | |
ccc6cda3 | 6317 | @example |
bb70624e JA |
6318 | kill [-s @var{sigspec}] [-n @var{signum}] [-@var{sigspec}] @var{jobspec} or @var{pid} |
6319 | kill -l [@var{exit_status}] | |
ccc6cda3 | 6320 | @end example |
bb70624e JA |
6321 | Send a signal specified by @var{sigspec} or @var{signum} to the process |
6322 | named by job specification @var{jobspec} or process @sc{id} @var{pid}. | |
b80f6443 JA |
6323 | @var{sigspec} is either a case-insensitive signal name such as |
6324 | @code{SIGINT} (with or without the @code{SIG} prefix) | |
6325 | or a signal number; @var{signum} is a signal number. | |
bb70624e | 6326 | If @var{sigspec} and @var{signum} are not present, @code{SIGTERM} is used. |
28ef6c31 JA |
6327 | The @option{-l} option lists the signal names. |
6328 | If any arguments are supplied when @option{-l} is given, the names of the | |
bb70624e JA |
6329 | signals corresponding to the arguments are listed, and the return status |
6330 | is zero. | |
6331 | @var{exit_status} is a number specifying a signal number or the exit | |
6332 | status of a process terminated by a signal. | |
6333 | The return status is zero if at least one signal was successfully sent, | |
6334 | or non-zero if an error occurs or an invalid option is encountered. | |
ccc6cda3 | 6335 | |
bb70624e JA |
6336 | @item wait |
6337 | @btindex wait | |
ccc6cda3 | 6338 | @example |
95732b49 | 6339 | wait [@var{jobspec} or @var{pid} ...] |
ccc6cda3 | 6340 | @end example |
95732b49 JA |
6341 | Wait until the child process specified by each process @sc{id} @var{pid} |
6342 | or job specification @var{jobspec} exits and return the exit status of the | |
6343 | last command waited for. | |
bb70624e JA |
6344 | If a job spec is given, all processes in the job are waited for. |
6345 | If no arguments are given, all currently active child processes are | |
6346 | waited for, and the return status is zero. | |
6347 | If neither @var{jobspec} nor @var{pid} specifies an active child process | |
6348 | of the shell, the return status is 127. | |
6349 | ||
6350 | @item disown | |
6351 | @btindex disown | |
ccc6cda3 | 6352 | @example |
bb70624e | 6353 | disown [-ar] [-h] [@var{jobspec} @dots{}] |
ccc6cda3 | 6354 | @end example |
bb70624e JA |
6355 | Without options, each @var{jobspec} is removed from the table of |
6356 | active jobs. | |
28ef6c31 | 6357 | If the @option{-h} option is given, the job is not removed from the table, |
bb70624e JA |
6358 | but is marked so that @code{SIGHUP} is not sent to the job if the shell |
6359 | receives a @code{SIGHUP}. | |
28ef6c31 | 6360 | If @var{jobspec} is not present, and neither the @option{-a} nor @option{-r} |
bb70624e | 6361 | option is supplied, the current job is used. |
28ef6c31 JA |
6362 | If no @var{jobspec} is supplied, the @option{-a} option means to remove or |
6363 | mark all jobs; the @option{-r} option without a @var{jobspec} | |
bb70624e | 6364 | argument restricts operation to running jobs. |
ccc6cda3 | 6365 | |
bb70624e JA |
6366 | @item suspend |
6367 | @btindex suspend | |
ccc6cda3 | 6368 | @example |
bb70624e | 6369 | suspend [-f] |
ccc6cda3 | 6370 | @end example |
bb70624e | 6371 | Suspend the execution of this shell until it receives a |
28ef6c31 | 6372 | @code{SIGCONT} signal. The @option{-f} option means to suspend |
bb70624e | 6373 | even if the shell is a login shell. |
ccc6cda3 | 6374 | |
bb70624e | 6375 | @end table |
ccc6cda3 | 6376 | |
bb70624e JA |
6377 | When job control is not active, the @code{kill} and @code{wait} |
6378 | builtins do not accept @var{jobspec} arguments. They must be | |
6379 | supplied process @sc{id}s. | |
ccc6cda3 | 6380 | |
bb70624e JA |
6381 | @node Job Control Variables |
6382 | @section Job Control Variables | |
ccc6cda3 | 6383 | |
bb70624e | 6384 | @vtable @code |
cce855bc | 6385 | |
bb70624e JA |
6386 | @item auto_resume |
6387 | This variable controls how the shell interacts with the user and | |
6388 | job control. If this variable exists then single word simple | |
6389 | commands without redirections are treated as candidates for resumption | |
6390 | of an existing job. There is no ambiguity allowed; if there is | |
6391 | more than one job beginning with the string typed, then | |
6392 | the most recently accessed job will be selected. | |
6393 | The name of a stopped job, in this context, is the command line | |
6394 | used to start it. If this variable is set to the value @samp{exact}, | |
6395 | the string supplied must match the name of a stopped job exactly; | |
6396 | if set to @samp{substring}, | |
6397 | the string supplied needs to match a substring of the name of a | |
6398 | stopped job. The @samp{substring} value provides functionality | |
6399 | analogous to the @samp{%?} job @sc{id} (@pxref{Job Control Basics}). | |
6400 | If set to any other value, the supplied string must | |
6401 | be a prefix of a stopped job's name; this provides functionality | |
6402 | analogous to the @samp{%} job @sc{id}. | |
cce855bc | 6403 | |
bb70624e | 6404 | @end vtable |
cce855bc | 6405 | |
bb70624e JA |
6406 | @set readline-appendix |
6407 | @set history-appendix | |
6408 | @cindex Readline, how to use | |
b80f6443 | 6409 | @include rluser.texi |
bb70624e | 6410 | @cindex History, how to use |
b80f6443 | 6411 | @include hsuser.texi |
bb70624e JA |
6412 | @clear readline-appendix |
6413 | @clear history-appendix | |
cce855bc | 6414 | |
bb70624e JA |
6415 | @node Installing Bash |
6416 | @chapter Installing Bash | |
cce855bc | 6417 | |
bb70624e JA |
6418 | This chapter provides basic instructions for installing Bash on |
6419 | the various supported platforms. The distribution supports the | |
6420 | @sc{gnu} operating systems, nearly every version of Unix, and several | |
6421 | non-Unix systems such as BeOS and Interix. | |
6422 | Other independent ports exist for | |
b80f6443 | 6423 | @sc{ms-dos}, @sc{os/2}, and Windows platforms. |
cce855bc | 6424 | |
bb70624e JA |
6425 | @menu |
6426 | * Basic Installation:: Installation instructions. | |
bb70624e JA |
6427 | * Compilers and Options:: How to set special options for various |
6428 | systems. | |
bb70624e JA |
6429 | * Compiling For Multiple Architectures:: How to compile Bash for more |
6430 | than one kind of system from | |
6431 | the same source tree. | |
bb70624e | 6432 | * Installation Names:: How to set the various paths used by the installation. |
bb70624e | 6433 | * Specifying the System Type:: How to configure Bash for a particular system. |
bb70624e JA |
6434 | * Sharing Defaults:: How to share default configuration values among GNU |
6435 | programs. | |
bb70624e | 6436 | * Operation Controls:: Options recognized by the configuration program. |
bb70624e JA |
6437 | * Optional Features:: How to enable and disable optional features when |
6438 | building Bash. | |
6439 | @end menu | |
ccc6cda3 | 6440 | |
bb70624e JA |
6441 | @node Basic Installation |
6442 | @section Basic Installation | |
6443 | @cindex installation | |
6444 | @cindex configuration | |
6445 | @cindex Bash installation | |
6446 | @cindex Bash configuration | |
ccc6cda3 | 6447 | |
bb70624e | 6448 | These are installation instructions for Bash. |
ccc6cda3 | 6449 | |
bb70624e | 6450 | The simplest way to compile Bash is: |
ccc6cda3 | 6451 | |
bb70624e | 6452 | @enumerate |
ccc6cda3 | 6453 | @item |
bb70624e JA |
6454 | @code{cd} to the directory containing the source code and type |
6455 | @samp{./configure} to configure Bash for your system. If you're | |
6456 | using @code{csh} on an old version of System V, you might need to | |
6457 | type @samp{sh ./configure} instead to prevent @code{csh} from trying | |
6458 | to execute @code{configure} itself. | |
6459 | ||
6460 | Running @code{configure} takes some time. | |
6461 | While running, it prints messages telling which features it is | |
6462 | checking for. | |
6463 | ||
ccc6cda3 | 6464 | @item |
bb70624e JA |
6465 | Type @samp{make} to compile Bash and build the @code{bashbug} bug |
6466 | reporting script. | |
6467 | ||
ccc6cda3 | 6468 | @item |
bb70624e JA |
6469 | Optionally, type @samp{make tests} to run the Bash test suite. |
6470 | ||
ccc6cda3 | 6471 | @item |
bb70624e JA |
6472 | Type @samp{make install} to install @code{bash} and @code{bashbug}. |
6473 | This will also install the manual pages and Info file. | |
ccc6cda3 | 6474 | |
bb70624e | 6475 | @end enumerate |
ccc6cda3 | 6476 | |
bb70624e JA |
6477 | The @code{configure} shell script attempts to guess correct |
6478 | values for various system-dependent variables used during | |
6479 | compilation. It uses those values to create a @file{Makefile} in | |
6480 | each directory of the package (the top directory, the | |
6481 | @file{builtins}, @file{doc}, and @file{support} directories, | |
6482 | each directory under @file{lib}, and several others). It also creates a | |
6483 | @file{config.h} file containing system-dependent definitions. | |
6484 | Finally, it creates a shell script named @code{config.status} that you | |
6485 | can run in the future to recreate the current configuration, a | |
6486 | file @file{config.cache} that saves the results of its tests to | |
6487 | speed up reconfiguring, and a file @file{config.log} containing | |
6488 | compiler output (useful mainly for debugging @code{configure}). | |
6489 | If at some point | |
6490 | @file{config.cache} contains results you don't want to keep, you | |
6491 | may remove or edit it. | |
ccc6cda3 | 6492 | |
bb70624e JA |
6493 | To find out more about the options and arguments that the |
6494 | @code{configure} script understands, type | |
ccc6cda3 | 6495 | |
bb70624e JA |
6496 | @example |
6497 | bash-2.04$ ./configure --help | |
6498 | @end example | |
ccc6cda3 | 6499 | |
bb70624e JA |
6500 | @noindent |
6501 | at the Bash prompt in your Bash source directory. | |
ccc6cda3 | 6502 | |
bb70624e JA |
6503 | If you need to do unusual things to compile Bash, please |
6504 | try to figure out how @code{configure} could check whether or not | |
6505 | to do them, and mail diffs or instructions to | |
6506 | @email{bash-maintainers@@gnu.org} so they can be | |
6507 | considered for the next release. | |
ccc6cda3 | 6508 | |
bb70624e JA |
6509 | The file @file{configure.in} is used to create @code{configure} |
6510 | by a program called Autoconf. You only need | |
6511 | @file{configure.in} if you want to change it or regenerate | |
6512 | @code{configure} using a newer version of Autoconf. If | |
f73dda09 | 6513 | you do this, make sure you are using Autoconf version 2.50 or |
bb70624e | 6514 | newer. |
ccc6cda3 | 6515 | |
bb70624e JA |
6516 | You can remove the program binaries and object files from the |
6517 | source code directory by typing @samp{make clean}. To also remove the | |
6518 | files that @code{configure} created (so you can compile Bash for | |
6519 | a different kind of computer), type @samp{make distclean}. | |
ccc6cda3 | 6520 | |
bb70624e JA |
6521 | @node Compilers and Options |
6522 | @section Compilers and Options | |
ccc6cda3 | 6523 | |
bb70624e JA |
6524 | Some systems require unusual options for compilation or linking |
6525 | that the @code{configure} script does not know about. You can | |
6526 | give @code{configure} initial values for variables by setting | |
6527 | them in the environment. Using a Bourne-compatible shell, you | |
6528 | can do that on the command line like this: | |
ccc6cda3 | 6529 | |
bb70624e JA |
6530 | @example |
6531 | CC=c89 CFLAGS=-O2 LIBS=-lposix ./configure | |
6532 | @end example | |
ccc6cda3 | 6533 | |
bb70624e | 6534 | On systems that have the @code{env} program, you can do it like this: |
ccc6cda3 | 6535 | |
bb70624e JA |
6536 | @example |
6537 | env CPPFLAGS=-I/usr/local/include LDFLAGS=-s ./configure | |
6538 | @end example | |
ccc6cda3 | 6539 | |
bb70624e JA |
6540 | The configuration process uses GCC to build Bash if it |
6541 | is available. | |
cce855bc | 6542 | |
bb70624e JA |
6543 | @node Compiling For Multiple Architectures |
6544 | @section Compiling For Multiple Architectures | |
ccc6cda3 | 6545 | |
bb70624e JA |
6546 | You can compile Bash for more than one kind of computer at the |
6547 | same time, by placing the object files for each architecture in their | |
6548 | own directory. To do this, you must use a version of @code{make} that | |
6549 | supports the @code{VPATH} variable, such as GNU @code{make}. | |
6550 | @code{cd} to the | |
6551 | directory where you want the object files and executables to go and run | |
6552 | the @code{configure} script from the source directory. You may need to | |
28ef6c31 | 6553 | supply the @option{--srcdir=PATH} argument to tell @code{configure} where the |
bb70624e JA |
6554 | source files are. @code{configure} automatically checks for the |
6555 | source code in the directory that @code{configure} is in and in `..'. | |
ccc6cda3 | 6556 | |
bb70624e JA |
6557 | If you have to use a @code{make} that does not supports the @code{VPATH} |
6558 | variable, you can compile Bash for one architecture at a | |
6559 | time in the source code directory. After you have installed | |
6560 | Bash for one architecture, use @samp{make distclean} before | |
6561 | reconfiguring for another architecture. | |
ccc6cda3 | 6562 | |
bb70624e JA |
6563 | Alternatively, if your system supports symbolic links, you can use the |
6564 | @file{support/mkclone} script to create a build tree which has | |
6565 | symbolic links back to each file in the source directory. Here's an | |
6566 | example that creates a build directory in the current directory from a | |
6567 | source directory @file{/usr/gnu/src/bash-2.0}: | |
6568 | ||
6569 | @example | |
6570 | bash /usr/gnu/src/bash-2.0/support/mkclone -s /usr/gnu/src/bash-2.0 . | |
6571 | @end example | |
6572 | ||
6573 | @noindent | |
6574 | The @code{mkclone} script requires Bash, so you must have already built | |
6575 | Bash for at least one architecture before you can create build | |
6576 | directories for other architectures. | |
6577 | ||
6578 | @node Installation Names | |
6579 | @section Installation Names | |
ccc6cda3 | 6580 | |
bb70624e JA |
6581 | By default, @samp{make install} will install into |
6582 | @file{/usr/local/bin}, @file{/usr/local/man}, etc. You can | |
6583 | specify an installation prefix other than @file{/usr/local} by | |
f73dda09 JA |
6584 | giving @code{configure} the option @option{--prefix=@var{PATH}}, |
6585 | or by specifying a value for the @code{DESTDIR} @samp{make} | |
6586 | variable when running @samp{make install}. | |
ccc6cda3 | 6587 | |
bb70624e JA |
6588 | You can specify separate installation prefixes for |
6589 | architecture-specific files and architecture-independent files. | |
6590 | If you give @code{configure} the option | |
28ef6c31 | 6591 | @option{--exec-prefix=@var{PATH}}, @samp{make install} will use |
bb70624e JA |
6592 | @var{PATH} as the prefix for installing programs and libraries. |
6593 | Documentation and other data files will still use the regular prefix. | |
cce855bc | 6594 | |
bb70624e JA |
6595 | @node Specifying the System Type |
6596 | @section Specifying the System Type | |
ccc6cda3 | 6597 | |
bb70624e | 6598 | There may be some features @code{configure} can not figure out |
f73dda09 | 6599 | automatically, but need to determine by the type of host Bash |
bb70624e JA |
6600 | will run on. Usually @code{configure} can figure that |
6601 | out, but if it prints a message saying it can not guess the host | |
28ef6c31 | 6602 | type, give it the @option{--host=TYPE} option. @samp{TYPE} can |
bb70624e JA |
6603 | either be a short name for the system type, such as @samp{sun4}, |
6604 | or a canonical name with three fields: @samp{CPU-COMPANY-SYSTEM} | |
f73dda09 | 6605 | (e.g., @samp{i386-unknown-freebsd4.2}). |
ccc6cda3 | 6606 | |
bb70624e JA |
6607 | See the file @file{support/config.sub} for the possible |
6608 | values of each field. | |
ccc6cda3 | 6609 | |
bb70624e JA |
6610 | @node Sharing Defaults |
6611 | @section Sharing Defaults | |
ccc6cda3 | 6612 | |
bb70624e JA |
6613 | If you want to set default values for @code{configure} scripts to |
6614 | share, you can create a site shell script called | |
6615 | @code{config.site} that gives default values for variables like | |
6616 | @code{CC}, @code{cache_file}, and @code{prefix}. @code{configure} | |
6617 | looks for @file{PREFIX/share/config.site} if it exists, then | |
6618 | @file{PREFIX/etc/config.site} if it exists. Or, you can set the | |
6619 | @code{CONFIG_SITE} environment variable to the location of the site | |
6620 | script. A warning: the Bash @code{configure} looks for a site script, | |
6621 | but not all @code{configure} scripts do. | |
d166f048 | 6622 | |
bb70624e JA |
6623 | @node Operation Controls |
6624 | @section Operation Controls | |
ccc6cda3 | 6625 | |
bb70624e JA |
6626 | @code{configure} recognizes the following options to control how it |
6627 | operates. | |
ccc6cda3 | 6628 | |
bb70624e | 6629 | @table @code |
ccc6cda3 | 6630 | |
bb70624e JA |
6631 | @item --cache-file=@var{file} |
6632 | Use and save the results of the tests in | |
6633 | @var{file} instead of @file{./config.cache}. Set @var{file} to | |
6634 | @file{/dev/null} to disable caching, for debugging | |
6635 | @code{configure}. | |
ccc6cda3 | 6636 | |
bb70624e JA |
6637 | @item --help |
6638 | Print a summary of the options to @code{configure}, and exit. | |
ccc6cda3 | 6639 | |
bb70624e JA |
6640 | @item --quiet |
6641 | @itemx --silent | |
6642 | @itemx -q | |
6643 | Do not print messages saying which checks are being made. | |
ccc6cda3 | 6644 | |
bb70624e JA |
6645 | @item --srcdir=@var{dir} |
6646 | Look for the Bash source code in directory @var{dir}. Usually | |
6647 | @code{configure} can determine that directory automatically. | |
ccc6cda3 | 6648 | |
bb70624e JA |
6649 | @item --version |
6650 | Print the version of Autoconf used to generate the @code{configure} | |
6651 | script, and exit. | |
6652 | @end table | |
ccc6cda3 | 6653 | |
bb70624e JA |
6654 | @code{configure} also accepts some other, not widely used, boilerplate |
6655 | options. @samp{configure --help} prints the complete list. | |
ccc6cda3 | 6656 | |
bb70624e JA |
6657 | @node Optional Features |
6658 | @section Optional Features | |
ccc6cda3 | 6659 | |
28ef6c31 | 6660 | The Bash @code{configure} has a number of @option{--enable-@var{feature}} |
bb70624e | 6661 | options, where @var{feature} indicates an optional part of Bash. |
28ef6c31 | 6662 | There are also several @option{--with-@var{package}} options, |
bb70624e JA |
6663 | where @var{package} is something like @samp{bash-malloc} or @samp{purify}. |
6664 | To turn off the default use of a package, use | |
28ef6c31 JA |
6665 | @option{--without-@var{package}}. To configure Bash without a feature |
6666 | that is enabled by default, use @option{--disable-@var{feature}}. | |
ccc6cda3 | 6667 | |
28ef6c31 JA |
6668 | Here is a complete list of the @option{--enable-} and |
6669 | @option{--with-} options that the Bash @code{configure} recognizes. | |
ccc6cda3 | 6670 | |
bb70624e JA |
6671 | @table @code |
6672 | @item --with-afs | |
6673 | Define if you are using the Andrew File System from Transarc. | |
ccc6cda3 | 6674 | |
bb70624e JA |
6675 | @item --with-bash-malloc |
6676 | Use the Bash version of | |
95732b49 | 6677 | @code{malloc} in the directory @file{lib/malloc}. This is not the same |
bb70624e | 6678 | @code{malloc} that appears in @sc{gnu} libc, but an older version |
95732b49 JA |
6679 | originally derived from the 4.2 @sc{bsd} @code{malloc}. This @code{malloc} |
6680 | is very fast, but wastes some space on each allocation. | |
bb70624e JA |
6681 | This option is enabled by default. |
6682 | The @file{NOTES} file contains a list of systems for | |
6683 | which this should be turned off, and @code{configure} disables this | |
6684 | option automatically for a number of systems. | |
ccc6cda3 | 6685 | |
bb70624e JA |
6686 | @item --with-curses |
6687 | Use the curses library instead of the termcap library. This should | |
6688 | be supplied if your system has an inadequate or incomplete termcap | |
6689 | database. | |
ccc6cda3 | 6690 | |
bb70624e JA |
6691 | @item --with-gnu-malloc |
6692 | A synonym for @code{--with-bash-malloc}. | |
ccc6cda3 | 6693 | |
f73dda09 | 6694 | @item --with-installed-readline[=@var{PREFIX}] |
bb70624e JA |
6695 | Define this to make Bash link with a locally-installed version of Readline |
6696 | rather than the version in @file{lib/readline}. This works only with | |
95732b49 | 6697 | Readline 5.0 and later versions. If @var{PREFIX} is @code{yes} or not |
f73dda09 JA |
6698 | supplied, @code{configure} uses the values of the make variables |
6699 | @code{includedir} and @code{libdir}, which are subdirectories of @code{prefix} | |
6700 | by default, to find the installed version of Readline if it is not in | |
6701 | the standard system include and library directories. | |
6702 | If @var{PREFIX} is @code{no}, Bash links with the version in | |
6703 | @file{lib/readline}. | |
6704 | If @var{PREFIX} is set to any other value, @code{configure} treats it as | |
6705 | a directory pathname and looks for | |
6706 | the installed version of Readline in subdirectories of that directory | |
6707 | (include files in @var{PREFIX}/@code{include} and the library in | |
6708 | @var{PREFIX}/@code{lib}). | |
ccc6cda3 | 6709 | |
bb70624e JA |
6710 | @item --with-purify |
6711 | Define this to use the Purify memory allocation checker from Rational | |
6712 | Software. | |
ccc6cda3 | 6713 | |
bb70624e JA |
6714 | @item --enable-minimal-config |
6715 | This produces a shell with minimal features, close to the historical | |
6716 | Bourne shell. | |
6717 | @end table | |
ccc6cda3 | 6718 | |
28ef6c31 | 6719 | There are several @option{--enable-} options that alter how Bash is |
bb70624e | 6720 | compiled and linked, rather than changing run-time features. |
ccc6cda3 JA |
6721 | |
6722 | @table @code | |
f73dda09 JA |
6723 | @item --enable-largefile |
6724 | Enable support for @uref{http://www.sas.com/standards/large_file/x_open.20Mar96.html, | |
6725 | large files} if the operating system requires special compiler options | |
7117c2d2 JA |
6726 | to build programs which can access large files. This is enabled by |
6727 | default, if the operating system provides large file support. | |
f73dda09 | 6728 | |
bb70624e JA |
6729 | @item --enable-profiling |
6730 | This builds a Bash binary that produces profiling information to be | |
6731 | processed by @code{gprof} each time it is executed. | |
ccc6cda3 | 6732 | |
bb70624e JA |
6733 | @item --enable-static-link |
6734 | This causes Bash to be linked statically, if @code{gcc} is being used. | |
6735 | This could be used to build a version to use as root's shell. | |
6736 | @end table | |
6737 | ||
6738 | The @samp{minimal-config} option can be used to disable all of | |
6739 | the following options, but it is processed first, so individual | |
6740 | options may be enabled using @samp{enable-@var{feature}}. | |
6741 | ||
6742 | All of the following options except for @samp{disabled-builtins} and | |
6743 | @samp{xpg-echo-default} are | |
6744 | enabled by default, unless the operating system does not provide the | |
6745 | necessary support. | |
6746 | ||
6747 | @table @code | |
6748 | @item --enable-alias | |
6749 | Allow alias expansion and include the @code{alias} and @code{unalias} | |
6750 | builtins (@pxref{Aliases}). | |
ccc6cda3 | 6751 | |
bb70624e JA |
6752 | @item --enable-arith-for-command |
6753 | Include support for the alternate form of the @code{for} command | |
6754 | that behaves like the C language @code{for} statement | |
6755 | (@pxref{Looping Constructs}). | |
ccc6cda3 | 6756 | |
bb70624e JA |
6757 | @item --enable-array-variables |
6758 | Include support for one-dimensional array shell variables | |
6759 | (@pxref{Arrays}). | |
ccc6cda3 | 6760 | |
bb70624e JA |
6761 | @item --enable-bang-history |
6762 | Include support for @code{csh}-like history substitution | |
6763 | (@pxref{History Interaction}). | |
ccc6cda3 | 6764 | |
bb70624e JA |
6765 | @item --enable-brace-expansion |
6766 | Include @code{csh}-like brace expansion | |
6767 | ( @code{b@{a,b@}c} @expansion{} @code{bac bbc} ). | |
6768 | See @ref{Brace Expansion}, for a complete description. | |
ccc6cda3 | 6769 | |
bb70624e JA |
6770 | @item --enable-command-timing |
6771 | Include support for recognizing @code{time} as a reserved word and for | |
6772 | displaying timing statistics for the pipeline following @code{time} | |
6773 | (@pxref{Pipelines}). | |
6774 | This allows pipelines as well as shell builtins and functions to be timed. | |
ccc6cda3 | 6775 | |
bb70624e | 6776 | @item --enable-cond-command |
b80f6443 JA |
6777 | Include support for the @code{[[} conditional command. |
6778 | (@pxref{Conditional Constructs}). | |
6779 | ||
6780 | @item --enable-cond-regexp | |
6781 | Include support for matching POSIX regular expressions using the | |
6782 | @samp{=~} binary operator in the @code{[[} conditional command. | |
bb70624e | 6783 | (@pxref{Conditional Constructs}). |
ccc6cda3 | 6784 | |
95732b49 JA |
6785 | @item --enable-debugger |
6786 | Include support for the bash debugger (distributed separately). | |
6787 | ||
bb70624e JA |
6788 | @item --enable-directory-stack |
6789 | Include support for a @code{csh}-like directory stack and the | |
6790 | @code{pushd}, @code{popd}, and @code{dirs} builtins | |
6791 | (@pxref{The Directory Stack}). | |
ccc6cda3 | 6792 | |
bb70624e JA |
6793 | @item --enable-disabled-builtins |
6794 | Allow builtin commands to be invoked via @samp{builtin xxx} | |
6795 | even after @code{xxx} has been disabled using @samp{enable -n xxx}. | |
6796 | See @ref{Bash Builtins}, for details of the @code{builtin} and | |
6797 | @code{enable} builtin commands. | |
ccc6cda3 | 6798 | |
bb70624e JA |
6799 | @item --enable-dparen-arithmetic |
6800 | Include support for the @code{((@dots{}))} command | |
6801 | (@pxref{Conditional Constructs}). | |
ccc6cda3 | 6802 | |
bb70624e JA |
6803 | @item --enable-extended-glob |
6804 | Include support for the extended pattern matching features described | |
6805 | above under @ref{Pattern Matching}. | |
ccc6cda3 | 6806 | |
bb70624e JA |
6807 | @item --enable-help-builtin |
6808 | Include the @code{help} builtin, which displays help on shell builtins and | |
6809 | variables (@pxref{Bash Builtins}). | |
ccc6cda3 | 6810 | |
bb70624e JA |
6811 | @item --enable-history |
6812 | Include command history and the @code{fc} and @code{history} | |
6813 | builtin commands (@pxref{Bash History Facilities}). | |
ccc6cda3 | 6814 | |
bb70624e JA |
6815 | @item --enable-job-control |
6816 | This enables the job control features (@pxref{Job Control}), | |
6817 | if the operating system supports them. | |
ccc6cda3 | 6818 | |
b80f6443 JA |
6819 | @item --enable-multibyte |
6820 | This enables support for multibyte characters if the operating | |
6821 | system provides the necessary support. | |
6822 | ||
bb70624e JA |
6823 | @item --enable-net-redirections |
6824 | This enables the special handling of filenames of the form | |
6825 | @code{/dev/tcp/@var{host}/@var{port}} and | |
6826 | @code{/dev/udp/@var{host}/@var{port}} | |
6827 | when used in redirections (@pxref{Redirections}). | |
ccc6cda3 | 6828 | |
bb70624e JA |
6829 | @item --enable-process-substitution |
6830 | This enables process substitution (@pxref{Process Substitution}) if | |
6831 | the operating system provides the necessary support. | |
ccc6cda3 | 6832 | |
95732b49 JA |
6833 | @item --enable-progcomp |
6834 | Enable the programmable completion facilities | |
6835 | (@pxref{Programmable Completion}). | |
6836 | If Readline is not enabled, this option has no effect. | |
6837 | ||
bb70624e JA |
6838 | @item --enable-prompt-string-decoding |
6839 | Turn on the interpretation of a number of backslash-escaped characters | |
28ef6c31 | 6840 | in the @env{$PS1}, @env{$PS2}, @env{$PS3}, and @env{$PS4} prompt |
bb70624e JA |
6841 | strings. See @ref{Printing a Prompt}, for a complete list of prompt |
6842 | string escape sequences. | |
ccc6cda3 | 6843 | |
bb70624e JA |
6844 | @item --enable-readline |
6845 | Include support for command-line editing and history with the Bash | |
6846 | version of the Readline library (@pxref{Command Line Editing}). | |
ccc6cda3 | 6847 | |
bb70624e JA |
6848 | @item --enable-restricted |
6849 | Include support for a @dfn{restricted shell}. If this is enabled, Bash, | |
6850 | when called as @code{rbash}, enters a restricted mode. See | |
6851 | @ref{The Restricted Shell}, for a description of restricted mode. | |
ccc6cda3 | 6852 | |
bb70624e JA |
6853 | @item --enable-select |
6854 | Include the @code{select} builtin, which allows the generation of simple | |
6855 | menus (@pxref{Conditional Constructs}). | |
ccc6cda3 | 6856 | |
95732b49 JA |
6857 | @item --enable-separate-helpfiles |
6858 | Use external files for the documentation displayed by the @code{help} builtin | |
6859 | instead of storing the text internally. | |
6860 | ||
6861 | @item --enable-single-help-strings | |
6862 | Store the text displayed by the @code{help} builtin as a single string for | |
6863 | each help topic. This aids in translating the text to different languages. | |
6864 | You may need to disable this if your compiler cannot handle very long string | |
6865 | literals. | |
6866 | ||
6867 | @item --enable-strict-posix-default | |
6868 | Make Bash @sc{posix}-conformant by default (@pxref{Bash POSIX Mode}). | |
6869 | ||
bb70624e JA |
6870 | @item --enable-usg-echo-default |
6871 | A synonym for @code{--enable-xpg-echo-default}. | |
ccc6cda3 | 6872 | |
bb70624e JA |
6873 | @item --enable-xpg-echo-default |
6874 | Make the @code{echo} builtin expand backslash-escaped characters by default, | |
28ef6c31 | 6875 | without requiring the @option{-e} option. |
bb70624e JA |
6876 | This sets the default value of the @code{xpg_echo} shell option to @code{on}, |
6877 | which makes the Bash @code{echo} behave more like the version specified in | |
95732b49 | 6878 | the Single Unix Specification, version 3. |
bb70624e JA |
6879 | @xref{Bash Builtins}, for a description of the escape sequences that |
6880 | @code{echo} recognizes. | |
ccc6cda3 | 6881 | |
bb70624e | 6882 | @end table |
ccc6cda3 | 6883 | |
bb70624e JA |
6884 | The file @file{config-top.h} contains C Preprocessor |
6885 | @samp{#define} statements for options which are not settable from | |
6886 | @code{configure}. | |
6887 | Some of these are not meant to be changed; beware of the consequences if | |
6888 | you do. | |
6889 | Read the comments associated with each definition for more | |
6890 | information about its effect. | |
ccc6cda3 | 6891 | |
bb70624e JA |
6892 | @node Reporting Bugs |
6893 | @appendix Reporting Bugs | |
ccc6cda3 | 6894 | |
bb70624e JA |
6895 | Please report all bugs you find in Bash. |
6896 | But first, you should | |
6897 | make sure that it really is a bug, and that it appears in the latest | |
b80f6443 JA |
6898 | version of Bash. |
6899 | The latest version of Bash is always available for FTP from | |
6900 | @uref{ftp://ftp.gnu.org/pub/bash/}. | |
ccc6cda3 | 6901 | |
bb70624e JA |
6902 | Once you have determined that a bug actually exists, use the |
6903 | @code{bashbug} command to submit a bug report. | |
6904 | If you have a fix, you are encouraged to mail that as well! | |
6905 | Suggestions and `philosophical' bug reports may be mailed | |
6906 | to @email{bug-bash@@gnu.org} or posted to the Usenet | |
6907 | newsgroup @code{gnu.bash.bug}. | |
ccc6cda3 | 6908 | |
bb70624e JA |
6909 | All bug reports should include: |
6910 | @itemize @bullet | |
6911 | @item | |
6912 | The version number of Bash. | |
6913 | @item | |
6914 | The hardware and operating system. | |
6915 | @item | |
6916 | The compiler used to compile Bash. | |
6917 | @item | |
6918 | A description of the bug behaviour. | |
6919 | @item | |
6920 | A short script or `recipe' which exercises the bug and may be used | |
6921 | to reproduce it. | |
6922 | @end itemize | |
ccc6cda3 | 6923 | |
bb70624e JA |
6924 | @noindent |
6925 | @code{bashbug} inserts the first three items automatically into | |
6926 | the template it provides for filing a bug report. | |
ccc6cda3 | 6927 | |
bb70624e JA |
6928 | Please send all reports concerning this manual to |
6929 | @email{chet@@po.CWRU.Edu}. | |
ccc6cda3 | 6930 | |
bb70624e JA |
6931 | @node Major Differences From The Bourne Shell |
6932 | @appendix Major Differences From The Bourne Shell | |
d166f048 | 6933 | |
bb70624e JA |
6934 | Bash implements essentially the same grammar, parameter and |
6935 | variable expansion, redirection, and quoting as the Bourne Shell. | |
0628567a | 6936 | Bash uses the @sc{posix} standard as the specification of |
bb70624e JA |
6937 | how these features are to be implemented. There are some |
6938 | differences between the traditional Bourne shell and Bash; this | |
6939 | section quickly details the differences of significance. A | |
6940 | number of these differences are explained in greater depth in | |
6941 | previous sections. | |
95732b49 JA |
6942 | This section uses the version of @code{sh} included in SVR4.2 (the |
6943 | last version of the historical Bourne shell) as the baseline reference. | |
ccc6cda3 | 6944 | |
bb70624e | 6945 | @itemize @bullet |
ccc6cda3 | 6946 | |
ccc6cda3 | 6947 | @item |
bb70624e | 6948 | Bash is @sc{posix}-conformant, even where the @sc{posix} specification |
28ef6c31 | 6949 | differs from traditional @code{sh} behavior (@pxref{Bash POSIX Mode}). |
ccc6cda3 JA |
6950 | |
6951 | @item | |
bb70624e | 6952 | Bash has multi-character invocation options (@pxref{Invoking Bash}). |
ccc6cda3 JA |
6953 | |
6954 | @item | |
bb70624e JA |
6955 | Bash has command-line editing (@pxref{Command Line Editing}) and |
6956 | the @code{bind} builtin. | |
ccc6cda3 JA |
6957 | |
6958 | @item | |
bb70624e JA |
6959 | Bash provides a programmable word completion mechanism |
6960 | (@pxref{Programmable Completion}), and two builtin commands, | |
6961 | @code{complete} and @code{compgen}, to manipulate it. | |
ccc6cda3 | 6962 | |
bb70624e JA |
6963 | @item |
6964 | Bash has command history (@pxref{Bash History Facilities}) and the | |
6965 | @code{history} and @code{fc} builtins to manipulate it. | |
b80f6443 JA |
6966 | The Bash history list maintains timestamp information and uses the |
6967 | value of the @code{HISTTIMEFORMAT} variable to display it. | |
ccc6cda3 | 6968 | |
bb70624e JA |
6969 | @item |
6970 | Bash implements @code{csh}-like history expansion | |
6971 | (@pxref{History Interaction}). | |
ccc6cda3 | 6972 | |
bb70624e JA |
6973 | @item |
6974 | Bash has one-dimensional array variables (@pxref{Arrays}), and the | |
6975 | appropriate variable expansions and assignment syntax to use them. | |
6976 | Several of the Bash builtins take options to act on arrays. | |
6977 | Bash provides a number of built-in array variables. | |
ccc6cda3 | 6978 | |
bb70624e JA |
6979 | @item |
6980 | The @code{$'@dots{}'} quoting syntax, which expands ANSI-C | |
6981 | backslash-escaped characters in the text between the single quotes, | |
6982 | is supported (@pxref{ANSI-C Quoting}). | |
ccc6cda3 | 6983 | |
bb70624e JA |
6984 | @item |
6985 | Bash supports the @code{$"@dots{}"} quoting syntax to do | |
6986 | locale-specific translation of the characters between the double | |
28ef6c31 | 6987 | quotes. The @option{-D}, @option{--dump-strings}, and @option{--dump-po-strings} |
bb70624e JA |
6988 | invocation options list the translatable strings found in a script |
6989 | (@pxref{Locale Translation}). | |
ccc6cda3 | 6990 | |
bb70624e JA |
6991 | @item |
6992 | Bash implements the @code{!} keyword to negate the return value of | |
6993 | a pipeline (@pxref{Pipelines}). | |
6994 | Very useful when an @code{if} statement needs to act only if a test fails. | |
95732b49 JA |
6995 | The Bash @samp{-o pipefail} option to @code{set} will cause a pipeline to |
6996 | return a failure status if any command fails. | |
ccc6cda3 | 6997 | |
bb70624e JA |
6998 | @item |
6999 | Bash has the @code{time} reserved word and command timing (@pxref{Pipelines}). | |
7000 | The display of the timing statistics may be controlled with the | |
28ef6c31 | 7001 | @env{TIMEFORMAT} variable. |
ccc6cda3 | 7002 | |
bb70624e JA |
7003 | @item |
7004 | Bash implements the @code{for (( @var{expr1} ; @var{expr2} ; @var{expr3} ))} | |
7005 | arithmetic for command, similar to the C language (@pxref{Looping Constructs}). | |
ccc6cda3 | 7006 | |
bb70624e JA |
7007 | @item |
7008 | Bash includes the @code{select} compound command, which allows the | |
7009 | generation of simple menus (@pxref{Conditional Constructs}). | |
ccc6cda3 | 7010 | |
bb70624e JA |
7011 | @item |
7012 | Bash includes the @code{[[} compound command, which makes conditional | |
95732b49 JA |
7013 | testing part of the shell grammar (@pxref{Conditional Constructs}), including |
7014 | optional regular expression matching. | |
7015 | ||
7016 | @item | |
7017 | Bash provides optional case-insensitive matching for the @code{case} and | |
7018 | @code{[[} constructs. | |
ccc6cda3 | 7019 | |
bb70624e JA |
7020 | @item |
7021 | Bash includes brace expansion (@pxref{Brace Expansion}) and tilde | |
7022 | expansion (@pxref{Tilde Expansion}). | |
ccc6cda3 | 7023 | |
bb70624e JA |
7024 | @item |
7025 | Bash implements command aliases and the @code{alias} and @code{unalias} | |
7026 | builtins (@pxref{Aliases}). | |
ccc6cda3 | 7027 | |
bb70624e JA |
7028 | @item |
7029 | Bash provides shell arithmetic, the @code{((} compound command | |
7030 | (@pxref{Conditional Constructs}), | |
7031 | and arithmetic expansion (@pxref{Shell Arithmetic}). | |
ccc6cda3 | 7032 | |
bb70624e JA |
7033 | @item |
7034 | Variables present in the shell's initial environment are automatically | |
7035 | exported to child processes. The Bourne shell does not normally do | |
7036 | this unless the variables are explicitly marked using the @code{export} | |
7037 | command. | |
ccc6cda3 | 7038 | |
95732b49 JA |
7039 | @item |
7040 | Bash supports the @samp{+=} assignment operator, which appends to the value | |
7041 | of the variable named on the left hand side. | |
7042 | ||
bb70624e JA |
7043 | @item |
7044 | Bash includes the @sc{posix} pattern removal @samp{%}, @samp{#}, @samp{%%} | |
7045 | and @samp{##} expansions to remove leading or trailing substrings from | |
7046 | variable values (@pxref{Shell Parameter Expansion}). | |
ccc6cda3 | 7047 | |
bb70624e JA |
7048 | @item |
7049 | The expansion @code{$@{#xx@}}, which returns the length of @code{$@{xx@}}, | |
7050 | is supported (@pxref{Shell Parameter Expansion}). | |
ccc6cda3 | 7051 | |
bb70624e JA |
7052 | @item |
7053 | The expansion @code{$@{var:}@var{offset}@code{[:}@var{length}@code{]@}}, | |
7054 | which expands to the substring of @code{var}'s value of length | |
7055 | @var{length}, beginning at @var{offset}, is present | |
7056 | (@pxref{Shell Parameter Expansion}). | |
ccc6cda3 | 7057 | |
bb70624e JA |
7058 | @item |
7059 | The expansion | |
7060 | @code{$@{var/[/]}@var{pattern}@code{[/}@var{replacement}@code{]@}}, | |
7061 | which matches @var{pattern} and replaces it with @var{replacement} in | |
7062 | the value of @code{var}, is available (@pxref{Shell Parameter Expansion}). | |
ccc6cda3 | 7063 | |
bb70624e JA |
7064 | @item |
7065 | The expansion @code{$@{!@var{prefix@}*}} expansion, which expands to | |
7066 | the names of all shell variables whose names begin with @var{prefix}, | |
7067 | is available (@pxref{Shell Parameter Expansion}). | |
ccc6cda3 | 7068 | |
bb70624e JA |
7069 | @item |
7070 | Bash has @var{indirect} variable expansion using @code{$@{!word@}} | |
7071 | (@pxref{Shell Parameter Expansion}). | |
ccc6cda3 | 7072 | |
bb70624e JA |
7073 | @item |
7074 | Bash can expand positional parameters beyond @code{$9} using | |
7075 | @code{$@{@var{num}@}}. | |
ccc6cda3 | 7076 | |
bb70624e JA |
7077 | @item |
7078 | The @sc{posix} @code{$()} form of command substitution | |
7079 | is implemented (@pxref{Command Substitution}), | |
7080 | and preferred to the Bourne shell's @code{``} (which | |
7081 | is also implemented for backwards compatibility). | |
ccc6cda3 | 7082 | |
bb70624e JA |
7083 | @item |
7084 | Bash has process substitution (@pxref{Process Substitution}). | |
ccc6cda3 | 7085 | |
bb70624e JA |
7086 | @item |
7087 | Bash automatically assigns variables that provide information about the | |
28ef6c31 JA |
7088 | current user (@env{UID}, @env{EUID}, and @env{GROUPS}), the current host |
7089 | (@env{HOSTTYPE}, @env{OSTYPE}, @env{MACHTYPE}, and @env{HOSTNAME}), | |
7090 | and the instance of Bash that is running (@env{BASH}, | |
7091 | @env{BASH_VERSION}, and @env{BASH_VERSINFO}). @xref{Bash Variables}, | |
bb70624e | 7092 | for details. |
ccc6cda3 | 7093 | |
bb70624e | 7094 | @item |
28ef6c31 | 7095 | The @env{IFS} variable is used to split only the results of expansion, |
bb70624e JA |
7096 | not all words (@pxref{Word Splitting}). |
7097 | This closes a longstanding shell security hole. | |
ccc6cda3 | 7098 | |
bb70624e | 7099 | @item |
0628567a | 7100 | Bash implements the full set of @sc{posix} filename expansion operators, |
bb70624e JA |
7101 | including @var{character classes}, @var{equivalence classes}, and |
7102 | @var{collating symbols} (@pxref{Filename Expansion}). | |
ccc6cda3 | 7103 | |
bb70624e JA |
7104 | @item |
7105 | Bash implements extended pattern matching features when the @code{extglob} | |
7106 | shell option is enabled (@pxref{Pattern Matching}). | |
ccc6cda3 | 7107 | |
bb70624e JA |
7108 | @item |
7109 | It is possible to have a variable and a function with the same name; | |
7110 | @code{sh} does not separate the two name spaces. | |
ccc6cda3 | 7111 | |
bb70624e JA |
7112 | @item |
7113 | Bash functions are permitted to have local variables using the | |
7114 | @code{local} builtin, and thus useful recursive functions may be written | |
7115 | (@pxref{Bash Builtins}). | |
ccc6cda3 | 7116 | |
bb70624e JA |
7117 | @item |
7118 | Variable assignments preceding commands affect only that command, even | |
7119 | builtins and functions (@pxref{Environment}). | |
7120 | In @code{sh}, all variable assignments | |
7121 | preceding commands are global unless the command is executed from the | |
7122 | file system. | |
ccc6cda3 | 7123 | |
bb70624e JA |
7124 | @item |
7125 | Bash performs filename expansion on filenames specified as operands | |
7126 | to input and output redirection operators (@pxref{Redirections}). | |
ccc6cda3 | 7127 | |
bb70624e JA |
7128 | @item |
7129 | Bash contains the @samp{<>} redirection operator, allowing a file to be | |
7130 | opened for both reading and writing, and the @samp{&>} redirection | |
7131 | operator, for directing standard output and standard error to the same | |
7132 | file (@pxref{Redirections}). | |
ccc6cda3 | 7133 | |
95732b49 JA |
7134 | @item |
7135 | Bash includes the @samp{<<<} redirection operator, allowing a string to | |
7136 | be used as the standard input to a command. | |
7137 | ||
7138 | @item | |
7139 | Bash implements the @samp{[n]<&@var{word}} and @samp{[n]>&@var{word}} | |
7140 | redirection operators, which move one file descriptor to another. | |
7141 | ||
bb70624e JA |
7142 | @item |
7143 | Bash treats a number of filenames specially when they are | |
7144 | used in redirection operators (@pxref{Redirections}). | |
ccc6cda3 | 7145 | |
bb70624e JA |
7146 | @item |
7147 | Bash can open network connections to arbitrary machines and services | |
7148 | with the redirection operators (@pxref{Redirections}). | |
ccc6cda3 | 7149 | |
bb70624e JA |
7150 | @item |
7151 | The @code{noclobber} option is available to avoid overwriting existing | |
7152 | files with output redirection (@pxref{The Set Builtin}). | |
7153 | The @samp{>|} redirection operator may be used to override @code{noclobber}. | |
d166f048 | 7154 | |
bb70624e JA |
7155 | @item |
7156 | The Bash @code{cd} and @code{pwd} builtins (@pxref{Bourne Shell Builtins}) | |
28ef6c31 | 7157 | each take @option{-L} and @option{-P} options to switch between logical and |
bb70624e | 7158 | physical modes. |
d166f048 | 7159 | |
bb70624e JA |
7160 | @item |
7161 | Bash allows a function to override a builtin with the same name, and provides | |
7162 | access to that builtin's functionality within the function via the | |
7163 | @code{builtin} and @code{command} builtins (@pxref{Bash Builtins}). | |
d166f048 | 7164 | |
bb70624e JA |
7165 | @item |
7166 | The @code{command} builtin allows selective disabling of functions | |
7167 | when command lookup is performed (@pxref{Bash Builtins}). | |
ccc6cda3 | 7168 | |
bb70624e JA |
7169 | @item |
7170 | Individual builtins may be enabled or disabled using the @code{enable} | |
7171 | builtin (@pxref{Bash Builtins}). | |
b72432fd | 7172 | |
bb70624e JA |
7173 | @item |
7174 | The Bash @code{exec} builtin takes additional options that allow users | |
7175 | to control the contents of the environment passed to the executed | |
7176 | command, and what the zeroth argument to the command is to be | |
7177 | (@pxref{Bourne Shell Builtins}). | |
ccc6cda3 | 7178 | |
bb70624e JA |
7179 | @item |
7180 | Shell functions may be exported to children via the environment | |
7181 | using @code{export -f} (@pxref{Shell Functions}). | |
ccc6cda3 | 7182 | |
bb70624e JA |
7183 | @item |
7184 | The Bash @code{export}, @code{readonly}, and @code{declare} builtins can | |
28ef6c31 | 7185 | take a @option{-f} option to act on shell functions, a @option{-p} option to |
bb70624e | 7186 | display variables with various attributes set in a format that can be |
28ef6c31 | 7187 | used as shell input, a @option{-n} option to remove various variable |
bb70624e JA |
7188 | attributes, and @samp{name=value} arguments to set variable attributes |
7189 | and values simultaneously. | |
cce855bc | 7190 | |
bb70624e JA |
7191 | @item |
7192 | The Bash @code{hash} builtin allows a name to be associated with | |
7193 | an arbitrary filename, even when that filename cannot be found by | |
28ef6c31 | 7194 | searching the @env{$PATH}, using @samp{hash -p} |
bb70624e | 7195 | (@pxref{Bourne Shell Builtins}). |
cce855bc | 7196 | |
bb70624e JA |
7197 | @item |
7198 | Bash includes a @code{help} builtin for quick reference to shell | |
7199 | facilities (@pxref{Bash Builtins}). | |
cce855bc | 7200 | |
bb70624e JA |
7201 | @item |
7202 | The @code{printf} builtin is available to display formatted output | |
7203 | (@pxref{Bash Builtins}). | |
ccc6cda3 | 7204 | |
bb70624e JA |
7205 | @item |
7206 | The Bash @code{read} builtin (@pxref{Bash Builtins}) | |
7207 | will read a line ending in @samp{\} with | |
28ef6c31 | 7208 | the @option{-r} option, and will use the @env{REPLY} variable as a |
bb70624e JA |
7209 | default if no non-option arguments are supplied. |
7210 | The Bash @code{read} builtin | |
28ef6c31 JA |
7211 | also accepts a prompt string with the @option{-p} option and will use |
7212 | Readline to obtain the line when given the @option{-e} option. | |
bb70624e | 7213 | The @code{read} builtin also has additional options to control input: |
28ef6c31 JA |
7214 | the @option{-s} option will turn off echoing of input characters as |
7215 | they are read, the @option{-t} option will allow @code{read} to time out | |
bb70624e | 7216 | if input does not arrive within a specified number of seconds, the |
28ef6c31 JA |
7217 | @option{-n} option will allow reading only a specified number of |
7218 | characters rather than a full line, and the @option{-d} option will read | |
bb70624e | 7219 | until a particular character rather than newline. |
ccc6cda3 | 7220 | |
bb70624e JA |
7221 | @item |
7222 | The @code{return} builtin may be used to abort execution of scripts | |
7223 | executed with the @code{.} or @code{source} builtins | |
7224 | (@pxref{Bourne Shell Builtins}). | |
ccc6cda3 | 7225 | |
bb70624e JA |
7226 | @item |
7227 | Bash includes the @code{shopt} builtin, for finer control of shell | |
f73dda09 JA |
7228 | optional capabilities (@pxref{Bash Builtins}), and allows these options |
7229 | to be set and unset at shell invocation (@pxref{Invoking Bash}). | |
ccc6cda3 | 7230 | |
bb70624e JA |
7231 | @item |
7232 | Bash has much more optional behavior controllable with the @code{set} | |
7233 | builtin (@pxref{The Set Builtin}). | |
ccc6cda3 | 7234 | |
b80f6443 JA |
7235 | @item |
7236 | The @samp{-x} (@code{xtrace}) option displays commands other than | |
7237 | simple commands when performing an execution trace | |
7238 | (@pxref{The Set Builtin}). | |
7239 | ||
bb70624e JA |
7240 | @item |
7241 | The @code{test} builtin (@pxref{Bourne Shell Builtins}) | |
7242 | is slightly different, as it implements the @sc{posix} algorithm, | |
7243 | which specifies the behavior based on the number of arguments. | |
d166f048 | 7244 | |
b80f6443 JA |
7245 | @item |
7246 | Bash includes the @code{caller} builtin, which displays the context of | |
7247 | any active subroutine call (a shell function or a script executed with | |
7248 | the @code{.} or @code{source} builtins). This supports the bash | |
7249 | debugger. | |
7250 | ||
bb70624e | 7251 | @item |
f73dda09 JA |
7252 | The @code{trap} builtin (@pxref{Bourne Shell Builtins}) allows a |
7253 | @code{DEBUG} pseudo-signal specification, similar to @code{EXIT}. | |
b80f6443 JA |
7254 | Commands specified with a @code{DEBUG} trap are executed before every |
7255 | simple command, @code{for} command, @code{case} command, | |
7256 | @code{select} command, every arithmetic @code{for} command, and before | |
7257 | the first command executes in a shell function. | |
7117c2d2 | 7258 | The @code{DEBUG} trap is not inherited by shell functions unless the |
b80f6443 JA |
7259 | function has been given the @code{trace} attribute or the |
7260 | @code{functrace} option has been enabled using the @code{shopt} builtin. | |
7261 | The @code{extdebug} shell option has additional effects on the | |
7262 | @code{DEBUG} trap. | |
f73dda09 JA |
7263 | |
7264 | The @code{trap} builtin (@pxref{Bourne Shell Builtins}) allows an | |
7265 | @code{ERR} pseudo-signal specification, similar to @code{EXIT} and @code{DEBUG}. | |
7266 | Commands specified with an @code{ERR} trap are executed after a simple | |
7267 | command fails, with a few exceptions. | |
b80f6443 JA |
7268 | The @code{ERR} trap is not inherited by shell functions unless the |
7269 | @code{-o errtrace} option to the @code{set} builtin is enabled. | |
7270 | ||
7271 | The @code{trap} builtin (@pxref{Bourne Shell Builtins}) allows a | |
7272 | @code{RETURN} pseudo-signal specification, similar to | |
7273 | @code{EXIT} and @code{DEBUG}. | |
7274 | Commands specified with an @code{RETURN} trap are executed before | |
7275 | execution resumes after a shell function or a shell script executed with | |
7276 | @code{.} or @code{source} returns. | |
95732b49 JA |
7277 | The @code{RETURN} trap is not inherited by shell functions unless the |
7278 | function has been given the @code{trace} attribute or the | |
7279 | @code{functrace} option has been enabled using the @code{shopt} builtin. | |
d166f048 | 7280 | |
bb70624e JA |
7281 | @item |
7282 | The Bash @code{type} builtin is more extensive and gives more information | |
7283 | about the names it finds (@pxref{Bash Builtins}). | |
cce855bc | 7284 | |
bb70624e | 7285 | @item |
28ef6c31 | 7286 | The Bash @code{umask} builtin permits a @option{-p} option to cause |
bb70624e JA |
7287 | the output to be displayed in the form of a @code{umask} command |
7288 | that may be reused as input (@pxref{Bourne Shell Builtins}). | |
ccc6cda3 | 7289 | |
bb70624e JA |
7290 | @item |
7291 | Bash implements a @code{csh}-like directory stack, and provides the | |
7292 | @code{pushd}, @code{popd}, and @code{dirs} builtins to manipulate it | |
7293 | (@pxref{The Directory Stack}). | |
7294 | Bash also makes the directory stack visible as the value of the | |
28ef6c31 | 7295 | @env{DIRSTACK} shell variable. |
d166f048 | 7296 | |
bb70624e JA |
7297 | @item |
7298 | Bash interprets special backslash-escaped characters in the prompt | |
7299 | strings when interactive (@pxref{Printing a Prompt}). | |
cce855bc | 7300 | |
bb70624e JA |
7301 | @item |
7302 | The Bash restricted mode is more useful (@pxref{The Restricted Shell}); | |
7303 | the SVR4.2 shell restricted mode is too limited. | |
d166f048 | 7304 | |
bb70624e JA |
7305 | @item |
7306 | The @code{disown} builtin can remove a job from the internal shell | |
7307 | job table (@pxref{Job Control Builtins}) or suppress the sending | |
7308 | of @code{SIGHUP} to a job when the shell exits as the result of a | |
7309 | @code{SIGHUP}. | |
d166f048 | 7310 | |
95732b49 JA |
7311 | @item |
7312 | Bash includes a number of features to support a separate debugger for | |
7313 | shell scripts. | |
7314 | ||
bb70624e JA |
7315 | @item |
7316 | The SVR4.2 shell has two privilege-related builtins | |
7317 | (@code{mldmode} and @code{priv}) not present in Bash. | |
d166f048 | 7318 | |
bb70624e JA |
7319 | @item |
7320 | Bash does not have the @code{stop} or @code{newgrp} builtins. | |
ccc6cda3 | 7321 | |
bb70624e | 7322 | @item |
28ef6c31 | 7323 | Bash does not use the @env{SHACCT} variable or perform shell accounting. |
ccc6cda3 | 7324 | |
bb70624e | 7325 | @item |
28ef6c31 JA |
7326 | The SVR4.2 @code{sh} uses a @env{TIMEOUT} variable like Bash uses |
7327 | @env{TMOUT}. | |
ccc6cda3 | 7328 | |
bb70624e | 7329 | @end itemize |
d166f048 | 7330 | |
bb70624e JA |
7331 | @noindent |
7332 | More features unique to Bash may be found in @ref{Bash Features}. | |
d166f048 | 7333 | |
ccc6cda3 | 7334 | |
bb70624e | 7335 | @appendixsec Implementation Differences From The SVR4.2 Shell |
ccc6cda3 | 7336 | |
bb70624e JA |
7337 | Since Bash is a completely new implementation, it does not suffer from |
7338 | many of the limitations of the SVR4.2 shell. For instance: | |
ccc6cda3 | 7339 | |
bb70624e | 7340 | @itemize @bullet |
ccc6cda3 | 7341 | |
bb70624e JA |
7342 | @item |
7343 | Bash does not fork a subshell when redirecting into or out of | |
7344 | a shell control structure such as an @code{if} or @code{while} | |
7345 | statement. | |
ccc6cda3 | 7346 | |
bb70624e JA |
7347 | @item |
7348 | Bash does not allow unbalanced quotes. The SVR4.2 shell will silently | |
7349 | insert a needed closing quote at @code{EOF} under certain circumstances. | |
7350 | This can be the cause of some hard-to-find errors. | |
ccc6cda3 | 7351 | |
bb70624e JA |
7352 | @item |
7353 | The SVR4.2 shell uses a baroque memory management scheme based on | |
7354 | trapping @code{SIGSEGV}. If the shell is started from a process with | |
7355 | @code{SIGSEGV} blocked (e.g., by using the @code{system()} C library | |
7356 | function call), it misbehaves badly. | |
ccc6cda3 | 7357 | |
ccc6cda3 | 7358 | @item |
bb70624e | 7359 | In a questionable attempt at security, the SVR4.2 shell, |
28ef6c31 | 7360 | when invoked without the @option{-p} option, will alter its real |
bb70624e JA |
7361 | and effective @sc{uid} and @sc{gid} if they are less than some |
7362 | magic threshold value, commonly 100. | |
7363 | This can lead to unexpected results. | |
7364 | ||
ccc6cda3 | 7365 | @item |
bb70624e JA |
7366 | The SVR4.2 shell does not allow users to trap @code{SIGSEGV}, |
7367 | @code{SIGALRM}, or @code{SIGCHLD}. | |
7368 | ||
ccc6cda3 | 7369 | @item |
28ef6c31 JA |
7370 | The SVR4.2 shell does not allow the @env{IFS}, @env{MAILCHECK}, |
7371 | @env{PATH}, @env{PS1}, or @env{PS2} variables to be unset. | |
bb70624e | 7372 | |
ccc6cda3 | 7373 | @item |
bb70624e JA |
7374 | The SVR4.2 shell treats @samp{^} as the undocumented equivalent of |
7375 | @samp{|}. | |
7376 | ||
ccc6cda3 | 7377 | @item |
bb70624e JA |
7378 | Bash allows multiple option arguments when it is invoked (@code{-x -v}); |
7379 | the SVR4.2 shell allows only one option argument (@code{-xv}). In | |
7380 | fact, some versions of the shell dump core if the second argument begins | |
7381 | with a @samp{-}. | |
ccc6cda3 | 7382 | |
bb70624e JA |
7383 | @item |
7384 | The SVR4.2 shell exits a script if any builtin fails; Bash exits | |
0628567a JA |
7385 | a script only if one of the @sc{posix} special builtins fails, and |
7386 | only for certain failures, as enumerated in the @sc{posix} standard. | |
ccc6cda3 | 7387 | |
bb70624e JA |
7388 | @item |
7389 | The SVR4.2 shell behaves differently when invoked as @code{jsh} | |
7390 | (it turns on job control). | |
7391 | @end itemize | |
ccc6cda3 | 7392 | |
b80f6443 JA |
7393 | @node Copying This Manual |
7394 | @appendix Copying This Manual | |
7395 | ||
7396 | @menu | |
7397 | * GNU Free Documentation License:: License for copying this manual. | |
7398 | @end menu | |
7399 | ||
7400 | @include fdl.texi | |
7401 | ||
ccc6cda3 | 7402 | @node Builtin Index |
bb70624e | 7403 | @unnumbered Index of Shell Builtin Commands |
ccc6cda3 JA |
7404 | @printindex bt |
7405 | ||
7406 | @node Reserved Word Index | |
bb70624e | 7407 | @unnumbered Index of Shell Reserved Words |
ccc6cda3 JA |
7408 | @printindex rw |
7409 | ||
7410 | @node Variable Index | |
bb70624e | 7411 | @unnumbered Parameter and Variable Index |
ccc6cda3 JA |
7412 | @printindex vr |
7413 | ||
7414 | @node Function Index | |
bb70624e | 7415 | @unnumbered Function Index |
ccc6cda3 JA |
7416 | @printindex fn |
7417 | ||
7418 | @node Concept Index | |
bb70624e | 7419 | @unnumbered Concept Index |
ccc6cda3 JA |
7420 | @printindex cp |
7421 | ||
ccc6cda3 | 7422 | @bye |