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1 | This is the Bash FAQ, version 3.24, for Bash version 2.05b. |
2 | ||
3 | This document contains a set of frequently-asked questions concerning | |
4 | Bash, the GNU Bourne-Again Shell. Bash is a freely-available command | |
5 | interpreter with advanced features for both interactive use and shell | |
6 | programming. | |
7 | ||
8 | Another good source of basic information about shells is the collection | |
9 | of FAQ articles periodically posted to comp.unix.shell. | |
10 | ||
11 | Questions and comments concerning this document should be sent to | |
12 | chet@po.cwru.edu. | |
13 | ||
14 | This document is available for anonymous FTP with the URL | |
15 | ||
16 | ftp://ftp.cwru.edu/pub/bash/FAQ | |
17 | ||
18 | The Bash home page is http://cnswww.cns.cwru.edu/~chet/bash/bashtop.html | |
19 | ||
20 | ---------- | |
21 | Contents: | |
22 | ||
23 | Section A: The Basics | |
24 | ||
25 | A1) What is it? | |
26 | A2) What's the latest version? | |
27 | A3) Where can I get it? | |
28 | A4) On what machines will bash run? | |
29 | A5) Will bash run on operating systems other than Unix? | |
30 | A6) How can I build bash with gcc? | |
31 | A7) How can I make bash my login shell? | |
32 | A8) I just changed my login shell to bash, and now I can't FTP into my | |
33 | machine. Why not? | |
34 | A9) What's the `POSIX 1003.2 standard'? | |
35 | A10) What is the bash `posix mode'? | |
36 | ||
37 | Section B: The latest version | |
38 | ||
39 | B1) What's new in version 2.05b? | |
40 | B2) Are there any user-visible incompatibilities between bash-2.05b and | |
41 | bash-1.14.7? | |
42 | ||
43 | Section C: Differences from other Unix shells | |
44 | ||
45 | C1) How does bash differ from sh, the Bourne shell? | |
46 | C2) How does bash differ from the Korn shell, version ksh88? | |
47 | C3) Which new features in ksh-93 are not in bash, and which are? | |
48 | ||
49 | Section D: Why does bash do some things differently than other Unix shells? | |
50 | ||
51 | D1) Why does bash run a different version of `command' than | |
52 | `which command' says it will? | |
53 | D2) Why doesn't bash treat brace expansions exactly like csh? | |
54 | D3) Why doesn't bash have csh variable modifiers? | |
55 | D4) How can I make my csh aliases work when I convert to bash? | |
56 | D5) How can I pipe standard output and standard error from one command to | |
57 | another, like csh does with `|&'? | |
58 | D6) Now that I've converted from ksh to bash, are there equivalents to | |
59 | ksh features like autoloaded functions and the `whence' command? | |
60 | ||
61 | Section E: Why does bash do certain things the way it does? | |
62 | ||
63 | E1) Why is the bash builtin `test' slightly different from /bin/test? | |
64 | E2) Why does bash sometimes say `Broken pipe'? | |
65 | E3) When I have terminal escape sequences in my prompt, why does bash | |
66 | wrap lines at the wrong column? | |
67 | E4) If I pipe the output of a command into `read variable', why doesn't | |
68 | the output show up in $variable when the read command finishes? | |
69 | E5) I have a bunch of shell scripts that use backslash-escaped characters | |
70 | in arguments to `echo'. Bash doesn't interpret these characters. Why | |
71 | not, and how can I make it understand them? | |
72 | E6) Why doesn't a while or for loop get suspended when I type ^Z? | |
73 | E7) What about empty for loops in Makefiles? | |
74 | E8) Why does the arithmetic evaluation code complain about `08'? | |
75 | E9) Why does the pattern matching expression [A-Z]* match files beginning | |
76 | with every letter except `z'? | |
77 | E10) Why does `cd //' leave $PWD as `//'? | |
78 | E11) If I resize my xterm while another program is running, why doesn't bash | |
79 | notice the change? | |
80 | ||
81 | Section F: Things to watch out for on certain Unix versions | |
82 | ||
83 | F1) Why can't I use command line editing in my `cmdtool'? | |
84 | F2) I built bash on Solaris 2. Why do globbing expansions and filename | |
85 | completion chop off the first few characters of each filename? | |
86 | F3) Why does bash dump core after I interrupt username completion or | |
87 | `~user' tilde expansion on a machine running NIS? | |
88 | F4) I'm running SVR4.2. Why is the line erased every time I type `@'? | |
89 | F5) Why does bash report syntax errors when my C News scripts use a | |
90 | redirection before a subshell command? | |
91 | F6) Why can't I use vi-mode editing on Red Hat Linux 6.1? | |
92 | F7) Why do bash-2.05a and bash-2.05b fail to compile `printf.def' on | |
93 | HP/UX 11.x? | |
94 | ||
95 | Section G: How can I get bash to do certain common things? | |
96 | ||
97 | G1) How can I get bash to read and display eight-bit characters? | |
98 | G2) How do I write a function `x' to replace builtin command `x', but | |
99 | still invoke the command from within the function? | |
100 | G3) How can I find the value of a shell variable whose name is the value | |
101 | of another shell variable? | |
102 | G4) How can I make the bash `time' reserved word print timing output that | |
103 | looks like the output from my system's /usr/bin/time? | |
104 | G5) How do I get the current directory into my prompt? | |
105 | G6) How can I rename "*.foo" to "*.bar"? | |
106 | G7) How can I translate a filename from uppercase to lowercase? | |
107 | G8) How can I write a filename expansion (globbing) pattern that will match | |
108 | all files in the current directory except "." and ".."? | |
109 | ||
110 | Section H: Where do I go from here? | |
111 | ||
112 | H1) How do I report bugs in bash, and where should I look for fixes and | |
113 | advice? | |
114 | H2) What kind of bash documentation is there? | |
115 | H3) What's coming in future versions? | |
116 | H4) What's on the bash `wish list'? | |
117 | H5) When will the next release appear? | |
118 | ||
119 | ---------- | |
120 | Section A: The Basics | |
121 | ||
122 | A1) What is it? | |
123 | ||
124 | Bash is a Unix command interpreter (shell). It is an implementation of | |
125 | the Posix 1003.2 shell standard, and resembles the Korn and System V | |
126 | shells. | |
127 | ||
128 | Bash contains a number of enhancements over those shells, both | |
129 | for interactive use and shell programming. Features geared | |
130 | toward interactive use include command line editing, command | |
131 | history, job control, aliases, and prompt expansion. Programming | |
132 | features include additional variable expansions, shell | |
133 | arithmetic, and a number of variables and options to control | |
134 | shell behavior. | |
135 | ||
136 | Bash was originally written by Brian Fox of the Free Software | |
137 | Foundation. The current developer and maintainer is Chet Ramey | |
138 | of Case Western Reserve University. | |
139 | ||
140 | A2) What's the latest version? | |
141 | ||
142 | The latest version is 2.05b, first made available on Wednesday, 17 | |
143 | July, 2002. | |
144 | ||
145 | A3) Where can I get it? | |
146 | ||
147 | Bash is the GNU project's shell, and so is available from the | |
148 | master GNU archive site, ftp.gnu.org, and its mirrors. The | |
149 | latest version is also available for FTP from ftp.cwru.edu. | |
150 | The following URLs tell how to get version 2.05b: | |
151 | ||
152 | ftp://ftp.gnu.org/pub/gnu/bash/bash-2.05b.tar.gz | |
153 | ftp://ftp.cwru.edu/pub/bash/bash-2.05b.tar.gz | |
154 | ||
155 | Formatted versions of the documentation are available with the URLs: | |
156 | ||
157 | ftp://ftp.gnu.org/pub/gnu/bash/bash-doc-2.05b.tar.gz | |
158 | ftp://ftp.cwru.edu/pub/bash/bash-doc-2.05b.tar.gz | |
159 | ||
160 | A4) On what machines will bash run? | |
161 | ||
162 | Bash has been ported to nearly every version of UNIX. All you | |
163 | should have to do to build it on a machine for which a port | |
164 | exists is to type `configure' and then `make'. The build process | |
165 | will attempt to discover the version of UNIX you have and tailor | |
166 | itself accordingly, using a script created by GNU autoconf. | |
167 | ||
168 | More information appears in the file `INSTALL' in the distribution. | |
169 | ||
170 | The Bash web page (http://cnswww.cns.cwru.edu/~chet/bash/bashtop.html) | |
171 | explains how to obtain binary versions of bash for most of the major | |
172 | commercial Unix systems. | |
173 | ||
174 | A5) Will bash run on operating systems other than Unix? | |
175 | ||
176 | Configuration specifics for Unix-like systems such as QNX and | |
177 | LynxOS are included in the distribution. Bash-2.05 and later | |
178 | versions should compile and run on Minix 2.0 (patches were | |
179 | contributed), but I don't believe anyone has built bash-2.x on | |
180 | earlier Minix versions yet. | |
181 | ||
182 | Bash has been ported to versions of Windows implementing the Win32 | |
183 | programming interface. This includes Windows 95 and Windows NT. | |
184 | The port was done by Cygnus Solutions as part of their CYGWIN | |
185 | project. For more information about the project, look at the URLs | |
186 | ||
187 | http://www.cygwin.com/ | |
188 | http://sourceware.cygnus.com/cygwin | |
189 | ||
190 | Cygnus originally ported bash-1.14.7, and that port was part of their | |
191 | early GNU-Win32 (the original name) releases. Cygnus has also done a | |
192 | port of bash-2.05 to the CYGWIN environment, and it is available as | |
193 | part of their current release. | |
194 | ||
195 | Bash-2.05b should require no local Cygnus changes to build and run under | |
196 | CYGWIN. | |
197 | ||
198 | The Cygnus port works only on Intel machines. There is a port of bash | |
199 | (I don't know which version) to the alpha/NT environment available from | |
200 | ||
201 | ftp://ftp.gnustep.org//pub/win32/bash-alpha-nt-1.01.tar.gz | |
202 | ||
203 | DJ Delorie has a port of bash-2.x which runs under MS-DOS, as part | |
204 | of the DJGPP project. For more information on the project, see | |
205 | ||
206 | http://www.delorie.com/djgpp/ | |
207 | ||
208 | I have been told that the original DJGPP port was done by Daisuke Aoyama. | |
209 | ||
210 | Mark Elbrecht <snowball3@bigfoot.com> has sent me notice that bash-2.04 | |
211 | is available for DJGPP V2. The files are available as: | |
212 | ||
213 | ftp://ftp.simtel.net/pub/simtelnet/gnu/djgpp/v2gnu/bsh204b.zip binary | |
214 | ftp://ftp.simtel.net/pub/simtelnet/gnu/djgpp/v2gnu/bsh204d.zip documentation | |
215 | ftp://ftp.simtel.net/pub/simtelnet/gnu/djgpp/v2gnu/bsh204s.zip source | |
216 | ||
217 | Mark has begun to work with bash-2.05, but I don't know the status. | |
218 | ||
219 | Ports of bash-1.12 and bash-2.0 are available for OS/2 from | |
220 | ||
221 | ftp://hobbes.nmsu.edu/pub/os2/util/shell/bash_112.zip | |
222 | ftp://hobbes.nmsu.edu/pub/os2/util/shell/bash-2.0(253).zip | |
223 | ||
224 | I haven't looked at either, but the second appears to be a binary-only | |
225 | distribution. Beware. | |
226 | ||
227 | I have received word that Bash (I'm not sure which version, but I | |
228 | believe that it's at least bash-2.02.1) is the standard shell on | |
229 | BeOS. | |
230 | ||
231 | A6) How can I build bash with gcc? | |
232 | ||
233 | Bash configures to use gcc by default if it is available. Read the | |
234 | file INSTALL in the distribution for more information. | |
235 | ||
236 | A7) How can I make bash my login shell? | |
237 | ||
238 | Some machines let you use `chsh' to change your login shell. Other | |
239 | systems use `passwd -s' or `passwd -e'. If one of these works for | |
240 | you, that's all you need. Note that many systems require the full | |
241 | pathname to a shell to appear in /etc/shells before you can make it | |
242 | your login shell. For this, you may need the assistance of your | |
243 | friendly local system administrator. | |
244 | ||
245 | If you cannot do this, you can still use bash as your login shell, but | |
246 | you need to perform some tricks. The basic idea is to add a command | |
247 | to your login shell's startup file to replace your login shell with | |
248 | bash. | |
249 | ||
250 | For example, if your login shell is csh or tcsh, and you have installed | |
251 | bash in /usr/gnu/bin/bash, add the following line to ~/.login: | |
252 | ||
253 | if ( -f /usr/gnu/bin/bash ) exec /usr/gnu/bin/bash --login | |
254 | ||
255 | (the `--login' tells bash that it is a login shell). | |
256 | ||
257 | It's not a good idea to put this command into ~/.cshrc, because every | |
258 | csh you run without the `-f' option, even ones started to run csh scripts, | |
259 | reads that file. If you must put the command in ~/.cshrc, use something | |
260 | like | |
261 | ||
262 | if ( $?prompt ) exec /usr/gnu/bin/bash --login | |
263 | ||
264 | to ensure that bash is exec'd only when the csh is interactive. | |
265 | ||
266 | If your login shell is sh or ksh, you have to do two things. | |
267 | ||
268 | First, create an empty file in your home directory named `.bash_profile'. | |
269 | The existence of this file will prevent the exec'd bash from trying to | |
270 | read ~/.profile, and re-execing itself over and over again. ~/.bash_profile | |
271 | is the first file bash tries to read initialization commands from when | |
272 | it is invoked as a login shell. | |
273 | ||
274 | Next, add a line similar to the above to ~/.profile: | |
275 | ||
276 | [ -f /usr/gnu/bin/bash ] && [ -x /usr/gnu/bin/bash ] && \ | |
277 | exec /usr/gnu/bin/bash --login | |
278 | ||
279 | This will cause login shells to replace themselves with bash running as | |
280 | a login shell. Once you have this working, you can copy your initialization | |
281 | code from ~/.profile to ~/.bash_profile. | |
282 | ||
283 | I have received word that the recipe supplied above is insufficient for | |
284 | machines running CDE. CDE has a maze of twisty little startup files, all | |
285 | slightly different. | |
286 | ||
287 | If you cannot change your login shell in the password file to bash, you | |
288 | will have to (apparently) live with CDE using the shell in the password | |
289 | file to run its startup scripts. If you have changed your shell to bash, | |
290 | there is code in the CDE startup files (on Solaris, at least) that attempts | |
291 | to do the right thing. It is, however, often broken, and may require that | |
292 | you use the $BASH_ENV trick described below. | |
293 | ||
294 | `dtterm' claims to use $SHELL as the default program to start, so if you | |
295 | can change $SHELL in the CDE startup files, you should be able to use bash | |
296 | in your terminal windows. | |
297 | ||
298 | Setting DTSOURCEPROFILE in ~/.dtprofile will cause the `Xsession' program | |
299 | to read your login shell's startup files. You may be able to use bash for | |
300 | the rest of the CDE programs by setting SHELL to bash in ~/.dtprofile as | |
301 | well, but I have not tried this. | |
302 | ||
303 | You can use the above `exec' recipe to start bash when not logging in with | |
304 | CDE by testing the value of the DT variable: | |
305 | ||
306 | if [ -n "$DT" ]; then | |
307 | [ -f /usr/gnu/bin/bash ] && exec /usr/gnu/bin/bash --login | |
308 | fi | |
309 | ||
310 | If CDE starts its shells non-interactively during login, the login shell | |
311 | startup files (~/.profile, ~/.bash_profile) will not be sourced at login. | |
312 | To get around this problem, append a line similar to the following to your | |
313 | ~/.dtprofile: | |
314 | ||
315 | BASH_ENV=${HOME}/.bash_profile ; export BASH_ENV | |
316 | ||
317 | and add the following line to the beginning of ~/.bash_profile: | |
318 | ||
319 | unset BASH_ENV | |
320 | ||
321 | A8) I just changed my login shell to bash, and now I can't FTP into my | |
322 | machine. Why not? | |
323 | ||
324 | You must add the full pathname to bash to the file /etc/shells. As | |
325 | noted in the answer to the previous question, many systems require | |
326 | this before you can make bash your login shell. | |
327 | ||
328 | Most versions of ftpd use this file to prohibit `special' users | |
329 | such as `uucp' and `news' from using FTP. | |
330 | ||
331 | A9) What's the `POSIX 1003.2 standard'? | |
332 | ||
333 | POSIX is a name originally coined by Richard Stallman for a | |
334 | family of open system standards based on UNIX. There are a | |
335 | number of aspects of UNIX under consideration for | |
336 | standardization, from the basic system services at the system | |
337 | call and C library level to applications and tools to system | |
338 | administration and management. Each area of standardization is | |
339 | assigned to a working group in the 1003 series. | |
340 | ||
341 | The POSIX Shell and Utilities standard has been developed by IEEE | |
342 | Working Group 1003.2 (POSIX.2). It concentrates on the command | |
343 | interpreter interface and utility programs commonly executed from | |
344 | the command line or by other programs. An initial version of the | |
345 | standard has been approved and published by the IEEE, and work is | |
346 | currently underway to update it. | |
347 | ||
348 | Bash is concerned with the aspects of the shell's behavior | |
349 | defined by POSIX.2. The shell command language has of course | |
350 | been standardized, including the basic flow control and program | |
351 | execution constructs, I/O redirection and pipelining, argument | |
352 | handling, variable expansion, and quoting. | |
353 | ||
354 | The `special' builtins, which must be implemented as part of the | |
355 | shell to provide the desired functionality, are specified as | |
356 | being part of the shell; examples of these are `eval' and | |
357 | `export'. Other utilities appear in the sections of POSIX.2 not | |
358 | devoted to the shell which are commonly (and in some cases must | |
359 | be) implemented as builtin commands, such as `read' and `test'. | |
360 | POSIX.2 also specifies aspects of the shell's interactive | |
361 | behavior as part of the UPE, including job control and command | |
362 | line editing. Only vi-style line editing commands have been | |
363 | standardized; emacs editing commands were left out due to | |
364 | objections. | |
365 | ||
366 | The Open Group has made an older version of its Single Unix | |
367 | Specification (version 2), which is very similar to POSIX.2, | |
368 | available on the web at | |
369 | ||
370 | http://www.opengroup.org/onlinepubs/007908799/ | |
371 | ||
372 | The Single Unix Specification, version 3, is available on the web at | |
373 | ||
374 | http://www.opengroup.org/onlinepubs/007904975/ | |
375 | ||
376 | A10) What is the bash `posix mode'? | |
377 | ||
378 | Although bash is an implementation of the POSIX.2 shell | |
379 | specification, there are areas where the bash default behavior | |
380 | differs from that spec. The bash `posix mode' changes the bash | |
381 | behavior in these areas so that it obeys the spec more closely. | |
382 | ||
383 | Posix mode is entered by starting bash with the --posix or | |
384 | '-o posix' option or executing `set -o posix' after bash is running. | |
385 | ||
386 | The specific aspects of bash which change when posix mode is | |
387 | active are listed in the file POSIX in the bash distribution. | |
388 | They are also listed in a section in the Bash Reference Manual | |
389 | (from which that file is generated). | |
390 | ||
391 | Section B: The latest version | |
392 | ||
393 | B1) What's new in version 2.05b? | |
394 | ||
395 | The raison d'etre for bash-2.05b is to make a second intermediate | |
396 | release containing the first of the new features to be available | |
397 | in bash-3.0 and get feedback on those features before proceeding. | |
398 | The major new feature is multibyte character support in both Bash | |
399 | and Readline. | |
400 | ||
401 | Bash-2.05b contains the following new features (see the manual page for | |
402 | complete descriptions and the CHANGES and NEWS files in the bash-2.05b | |
403 | distribution): | |
404 | ||
405 | o support for multibyte characters has been added to both bash and readline | |
406 | ||
407 | o the DEBUG trap is now run *before* simple commands, ((...)) commands, | |
408 | [[...]] conditional commands, and for ((...)) loops | |
409 | ||
410 | o the shell now performs arithmetic in the largest integer size the machine | |
411 | supports (intmax_t) | |
412 | ||
413 | o there is a new \D{...} prompt expansion; passes the `...' to strftime(3) | |
414 | and inserts the result into the expanded prompt | |
415 | ||
416 | o there is a new `here-string' redirection operator: <<< word | |
417 | ||
418 | o when displaying variables, function attributes and definitions are shown | |
419 | separately, allowing them to be re-used as input (attempting to re-use | |
420 | the old output would result in syntax errors). | |
421 | ||
422 | o `read' has a new `-u fd' option to read from a specified file descriptor | |
423 | ||
424 | o the bash debugger in examples/bashdb has been modified to work with the | |
425 | new DEBUG trap semantics, the command set has been made more gdb-like, | |
426 | and the changes to $LINENO make debugging functions work better | |
427 | ||
428 | o the expansion of $LINENO inside a shell function is only relative to the | |
429 | function start if the shell is interactive -- if the shell is running a | |
430 | script, $LINENO expands to the line number in the script. This is as | |
431 | POSIX-2001 requires | |
432 | ||
433 | ||
434 | A short feature history dating from Bash-2.0: | |
435 | ||
436 | Bash-2.05a introduced the following new features: | |
437 | ||
438 | o The `printf' builtin has undergone major work | |
439 | ||
440 | o There is a new read-only `shopt' option: login_shell, which is set by | |
441 | login shells and unset otherwise | |
442 | ||
443 | o New `\A' prompt string escape sequence; expanding to time in 24-hour | |
444 | HH:MM format | |
445 | ||
446 | o New `-A group/-g' option to complete and compgen; goes group name | |
447 | completion | |
448 | ||
449 | o New [+-]O invocation option to set and unset `shopt' options at startup | |
450 | ||
451 | o ksh-like `ERR' trap | |
452 | ||
453 | o `for' loops now allow empty word lists after the `in' reserved word | |
454 | ||
455 | o new `hard' and `soft' arguments for the `ulimit' builtin | |
456 | ||
457 | o Readline can be configured to place the user at the same point on the line | |
458 | when retrieving commands from the history list | |
459 | ||
460 | o Readline can be configured to skip `hidden' files (filenames with a leading | |
461 | `.' on Unix) when performing completion | |
462 | ||
463 | Bash-2.05 introduced the following new features: | |
464 | ||
465 | o This version has once again reverted to using locales and strcoll(3) when | |
466 | processing pattern matching bracket expressions, as POSIX requires. | |
467 | o Added a new `--init-file' invocation argument as a synonym for `--rcfile', | |
468 | per the new GNU coding standards. | |
469 | o The /dev/tcp and /dev/udp redirections now accept service names as well as | |
470 | port numbers. | |
471 | o `complete' and `compgen' now take a `-o value' option, which controls some | |
472 | of the aspects of that compspec. Valid values are: | |
473 | ||
474 | default - perform bash default completion if programmable | |
475 | completion produces no matches | |
476 | dirnames - perform directory name completion if programmable | |
477 | completion produces no matches | |
478 | filenames - tell readline that the compspec produces filenames, | |
479 | so it can do things like append slashes to | |
480 | directory names and suppress trailing spaces | |
481 | o A new loadable builtin, realpath, which canonicalizes and expands symlinks | |
482 | in pathname arguments. | |
483 | o When `set' is called without options, it prints function defintions in a | |
484 | way that allows them to be reused as input. This affects `declare' and | |
485 | `declare -p' as well. This only happens when the shell is not in POSIX | |
486 | mode, since POSIX.2 forbids this behavior. | |
487 | ||
488 | Bash-2.04 introduced the following new features: | |
489 | ||
490 | o Programmable word completion with the new `complete' and `compgen' builtins; | |
491 | examples are provided in examples/complete/complete-examples | |
492 | o `history' has a new `-d' option to delete a history entry | |
493 | o `bind' has a new `-x' option to bind key sequences to shell commands | |
494 | o The prompt expansion code has new `\j' and `\l' escape sequences | |
495 | o The `no_empty_cmd_completion' shell option, if enabled, inhibits | |
496 | command completion when TAB is typed on an empty line | |
497 | o `help' has a new `-s' option to print a usage synopsis | |
498 | o New arithmetic operators: var++, var--, ++var, --var, expr1,expr2 (comma) | |
499 | o New ksh93-style arithmetic for command: | |
500 | for ((expr1 ; expr2; expr3 )); do list; done | |
501 | o `read' has new options: `-t', `-n', `-d', `-s' | |
502 | o The redirection code handles several filenames specially: /dev/fd/N, | |
503 | /dev/stdin, /dev/stdout, /dev/stderr | |
504 | o The redirection code now recognizes /dev/tcp/HOST/PORT and | |
505 | /dev/udp/HOST/PORT and tries to open a TCP or UDP socket, respectively, | |
506 | to the specified port on the specified host | |
507 | o The ${!prefix*} expansion has been implemented | |
508 | o A new FUNCNAME variable, which expands to the name of a currently-executing | |
509 | function | |
510 | o The GROUPS variable is no longer readonly | |
511 | o A new shopt `xpg_echo' variable, to control the behavior of echo with | |
512 | respect to backslash-escape sequences at runtime | |
513 | o The NON_INTERACTIVE_LOGIN_SHELLS #define has returned | |
514 | ||
515 | The version of Readline released with Bash-2.04, Readline-4.1, had several | |
516 | new features as well: | |
517 | ||
518 | o Parentheses matching is always compiled into readline, and controllable | |
519 | with the new `blink-matching-paren' variable | |
520 | o The history-search-forward and history-search-backward functions now leave | |
521 | point at the end of the line when the search string is empty, like | |
522 | reverse-search-history, and forward-search-history | |
523 | o A new function for applications: rl_on_new_line_with_prompt() | |
524 | o New variables for applications: rl_already_prompted, and rl_gnu_readline_p | |
525 | ||
526 | ||
527 | Bash-2.03 had very few new features, in keeping with the convention | |
528 | that odd-numbered releases provide mainly bug fixes. A number of new | |
529 | features were added to Readline, mostly at the request of the Cygnus | |
530 | folks. | |
531 | ||
532 | A new shopt option, `restricted_shell', so that startup files can test | |
533 | whether or not the shell was started in restricted mode | |
534 | Filename generation is now performed on the words between ( and ) in | |
535 | compound array assignments (this is really a bug fix) | |
536 | OLDPWD is now auto-exported, as POSIX.2 requires | |
537 | ENV and BASH_ENV are read-only variables in a restricted shell | |
538 | Bash may now be linked against an already-installed Readline library, | |
539 | as long as the Readline library is version 4 or newer | |
540 | All shells begun with the `--login' option will source the login shell | |
541 | startup files, even if the shell is not interactive | |
542 | ||
543 | There were lots of changes to the version of the Readline library released | |
544 | along with Bash-2.03. For a complete list of the changes, read the file | |
545 | CHANGES in the Bash-2.03 distribution. | |
546 | ||
547 | Bash-2.02 contained the following new features: | |
548 | ||
549 | a new version of malloc (based on the old GNU malloc code in previous | |
550 | bash versions) that is more page-oriented, more conservative | |
551 | with memory usage, does not `orphan' large blocks when they | |
552 | are freed, is usable on 64-bit machines, and has allocation | |
553 | checking turned on unconditionally | |
554 | POSIX.2-style globbing character classes ([:alpha:], [:alnum:], etc.) | |
555 | POSIX.2-style globbing equivalence classes | |
556 | POSIX.2-style globbing collating symbols | |
557 | the ksh [[...]] extended conditional command | |
558 | the ksh egrep-style extended pattern matching operators | |
559 | a new `printf' builtin | |
560 | the ksh-like $(<filename) command substitution, which is equivalent to | |
561 | $(cat filename) | |
562 | new tilde prefixes that expand to directories from the directory stack | |
563 | new `**' arithmetic operator to do exponentiation | |
564 | case-insensitive globbing (filename expansion) | |
565 | menu completion a la tcsh | |
566 | `magic-space' history expansion function like tcsh | |
567 | the readline inputrc `language' has a new file inclusion directive ($include) | |
568 | ||
569 | Bash-2.01 contained only a few new features: | |
570 | ||
571 | new `GROUPS' builtin array variable containing the user's group list | |
572 | new bindable readline commands: history-and-alias-expand-line and | |
573 | alias-expand-line | |
574 | ||
575 | Bash-2.0 contained extensive changes and new features from bash-1.14.7. | |
576 | Here's a short list: | |
577 | ||
578 | new `time' reserved word to time pipelines, shell builtins, and | |
579 | shell functions | |
580 | one-dimensional arrays with a new compound assignment statement, | |
581 | appropriate expansion constructs and modifications to some | |
582 | of the builtins (read, declare, etc.) to use them | |
583 | new quoting syntaxes for ANSI-C string expansion and locale-specific | |
584 | string translation | |
585 | new expansions to do substring extraction, pattern replacement, and | |
586 | indirect variable expansion | |
587 | new builtins: `disown' and `shopt' | |
588 | new variables: HISTIGNORE, SHELLOPTS, PIPESTATUS, DIRSTACK, GLOBIGNORE, | |
589 | MACHTYPE, BASH_VERSINFO | |
590 | special handling of many unused or redundant variables removed | |
591 | (e.g., $notify, $glob_dot_filenames, $no_exit_on_failed_exec) | |
592 | dynamic loading of new builtin commands; many loadable examples provided | |
593 | new prompt expansions: \a, \e, \n, \H, \T, \@, \v, \V | |
594 | history and aliases available in shell scripts | |
595 | new readline variables: enable-keypad, mark-directories, input-meta, | |
596 | visible-stats, disable-completion, comment-begin | |
597 | new readline commands to manipulate the mark and operate on the region | |
598 | new readline emacs mode commands and bindings for ksh-88 compatibility | |
599 | updated and extended builtins | |
600 | new DEBUG trap | |
601 | expanded (and now documented) restricted shell mode | |
602 | ||
603 | implementation stuff: | |
604 | autoconf-based configuration | |
605 | nearly all of the bugs reported since version 1.14 have been fixed | |
606 | most builtins converted to use builtin `getopt' for consistency | |
607 | most builtins use -p option to display output in a reusable form | |
608 | (for consistency) | |
609 | grammar tighter and smaller (66 reduce-reduce conflicts gone) | |
610 | lots of code now smaller and faster | |
611 | test suite greatly expanded | |
612 | ||
613 | B2) Are there any user-visible incompatibilities between bash-2.05b and | |
614 | bash-1.14.7? | |
615 | ||
616 | There are a few incompatibilities between version 1.14.7 and version 2.05b. | |
617 | They are detailed in the file COMPAT in the bash distribution. That file | |
618 | is not meant to be all-encompassing; send mail to bash-maintainers@gnu.org | |
619 | if if you find something that's not mentioned there. | |
620 | ||
621 | Section C: Differences from other Unix shells | |
622 | ||
623 | C1) How does bash differ from sh, the Bourne shell? | |
624 | ||
625 | This is a non-comprehensive list of features that differentiate bash | |
626 | from the SVR4.2 shell. The bash manual page explains these more | |
627 | completely. | |
628 | ||
629 | Things bash has that sh does not: | |
630 | long invocation options | |
631 | [+-]O invocation option | |
632 | -l invocation option | |
633 | `!' reserved word to invert pipeline return value | |
634 | `time' reserved word to time pipelines and shell builtins | |
635 | the `function' reserved word | |
636 | the `select' compound command and reserved word | |
637 | arithmetic for command: for ((expr1 ; expr2; expr3 )); do list; done | |
638 | new $'...' and $"..." quoting | |
639 | the $(...) form of command substitution | |
640 | the $(<filename) form of command substitution, equivalent to | |
641 | $(cat filename) | |
642 | the ${#param} parameter value length operator | |
643 | the ${!param} indirect parameter expansion operator | |
644 | the ${!param*} prefix expansion operator | |
645 | the ${param:offset[:length]} parameter substring operator | |
646 | the ${param/pat[/string]} parameter pattern substitution operator | |
647 | expansions to perform substring removal (${p%[%]w}, ${p#[#]w}) | |
648 | expansion of positional parameters beyond $9 with ${num} | |
649 | variables: BASH, BASH_VERSION, BASH_VERSINFO, UID, EUID, REPLY, | |
650 | TIMEFORMAT, PPID, PWD, OLDPWD, SHLVL, RANDOM, SECONDS, | |
651 | LINENO, HISTCMD, HOSTTYPE, OSTYPE, MACHTYPE, HOSTNAME, | |
652 | ENV, PS3, PS4, DIRSTACK, PIPESTATUS, HISTSIZE, HISTFILE, | |
653 | HISTFILESIZE, HISTCONTROL, HISTIGNORE, GLOBIGNORE, GROUPS, | |
654 | PROMPT_COMMAND, FCEDIT, FIGNORE, IGNOREEOF, INPUTRC, | |
655 | SHELLOPTS, OPTERR, HOSTFILE, TMOUT, FUNCNAME, histchars, | |
656 | auto_resume | |
657 | DEBUG trap | |
658 | ERR trap | |
659 | variable arrays with new compound assignment syntax | |
660 | redirections: <>, &>, >|, <<<, [n]<&word-, [n]>&word- | |
661 | prompt string special char translation and variable expansion | |
662 | auto-export of variables in initial environment | |
663 | command search finds functions before builtins | |
664 | bash return builtin will exit a file sourced with `.' | |
665 | builtins: cd -/-L/-P, exec -l/-c/-a, echo -e/-E, hash -d/-l/-p/-t. | |
666 | export -n/-f/-p/name=value, pwd -L/-P, | |
667 | read -e/-p/-a/-t/-n/-d/-s/-u, | |
668 | readonly -a/-f/name=value, trap -l, set +o, | |
669 | set -b/-m/-o option/-h/-p/-B/-C/-H/-P, | |
670 | unset -f/-v, ulimit -m/-p/-u, | |
671 | type -a/-p/-t/-f/-P, suspend -f, kill -n, | |
672 | test -o optname/s1 == s2/s1 < s2/s1 > s2/-nt/-ot/-ef/-O/-G/-S | |
673 | bash reads ~/.bashrc for interactive shells, $ENV for non-interactive | |
674 | bash restricted shell mode is more extensive | |
675 | bash allows functions and variables with the same name | |
676 | brace expansion | |
677 | tilde expansion | |
678 | arithmetic expansion with $((...)) and `let' builtin | |
679 | the `[[...]]' extended conditional command | |
680 | process substitution | |
681 | aliases and alias/unalias builtins | |
682 | local variables in functions and `local' builtin | |
683 | readline and command-line editing with programmable completion | |
684 | command history and history/fc builtins | |
685 | csh-like history expansion | |
686 | other new bash builtins: bind, command, compgen, complete, builtin, | |
687 | declare/typeset, dirs, enable, fc, help, | |
688 | history, logout, popd, pushd, disown, shopt, | |
689 | printf | |
690 | exported functions | |
691 | filename generation when using output redirection (command >a*) | |
692 | POSIX.2-style globbing character classes | |
693 | POSIX.2-style globbing equivalence classes | |
694 | POSIX.2-style globbing collating symbols | |
695 | egrep-like extended pattern matching operators | |
696 | case-insensitive pattern matching and globbing | |
697 | variable assignments preceding commands affect only that command, | |
698 | even for builtins and functions | |
699 | posix mode | |
700 | redirection to /dev/fd/N, /dev/stdin, /dev/stdout, /dev/stderr, | |
701 | /dev/tcp/host/port, /dev/udp/host/port | |
702 | ||
703 | Things sh has that bash does not: | |
704 | uses variable SHACCT to do shell accounting | |
705 | includes `stop' builtin (bash can use alias stop='kill -s STOP') | |
706 | `newgrp' builtin | |
707 | turns on job control if called as `jsh' | |
708 | $TIMEOUT (like bash $TMOUT) | |
709 | `^' is a synonym for `|' | |
710 | new SVR4.2 sh builtins: mldmode, priv | |
711 | ||
712 | Implementation differences: | |
713 | redirection to/from compound commands causes sh to create a subshell | |
714 | bash does not allow unbalanced quotes; sh silently inserts them at EOF | |
715 | bash does not mess with signal 11 | |
716 | sh sets (euid, egid) to (uid, gid) if -p not supplied and uid < 100 | |
717 | bash splits only the results of expansions on IFS, using POSIX.2 | |
718 | field splitting rules; sh splits all words on IFS | |
719 | sh does not allow MAILCHECK to be unset (?) | |
720 | sh does not allow traps on SIGALRM or SIGCHLD | |
721 | bash allows multiple option arguments when invoked (e.g. -x -v); | |
722 | sh allows only a single option argument (`sh -x -v' attempts | |
723 | to open a file named `-v', and, on SunOS 4.1.4, dumps core. | |
724 | On Solaris 2.4 and earlier versions, sh goes into an infinite | |
725 | loop.) | |
726 | sh exits a script if any builtin fails; bash exits only if one of | |
727 | the POSIX.2 `special' builtins fails | |
728 | ||
729 | C2) How does bash differ from the Korn shell, version ksh88? | |
730 | ||
731 | Things bash has or uses that ksh88 does not: | |
732 | long invocation options | |
733 | [-+]O invocation option | |
734 | -l invocation option | |
735 | `!' reserved word | |
736 | arithmetic for command: for ((expr1 ; expr2; expr3 )); do list; done | |
737 | arithmetic in largest machine-supported size (intmax_t) | |
738 | posix mode and posix conformance | |
739 | command hashing | |
740 | tilde expansion for assignment statements that look like $PATH | |
741 | process substitution with named pipes if /dev/fd is not available | |
742 | the ${!param} indirect parameter expansion operator | |
743 | the ${!param*} prefix expansion operator | |
744 | the ${param:offset[:length]} parameter substring operator | |
745 | the ${param/pat[/string]} parameter pattern substitution operator | |
746 | variables: BASH, BASH_VERSION, BASH_VERSINFO, UID, EUID, SHLVL, | |
747 | TIMEFORMAT, HISTCMD, HOSTTYPE, OSTYPE, MACHTYPE, | |
748 | HISTFILESIZE, HISTIGNORE, HISTCONTROL, PROMPT_COMMAND, | |
749 | IGNOREEOF, FIGNORE, INPUTRC, HOSTFILE, DIRSTACK, | |
750 | PIPESTATUS, HOSTNAME, OPTERR, SHELLOPTS, GLOBIGNORE, | |
751 | GROUPS, FUNCNAME, histchars, auto_resume | |
752 | prompt expansion with backslash escapes and command substitution | |
753 | redirection: &> (stdout and stderr), <<<, [n]<&word-, [n]>&word- | |
754 | more extensive and extensible editing and programmable completion | |
755 | builtins: bind, builtin, command, declare, dirs, echo -e/-E, enable, | |
756 | exec -l/-c/-a, fc -s, export -n/-f/-p, hash, help, history, | |
757 | jobs -x/-r/-s, kill -s/-n/-l, local, logout, popd, pushd, | |
758 | read -e/-p/-a/-t/-n/-d/-s, readonly -a/-n/-f/-p, | |
759 | set -o braceexpand/-o histexpand/-o interactive-comments/ | |
760 | -o notify/-o physical/-o posix/-o hashall/-o onecmd/ | |
761 | -h/-B/-C/-b/-H/-P, set +o, suspend, trap -l, type, | |
762 | typeset -a/-F/-p, ulimit -u, umask -S, alias -p, shopt, | |
763 | disown, printf, complete, compgen | |
764 | `!' csh-style history expansion | |
765 | POSIX.2-style globbing character classes | |
766 | POSIX.2-style globbing equivalence classes | |
767 | POSIX.2-style globbing collating symbols | |
768 | egrep-like extended pattern matching operators | |
769 | case-insensitive pattern matching and globbing | |
770 | `**' arithmetic operator to do exponentiation | |
771 | redirection to /dev/fd/N, /dev/stdin, /dev/stdout, /dev/stderr | |
772 | arrays of unlimited size | |
773 | TMOUT is default timeout for `read' and `select' | |
774 | ||
775 | Things ksh88 has or uses that bash does not: | |
776 | tracked aliases (alias -t) | |
777 | variables: ERRNO, FPATH, EDITOR, VISUAL | |
778 | co-processes (|&, >&p, <&p) | |
779 | weirdly-scoped functions | |
780 | typeset +f to list all function names without definitions | |
781 | text of command history kept in a file, not memory | |
782 | builtins: alias -x, cd old new, fc -e -, newgrp, print, | |
783 | read -p/-s/var?prompt, set -A/-o gmacs/ | |
784 | -o bgnice/-o markdirs/-o nolog/-o trackall/-o viraw/-s, | |
785 | typeset -H/-L/-R/-Z/-A/-ft/-fu/-fx/-l/-u/-t, whence | |
786 | using environment to pass attributes of exported variables | |
787 | arithmetic evaluation done on arguments to some builtins | |
788 | reads .profile from $PWD when invoked as login shell | |
789 | ||
790 | Implementation differences: | |
791 | ksh runs last command of a pipeline in parent shell context | |
792 | bash has brace expansion by default (ksh88 compile-time option) | |
793 | bash has fixed startup file for all interactive shells; ksh reads $ENV | |
794 | bash has exported functions | |
795 | bash command search finds functions before builtins | |
796 | bash waits for all commands in pipeline to exit before returning status | |
797 | emacs-mode editing has some slightly different key bindings | |
798 | ||
799 | C3) Which new features in ksh-93 are not in bash, and which are? | |
800 | ||
801 | New things in ksh-93 not in bash-2.05b: | |
802 | associative arrays | |
803 | floating point arithmetic and variables | |
804 | math library functions | |
805 | ${!name[sub]} name of subscript for associative array | |
806 | `.' is allowed in variable names to create a hierarchical namespace | |
807 | more extensive compound assignment syntax | |
808 | discipline functions | |
809 | `sleep' and `getconf' builtins (bash has loadable versions) | |
810 | typeset -n and `nameref' variables | |
811 | KEYBD trap | |
812 | variables: .sh.edchar, .sh.edmode, .sh.edcol, .sh.edtext, .sh.version, | |
813 | .sh.name, .sh.subscript, .sh.value, .sh.match, HISTEDIT | |
814 | backreferences in pattern matching (\N) | |
815 | `&' operator in pattern lists for matching | |
816 | print -f (bash uses printf) | |
817 | `fc' has been renamed to `hist' | |
818 | `.' can execute shell functions | |
819 | exit statuses between 0 and 255 | |
820 | set -o pipefail | |
821 | `+=' variable assignment operator | |
822 | FPATH and PATH mixing | |
823 | getopts -a | |
824 | -I invocation option | |
825 | DEBUG trap now executed before each simple command, instead of after | |
826 | printf %H, %P, %T, %Z modifiers, output base for %d | |
827 | lexical scoping for local variables in `ksh' functions | |
828 | no scoping for local variables in `POSIX' functions | |
829 | ||
830 | New things in ksh-93 present in bash-2.05b: | |
831 | [n]<&word- and [n]>&word- redirections (combination dup and close) | |
832 | for (( expr1; expr2; expr3 )) ; do list; done - arithmetic for command | |
833 | ?:, ++, --, `expr1 , expr2' arithmetic operators | |
834 | expansions: ${!param}, ${param:offset[:len]}, ${param/pat[/str]}, | |
835 | ${!param*} | |
836 | compound array assignment | |
837 | the `!' reserved word | |
838 | loadable builtins -- but ksh uses `builtin' while bash uses `enable' | |
839 | `command', `builtin', `disown' builtins | |
840 | new $'...' and $"..." quoting | |
841 | FIGNORE (but bash uses GLOBIGNORE), HISTCMD | |
842 | set -o notify/-C | |
843 | changes to kill builtin | |
844 | read -A (bash uses read -a) | |
845 | read -t/-d | |
846 | trap -p | |
847 | exec -c/-a | |
848 | `.' restores the positional parameters when it completes | |
849 | POSIX.2 `test' | |
850 | umask -S | |
851 | unalias -a | |
852 | command and arithmetic substitution performed on PS1, PS4, and ENV | |
853 | command name completion | |
854 | ENV processed only for interactive shells | |
855 | ||
856 | Section D: Why does bash do some things differently than other Unix shells? | |
857 | ||
858 | D1) Why does bash run a different version of `command' than | |
859 | `which command' says it will? | |
860 | ||
861 | On many systems, `which' is actually a csh script that assumes | |
862 | you're running csh. In tcsh, `which' and its cousin `where' | |
863 | are builtins. On other Unix systems, `which' is a perl script | |
864 | that uses the PATH environment variable. | |
865 | ||
866 | The csh script version reads the csh startup files from your | |
867 | home directory and uses those to determine which `command' will | |
868 | be invoked. Since bash doesn't use any of those startup files, | |
869 | there's a good chance that your bash environment differs from | |
870 | your csh environment. The bash `type' builtin does everything | |
871 | `which' does, and will report correct results for the running | |
872 | shell. If you're really wedded to the name `which', try adding | |
873 | the following function definition to your .bashrc: | |
874 | ||
875 | which() | |
876 | { | |
877 | builtin type "$@" | |
878 | } | |
879 | ||
880 | If you're moving from tcsh and would like to bring `where' along | |
881 | as well, use this function: | |
882 | ||
883 | where() | |
884 | { | |
885 | builtin type -a "$@" | |
886 | } | |
887 | ||
888 | D2) Why doesn't bash treat brace expansions exactly like csh? | |
889 | ||
890 | The only difference between bash and csh brace expansion is that | |
891 | bash requires a brace expression to contain at least one unquoted | |
892 | comma if it is to be expanded. Any brace-surrounded word not | |
893 | containing an unquoted comma is left unchanged by the brace | |
894 | expansion code. This affords the greatest degree of sh | |
895 | compatibility. | |
896 | ||
897 | Bash, ksh, zsh, and pd-ksh all implement brace expansion this way. | |
898 | ||
899 | D3) Why doesn't bash have csh variable modifiers? | |
900 | ||
901 | Posix has specified a more powerful, albeit somewhat more cryptic, | |
902 | mechanism cribbed from ksh, and bash implements it. | |
903 | ||
904 | ${parameter%word} | |
905 | Remove smallest suffix pattern. The WORD is expanded to produce | |
906 | a pattern. It then expands to the value of PARAMETER, with the | |
907 | smallest portion of the suffix matched by the pattern deleted. | |
908 | ||
909 | x=file.c | |
910 | echo ${x%.c}.o | |
911 | -->file.o | |
912 | ||
913 | ${parameter%%word} | |
914 | ||
915 | Remove largest suffix pattern. The WORD is expanded to produce | |
916 | a pattern. It then expands to the value of PARAMETER, with the | |
917 | largest portion of the suffix matched by the pattern deleted. | |
918 | ||
919 | x=posix/src/std | |
920 | echo ${x%%/*} | |
921 | -->posix | |
922 | ||
923 | ${parameter#word} | |
924 | Remove smallest prefix pattern. The WORD is expanded to produce | |
925 | a pattern. It then expands to the value of PARAMETER, with the | |
926 | smallest portion of the prefix matched by the pattern deleted. | |
927 | ||
928 | x=$HOME/src/cmd | |
929 | echo ${x#$HOME} | |
930 | -->/src/cmd | |
931 | ||
932 | ${parameter##word} | |
933 | Remove largest prefix pattern. The WORD is expanded to produce | |
934 | a pattern. It then expands to the value of PARAMETER, with the | |
935 | largest portion of the prefix matched by the pattern deleted. | |
936 | ||
937 | x=/one/two/three | |
938 | echo ${x##*/} | |
939 | -->three | |
940 | ||
941 | ||
942 | Given | |
943 | a=/a/b/c/d | |
944 | b=b.xxx | |
945 | ||
946 | csh bash result | |
947 | --- ---- ------ | |
948 | $a:h ${a%/*} /a/b/c | |
949 | $a:t ${a##*/} d | |
950 | $b:r ${b%.*} b | |
951 | $b:e ${b##*.} xxx | |
952 | ||
953 | ||
954 | D4) How can I make my csh aliases work when I convert to bash? | |
955 | ||
956 | Bash uses a different syntax to support aliases than csh does. | |
957 | The details can be found in the documentation. We have provided | |
958 | a shell script which does most of the work of conversion for you; | |
959 | this script can be found in ./examples/misc/aliasconv.sh. Here is | |
960 | how you use it: | |
961 | ||
962 | Start csh in the normal way for you. (e.g., `csh') | |
963 | ||
964 | Pipe the output of `alias' through `aliasconv.sh', saving the | |
965 | results into `bash_aliases': | |
966 | ||
967 | alias | bash aliasconv.sh >bash_aliases | |
968 | ||
969 | Edit `bash_aliases', carefully reading through any created | |
970 | functions. You will need to change the names of some csh specific | |
971 | variables to the bash equivalents. The script converts $cwd to | |
972 | $PWD, $term to $TERM, $home to $HOME, $user to $USER, and $prompt | |
973 | to $PS1. You may also have to add quotes to avoid unwanted | |
974 | expansion. | |
975 | ||
976 | For example, the csh alias: | |
977 | ||
978 | alias cd 'cd \!*; echo $cwd' | |
979 | ||
980 | is converted to the bash function: | |
981 | ||
982 | cd () { command cd "$@"; echo $PWD ; } | |
983 | ||
984 | The only thing that needs to be done is to quote $PWD: | |
985 | ||
986 | cd () { command cd "$@"; echo "$PWD" ; } | |
987 | ||
988 | Merge the edited file into your ~/.bashrc. | |
989 | ||
990 | There is an additional, more ambitious, script in | |
991 | examples/misc/cshtobash that attempts to convert your entire csh | |
992 | environment to its bash equivalent. This script can be run as | |
993 | simply `cshtobash' to convert your normal interactive | |
994 | environment, or as `cshtobash ~/.login' to convert your login | |
995 | environment. | |
996 | ||
997 | D5) How can I pipe standard output and standard error from one command to | |
998 | another, like csh does with `|&'? | |
999 | ||
1000 | Use | |
1001 | command 2>&1 | command2 | |
1002 | ||
1003 | The key is to remember that piping is performed before redirection, so | |
1004 | file descriptor 1 points to the pipe when it is duplicated onto file | |
1005 | descriptor 2. | |
1006 | ||
1007 | D6) Now that I've converted from ksh to bash, are there equivalents to | |
1008 | ksh features like autoloaded functions and the `whence' command? | |
1009 | ||
1010 | There are features in ksh-88 and ksh-93 that do not have direct bash | |
1011 | equivalents. Most, however, can be emulated with very little trouble. | |
1012 | ||
1013 | ksh-88 feature Bash equivalent | |
1014 | -------------- --------------- | |
1015 | compiled-in aliases set up aliases in .bashrc; some ksh aliases are | |
1016 | bash builtins (hash, history, type) | |
1017 | coprocesses named pipe pairs (one for read, one for write) | |
1018 | typeset +f declare -F | |
1019 | cd, print, whence function substitutes in examples/functions/kshenv | |
1020 | autoloaded functions examples/functions/autoload is the same as typeset -fu | |
1021 | read var?prompt read -p prompt var | |
1022 | ||
1023 | ksh-93 feature Bash equivalent | |
1024 | -------------- --------------- | |
1025 | sleep, getconf Bash has loadable versions in examples/loadables | |
1026 | ${.sh.version} $BASH_VERSION | |
1027 | print -f printf | |
1028 | hist alias hist=fc | |
1029 | $HISTEDIT $FCEDIT | |
1030 | ||
1031 | Section E: How can I get bash to do certain things, and why does bash do | |
1032 | things the way it does? | |
1033 | ||
1034 | E1) Why is the bash builtin `test' slightly different from /bin/test? | |
1035 | ||
1036 | The specific example used here is [ ! x -o x ], which is false. | |
1037 | ||
1038 | Bash's builtin `test' implements the Posix.2 spec, which can be | |
1039 | summarized as follows (the wording is due to David Korn): | |
1040 | ||
1041 | Here is the set of rules for processing test arguments. | |
1042 | ||
1043 | 0 Args: False | |
1044 | 1 Arg: True iff argument is not null. | |
1045 | 2 Args: If first arg is !, True iff second argument is null. | |
1046 | If first argument is unary, then true if unary test is true | |
1047 | Otherwise error. | |
1048 | 3 Args: If second argument is a binary operator, do binary test of $1 $3 | |
1049 | If first argument is !, negate two argument test of $2 $3 | |
1050 | If first argument is `(' and third argument is `)', do the | |
1051 | one-argument test of the second argument. | |
1052 | Otherwise error. | |
1053 | 4 Args: If first argument is !, negate three argument test of $2 $3 $4. | |
1054 | Otherwise unspecified | |
1055 | 5 or more Args: unspecified. (Historical shells would use their | |
1056 | current algorithm). | |
1057 | ||
1058 | The operators -a and -o are considered binary operators for the purpose | |
1059 | of the 3 Arg case. | |
1060 | ||
1061 | As you can see, the test becomes (not (x or x)), which is false. | |
1062 | ||
1063 | E2) Why does bash sometimes say `Broken pipe'? | |
1064 | ||
1065 | If a sequence of commands appears in a pipeline, and one of the | |
1066 | reading commands finishes before the writer has finished, the | |
1067 | writer receives a SIGPIPE signal. Many other shells special-case | |
1068 | SIGPIPE as an exit status in the pipeline and do not report it. | |
1069 | For example, in: | |
1070 | ||
1071 | ps -aux | head | |
1072 | ||
1073 | `head' can finish before `ps' writes all of its output, and ps | |
1074 | will try to write on a pipe without a reader. In that case, bash | |
1075 | will print `Broken pipe' to stderr when ps is killed by a | |
1076 | SIGPIPE. | |
1077 | ||
1078 | You can build a version of bash that will not report SIGPIPE errors | |
1079 | by uncommenting the definition of DONT_REPORT_SIGPIPE in the file | |
1080 | config-top.h. | |
1081 | ||
1082 | E3) When I have terminal escape sequences in my prompt, why does bash | |
1083 | wrap lines at the wrong column? | |
1084 | ||
1085 | Readline, the line editing library that bash uses, does not know | |
1086 | that the terminal escape sequences do not take up space on the | |
1087 | screen. The redisplay code assumes, unless told otherwise, that | |
1088 | each character in the prompt is a `printable' character that | |
1089 | takes up one character position on the screen. | |
1090 | ||
1091 | You can use the bash prompt expansion facility (see the PROMPTING | |
1092 | section in the manual page) to tell readline that sequences of | |
1093 | characters in the prompt strings take up no screen space. | |
1094 | ||
1095 | Use the \[ escape to begin a sequence of non-printing characters, | |
1096 | and the \] escape to signal the end of such a sequence. | |
1097 | ||
1098 | E4) If I pipe the output of a command into `read variable', why doesn't | |
1099 | the output show up in $variable when the read command finishes? | |
1100 | ||
1101 | This has to do with the parent-child relationship between Unix | |
1102 | processes. It affects all commands run in pipelines, not just | |
1103 | simple calls to `read'. For example, piping a command's output | |
1104 | into a `while' loop that repeatedly calls `read' will result in | |
1105 | the same behavior. | |
1106 | ||
1107 | Each element of a pipeline runs in a separate process, a child of | |
1108 | the shell running the pipeline. A subprocess cannot affect its | |
1109 | parent's environment. When the `read' command sets the variable | |
1110 | to the input, that variable is set only in the subshell, not the | |
1111 | parent shell. When the subshell exits, the value of the variable | |
1112 | is lost. | |
1113 | ||
1114 | Many pipelines that end with `read variable' can be converted | |
1115 | into command substitutions, which will capture the output of | |
1116 | a specified command. The output can then be assigned to a | |
1117 | variable: | |
1118 | ||
1119 | grep ^gnu /usr/lib/news/active | wc -l | read ngroup | |
1120 | ||
1121 | can be converted into | |
1122 | ||
1123 | ngroup=$(grep ^gnu /usr/lib/news/active | wc -l) | |
1124 | ||
1125 | This does not, unfortunately, work to split the text among | |
1126 | multiple variables, as read does when given multiple variable | |
1127 | arguments. If you need to do this, you can either use the | |
1128 | command substitution above to read the output into a variable | |
1129 | and chop up the variable using the bash pattern removal | |
1130 | expansion operators or use some variant of the following | |
1131 | approach. | |
1132 | ||
1133 | Say /usr/local/bin/ipaddr is the following shell script: | |
1134 | ||
1135 | #! /bin/sh | |
1136 | host `hostname` | awk '/address/ {print $NF}' | |
1137 | ||
1138 | Instead of using | |
1139 | ||
1140 | /usr/local/bin/ipaddr | read A B C D | |
1141 | ||
1142 | to break the local machine's IP address into separate octets, use | |
1143 | ||
1144 | OIFS="$IFS" | |
1145 | IFS=. | |
1146 | set -- $(/usr/local/bin/ipaddr) | |
1147 | IFS="$OIFS" | |
1148 | A="$1" B="$2" C="$3" D="$4" | |
1149 | ||
1150 | Beware, however, that this will change the shell's positional | |
1151 | parameters. If you need them, you should save them before doing | |
1152 | this. | |
1153 | ||
1154 | This is the general approach -- in most cases you will not need to | |
1155 | set $IFS to a different value. | |
1156 | ||
1157 | Some other user-supplied alternatives include: | |
1158 | ||
1159 | read A B C D << HERE | |
1160 | $(IFS=.; echo $(/usr/local/bin/ipaddr)) | |
1161 | HERE | |
1162 | ||
1163 | and, where process substitution is available, | |
1164 | ||
1165 | read A B C D < <(IFS=.; echo $(/usr/local/bin/ipaddr)) | |
1166 | ||
1167 | E5) I have a bunch of shell scripts that use backslash-escaped characters | |
1168 | in arguments to `echo'. Bash doesn't interpret these characters. Why | |
1169 | not, and how can I make it understand them? | |
1170 | ||
1171 | This is the behavior of echo on most Unix System V machines. | |
1172 | ||
1173 | The bash builtin `echo' is modeled after the 9th Edition | |
1174 | Research Unix version of `echo'. It does not interpret | |
1175 | backslash-escaped characters in its argument strings by default; | |
1176 | it requires the use of the -e option to enable the | |
1177 | interpretation. The System V echo provides no way to disable the | |
1178 | special characters; the bash echo has a -E option to disable | |
1179 | them. | |
1180 | ||
1181 | There is a configuration option that will make bash behave like | |
1182 | the System V echo and interpret things like `\t' by default. Run | |
1183 | configure with the --enable-xpg-echo-default option to turn this | |
1184 | on. Be aware that this will cause some of the tests run when you | |
1185 | type `make tests' to fail. | |
1186 | ||
1187 | There is a shell option, `xpg_echo', settable with `shopt', that will | |
1188 | change the behavior of echo at runtime. Enabling this option turns | |
1189 | on expansion of backslash-escape sequences. | |
1190 | ||
1191 | E6) Why doesn't a while or for loop get suspended when I type ^Z? | |
1192 | ||
1193 | This is a consequence of how job control works on Unix. The only | |
1194 | thing that can be suspended is the process group. This is a single | |
1195 | command or pipeline of commands that the shell forks and executes. | |
1196 | ||
1197 | When you run a while or for loop, the only thing that the shell forks | |
1198 | and executes are any commands in the while loop test and commands in | |
1199 | the loop bodies. These, therefore, are the only things that can be | |
1200 | suspended when you type ^Z. | |
1201 | ||
1202 | If you want to be able to stop the entire loop, you need to put it | |
1203 | within parentheses, which will force the loop into a subshell that | |
1204 | may be stopped (and subsequently restarted) as a single unit. | |
1205 | ||
1206 | E7) What about empty for loops in Makefiles? | |
1207 | ||
1208 | It's fairly common to see constructs like this in automatically-generated | |
1209 | Makefiles: | |
1210 | ||
1211 | SUBDIRS = @SUBDIRS@ | |
1212 | ||
1213 | ... | |
1214 | ||
1215 | subdirs-clean: | |
1216 | for d in ${SUBDIRS}; do \ | |
1217 | ( cd $$d && ${MAKE} ${MFLAGS} clean ) \ | |
1218 | done | |
1219 | ||
1220 | When SUBDIRS is empty, this results in a command like this being passed to | |
1221 | bash: | |
1222 | ||
1223 | for d in ; do | |
1224 | ( cd $d && ${MAKE} ${MFLAGS} clean ) | |
1225 | done | |
1226 | ||
1227 | In versions of bash before bash-2.05a, this was a syntax error. If the | |
1228 | reserved word `in' was present, a word must follow it before the semicolon | |
1229 | or newline. The language in the manual page referring to the list of words | |
1230 | being empty referred to the list after it is expanded. These versions of | |
1231 | bash required that there be at least one word following the `in' when the | |
1232 | construct was parsed. | |
1233 | ||
1234 | The idiomatic Makefile solution is something like: | |
1235 | ||
1236 | SUBDIRS = @SUBDIRS@ | |
1237 | ||
1238 | subdirs-clean: | |
1239 | subdirs=$SUBDIRS ; for d in $$subdirs; do \ | |
1240 | ( cd $$d && ${MAKE} ${MFLAGS} clean ) \ | |
1241 | done | |
1242 | ||
1243 | The latest drafts of the updated POSIX standard have changed this: the | |
1244 | word list is no longer required. Bash versions 2.05a and later accept | |
1245 | the new syntax. | |
1246 | ||
1247 | E8) Why does the arithmetic evaluation code complain about `08'? | |
1248 | ||
1249 | The bash arithmetic evaluation code (used for `let', $(()), (()), and in | |
1250 | other places), interprets a leading `0' in numeric constants as denoting | |
1251 | an octal number, and a leading `0x' as denoting hexadecimal. This is | |
1252 | in accordance with the POSIX.2 spec, section 2.9.2.1, which states that | |
1253 | arithmetic constants should be handled as signed long integers as defined | |
1254 | by the ANSI/ISO C standard. | |
1255 | ||
1256 | The POSIX.2 interpretation committee has confirmed this: | |
1257 | ||
1258 | http://www.pasc.org/interps/unofficial/db/p1003.2/pasc-1003.2-173.html | |
1259 | ||
1260 | E9) Why does the pattern matching expression [A-Z]* match files beginning | |
1261 | with every letter except `z'? | |
1262 | ||
1263 | Bash-2.03, Bash-2.05 and later versions honor the current locale setting | |
1264 | when processing ranges within pattern matching bracket expressions ([A-Z]). | |
1265 | This is what POSIX.2 and SUSv3/XPG6 specify. | |
1266 | ||
1267 | The behavior of the matcher in bash-2.05 and later versions depends on the | |
1268 | current LC_COLLATE setting. Setting this variable to `C' or `POSIX' will | |
1269 | result in the traditional behavior ([A-Z] matches all uppercase ASCII | |
1270 | characters). Many other locales, including the en_US locale (the default | |
1271 | on many US versions of Linux) collate the upper and lower case letters like | |
1272 | this: | |
1273 | ||
1274 | AaBb...Zz | |
1275 | ||
1276 | which means that [A-Z] matches every letter except `z'. Others collate like | |
1277 | ||
1278 | aAbBcC...zZ | |
1279 | ||
1280 | which means that [A-Z] matches every letter except `a'. | |
1281 | ||
1282 | The portable way to specify upper case letters is [:upper:] instead of | |
1283 | A-Z; lower case may be specified as [:lower:] instead of a-z. | |
1284 | ||
1285 | Look at the manual pages for setlocale(3), strcoll(3), and, if it is | |
1286 | present, locale(1). If you have locale(1), you can use it to find | |
1287 | your current locale information even if you do not have any of the | |
1288 | LC_ variables set. | |
1289 | ||
1290 | My advice is to put | |
1291 | ||
1292 | export LC_COLLATE=C | |
1293 | ||
1294 | into /etc/profile and inspect any shell scripts run from cron for | |
1295 | constructs like [A-Z]. This will prevent things like | |
1296 | ||
1297 | rm [A-Z]* | |
1298 | ||
1299 | from removing every file in the current directory except those beginning | |
1300 | with `z' and still allow individual users to change the collation order. | |
1301 | Users may put the above command into their own profiles as well, of course. | |
1302 | ||
1303 | E10) Why does `cd //' leave $PWD as `//'? | |
1304 | ||
1305 | POSIX.2, in its description of `cd', says that *three* or more leading | |
1306 | slashes may be replaced with a single slash when canonicalizing the | |
1307 | current working directory. | |
1308 | ||
1309 | This is, I presume, for historical compatibility. Certain versions of | |
1310 | Unix, and early network file systems, used paths of the form | |
1311 | //hostname/path to access `path' on server `hostname'. | |
1312 | ||
1313 | E11) If I resize my xterm while another program is running, why doesn't bash | |
1314 | notice the change? | |
1315 | ||
1316 | This is another issue that deals with job control. | |
1317 | ||
1318 | The kernel maintains a notion of a current terminal process group. Members | |
1319 | of this process group (processes whose process group ID is equal to the | |
1320 | current terminal process group ID) receive terminal-generated signals like | |
1321 | SIGWINCH. (For more details, see the JOB CONTROL section of the bash | |
1322 | man page.) | |
1323 | ||
1324 | If a terminal is resized, the kernel sends SIGWINCH to each member of | |
1325 | the terminal's current process group (the `foreground' process group). | |
1326 | ||
1327 | When bash is running with job control enabled, each pipeline (which may be | |
1328 | a single command) is run in its own process group, different from bash's | |
1329 | process group. This foreground process group receives the SIGWINCH; bash | |
1330 | does not. Bash has no way of knowing that the terminal has been resized. | |
1331 | ||
1332 | There is a `checkwinsize' option, settable with the `shopt' builtin, that | |
1333 | will cause bash to check the window size and adjust its idea of the | |
1334 | terminal's dimensions each time a process stops or exits and returns control | |
1335 | of the terminal to bash. Enable it with `shopt -s checkwinsize'. | |
1336 | ||
1337 | Section F: Things to watch out for on certain Unix versions | |
1338 | ||
1339 | F1) Why can't I use command line editing in my `cmdtool'? | |
1340 | ||
1341 | The problem is `cmdtool' and bash fighting over the input. When | |
1342 | scrolling is enabled in a cmdtool window, cmdtool puts the tty in | |
1343 | `raw mode' to permit command-line editing using the mouse for | |
1344 | applications that cannot do it themselves. As a result, bash and | |
1345 | cmdtool each try to read keyboard input immediately, with neither | |
1346 | getting enough of it to be useful. | |
1347 | ||
1348 | This mode also causes cmdtool to not implement many of the | |
1349 | terminal functions and control sequences appearing in the | |
1350 | `sun-cmd' termcap entry. For a more complete explanation, see | |
1351 | that file examples/suncmd.termcap in the bash distribution. | |
1352 | ||
1353 | `xterm' is a better choice, and gets along with bash much more | |
1354 | smoothly. | |
1355 | ||
1356 | If you must use cmdtool, you can use the termcap description in | |
1357 | examples/suncmd.termcap. Set the TERMCAP variable to the terminal | |
1358 | description contained in that file, i.e. | |
1359 | ||
1360 | TERMCAP='Mu|sun-cmd:am:bs:km:pt:li#34:co#80:cl=^L:ce=\E[K:cd=\E[J:rs=\E[s:' | |
1361 | ||
1362 | Then export TERMCAP and start a new cmdtool window from that shell. | |
1363 | The bash command-line editing should behave better in the new | |
1364 | cmdtool. If this works, you can put the assignment to TERMCAP | |
1365 | in your bashrc file. | |
1366 | ||
1367 | F2) I built bash on Solaris 2. Why do globbing expansions and filename | |
1368 | completion chop off the first few characters of each filename? | |
1369 | ||
1370 | This is the consequence of building bash on SunOS 5 and linking | |
1371 | with the libraries in /usr/ucblib, but using the definitions | |
1372 | and structures from files in /usr/include. | |
1373 | ||
1374 | The actual conflict is between the dirent structure in | |
1375 | /usr/include/dirent.h and the struct returned by the version of | |
1376 | `readdir' in libucb.a (a 4.3-BSD style `struct direct'). | |
1377 | ||
1378 | Make sure you've got /usr/ccs/bin ahead of /usr/ucb in your $PATH | |
1379 | when configuring and building bash. This will ensure that you | |
1380 | use /usr/ccs/bin/cc or acc instead of /usr/ucb/cc and that you | |
1381 | link with libc before libucb. | |
1382 | ||
1383 | If you have installed the Sun C compiler, you may also need to | |
1384 | put /usr/ccs/bin and /opt/SUNWspro/bin into your $PATH before | |
1385 | /usr/ucb. | |
1386 | ||
1387 | F3) Why does bash dump core after I interrupt username completion or | |
1388 | `~user' tilde expansion on a machine running NIS? | |
1389 | ||
1390 | This is a famous and long-standing bug in the SunOS YP (sorry, NIS) | |
1391 | client library, which is part of libc. | |
1392 | ||
1393 | The YP library code keeps static state -- a pointer into the data | |
1394 | returned from the server. When YP initializes itself (setpwent), | |
1395 | it looks at this pointer and calls free on it if it's non-null. | |
1396 | So far, so good. | |
1397 | ||
1398 | If one of the YP functions is interrupted during getpwent (the | |
1399 | exact function is interpretwithsave()), and returns NULL, the | |
1400 | pointer is freed without being reset to NULL, and the function | |
1401 | returns. The next time getpwent is called, it sees that this | |
1402 | pointer is non-null, calls free, and the bash free() blows up | |
1403 | because it's being asked to free freed memory. | |
1404 | ||
1405 | The traditional Unix mallocs allow memory to be freed multiple | |
1406 | times; that's probably why this has never been fixed. You can | |
1407 | run configure with the `--without-gnu-malloc' option to use | |
1408 | the C library malloc and avoid the problem. | |
1409 | ||
1410 | F4) I'm running SVR4.2. Why is the line erased every time I type `@'? | |
1411 | ||
1412 | The `@' character is the default `line kill' character in most | |
1413 | versions of System V, including SVR4.2. You can change this | |
1414 | character to whatever you want using `stty'. For example, to | |
1415 | change the line kill character to control-u, type | |
1416 | ||
1417 | stty kill ^U | |
1418 | ||
1419 | where the `^' and `U' can be two separate characters. | |
1420 | ||
1421 | F5) Why does bash report syntax errors when my C News scripts use a | |
1422 | redirection before a subshell command? | |
1423 | ||
1424 | The actual command in question is something like | |
1425 | ||
1426 | < file ( command ) | |
1427 | ||
1428 | According to the grammar given in the POSIX.2 standard, this construct | |
1429 | is, in fact, a syntax error. Redirections may only precede `simple | |
1430 | commands'. A subshell construct such as the above is one of the shell's | |
1431 | `compound commands'. A redirection may only follow a compound command. | |
1432 | ||
1433 | This affects the mechanical transformation of commands that use `cat' | |
1434 | to pipe a file into a command (a favorite Useless-Use-Of-Cat topic on | |
1435 | comp.unix.shell). While most commands of the form | |
1436 | ||
1437 | cat file | command | |
1438 | ||
1439 | can be converted to `< file command', shell control structures such as | |
1440 | loops and subshells require `command < file'. | |
1441 | ||
1442 | The file CWRU/sh-redir-hack in the bash-2.05a distribution is an | |
1443 | (unofficial) patch to parse.y that will modify the grammar to | |
1444 | support this construct. It will not apply with `patch'; you must | |
1445 | modify parse.y by hand. Note that if you apply this, you must | |
1446 | recompile with -DREDIRECTION_HACK. This introduces a large | |
1447 | number of reduce/reduce conflicts into the shell grammar. | |
1448 | ||
1449 | F6) Why can't I use vi-mode editing on Red Hat Linux 6.1? | |
1450 | ||
1451 | The short answer is that Red Hat screwed up. | |
1452 | ||
1453 | The long answer is that they shipped an /etc/inputrc that only works | |
1454 | for emacs mode editing, and then screwed all the vi users by setting | |
1455 | INPUTRC to /etc/inputrc in /etc/profile. | |
1456 | ||
1457 | The short fix is to do one of the following: remove or rename | |
1458 | /etc/inputrc, set INPUTRC=~/.inputrc in ~/.bashrc (or .bash_profile, | |
1459 | but make sure you export it if you do), remove the assignment to | |
1460 | INPUTRC from /etc/profile, add | |
1461 | ||
1462 | set keymap emacs | |
1463 | ||
1464 | to the beginning of /etc/inputrc, or bracket the key bindings in | |
1465 | /etc/inputrc with these lines | |
1466 | ||
1467 | $if mode=emacs | |
1468 | [...] | |
1469 | $endif | |
1470 | ||
1471 | F7) Why do bash-2.05a and bash-2.05b fail to compile `printf.def' on | |
1472 | HP/UX 11.x? | |
1473 | ||
1474 | HP/UX's support for long double is imperfect at best. | |
1475 | ||
1476 | GCC will support it without problems, but the HP C library functions | |
1477 | like strtold(3) and printf(3) don't actually work with long doubles. | |
1478 | HP implemented a `long_double' type as a 4-element array of 32-bit | |
1479 | ints, and that is what the library functions use. The ANSI C | |
1480 | `long double' type is a 128-bit floating point scalar. | |
1481 | ||
1482 | The easiest fix, until HP fixes things up, is to edit the generated | |
1483 | config.h and #undef the HAVE_LONG_DOUBLE line. After doing that, | |
1484 | the compilation should complete successfully. | |
1485 | ||
1486 | Section G: How can I get bash to do certain common things? | |
1487 | ||
1488 | G1) How can I get bash to read and display eight-bit characters? | |
1489 | ||
1490 | This is a process requiring several steps. | |
1491 | ||
1492 | First, you must ensure that the `physical' data path is a full eight | |
1493 | bits. For xterms, for example, the `vt100' resources `eightBitInput' | |
1494 | and `eightBitOutput' should be set to `true'. | |
1495 | ||
1496 | Once you have set up an eight-bit path, you must tell the kernel and | |
1497 | tty driver to leave the eighth bit of characters alone when processing | |
1498 | keyboard input. Use `stty' to do this: | |
1499 | ||
1500 | stty cs8 -istrip -parenb | |
1501 | ||
1502 | For old BSD-style systems, you can use | |
1503 | ||
1504 | stty pass8 | |
1505 | ||
1506 | You may also need | |
1507 | ||
1508 | stty even odd | |
1509 | ||
1510 | Finally, you need to tell readline that you will be inputting and | |
1511 | displaying eight-bit characters. You use readline variables to do | |
1512 | this. These variables can be set in your .inputrc or using the bash | |
1513 | `bind' builtin. Here's an example using `bind': | |
1514 | ||
1515 | bash$ bind 'set convert-meta off' | |
1516 | bash$ bind 'set meta-flag on' | |
1517 | bash$ bind 'set output-meta on' | |
1518 | ||
1519 | The `set' commands between the single quotes may also be placed | |
1520 | in ~/.inputrc. | |
1521 | ||
1522 | G2) How do I write a function `x' to replace builtin command `x', but | |
1523 | still invoke the command from within the function? | |
1524 | ||
1525 | This is why the `command' and `builtin' builtins exist. The | |
1526 | `command' builtin executes the command supplied as its first | |
1527 | argument, skipping over any function defined with that name. The | |
1528 | `builtin' builtin executes the builtin command given as its first | |
1529 | argument directly. | |
1530 | ||
1531 | For example, to write a function to replace `cd' that writes the | |
1532 | hostname and current directory to an xterm title bar, use | |
1533 | something like the following: | |
1534 | ||
1535 | cd() | |
1536 | { | |
1537 | builtin cd "$@" && xtitle "$HOST: $PWD" | |
1538 | } | |
1539 | ||
1540 | This could also be written using `command' instead of `builtin'; | |
1541 | the version above is marginally more efficient. | |
1542 | ||
1543 | G3) How can I find the value of a shell variable whose name is the value | |
1544 | of another shell variable? | |
1545 | ||
1546 | Versions of Bash newer than Bash-2.0 support this directly. You can use | |
1547 | ||
1548 | ${!var} | |
1549 | ||
1550 | For example, the following sequence of commands will echo `z': | |
1551 | ||
1552 | var1=var2 | |
1553 | var2=z | |
1554 | echo ${!var1} | |
1555 | ||
1556 | For sh compatibility, use the `eval' builtin. The important | |
1557 | thing to remember is that `eval' expands the arguments you give | |
1558 | it again, so you need to quote the parts of the arguments that | |
1559 | you want `eval' to act on. | |
1560 | ||
1561 | For example, this expression prints the value of the last positional | |
1562 | parameter: | |
1563 | ||
1564 | eval echo \"\$\{$#\}\" | |
1565 | ||
1566 | The expansion of the quoted portions of this expression will be | |
1567 | deferred until `eval' runs, while the `$#' will be expanded | |
1568 | before `eval' is executed. In versions of bash later than bash-2.0, | |
1569 | ||
1570 | echo ${!#} | |
1571 | ||
1572 | does the same thing. | |
1573 | ||
1574 | This is not the same thing as ksh93 `nameref' variables, though the syntax | |
1575 | is similar. I may add namerefs in a future bash version. | |
1576 | ||
1577 | G4) How can I make the bash `time' reserved word print timing output that | |
1578 | looks like the output from my system's /usr/bin/time? | |
1579 | ||
1580 | The bash command timing code looks for a variable `TIMEFORMAT' and | |
1581 | uses its value as a format string to decide how to display the | |
1582 | timing statistics. | |
1583 | ||
1584 | The value of TIMEFORMAT is a string with `%' escapes expanded in a | |
1585 | fashion similar in spirit to printf(3). The manual page explains | |
1586 | the meanings of the escape sequences in the format string. | |
1587 | ||
1588 | If TIMEFORMAT is not set, bash acts as if the following assignment had | |
1589 | been performed: | |
1590 | ||
1591 | TIMEFORMAT=$'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS' | |
1592 | ||
1593 | The POSIX.2 default time format (used by `time -p command') is | |
1594 | ||
1595 | TIMEFORMAT=$'real %2R\nuser %2U\nsys %2S' | |
1596 | ||
1597 | The BSD /usr/bin/time format can be emulated with: | |
1598 | ||
1599 | TIMEFORMAT=$'\t%1R real\t%1U user\t%1S sys' | |
1600 | ||
1601 | The System V /usr/bin/time format can be emulated with: | |
1602 | ||
1603 | TIMEFORMAT=$'\nreal\t%1R\nuser\t%1U\nsys\t%1S' | |
1604 | ||
1605 | The ksh format can be emulated with: | |
1606 | ||
1607 | TIMEFORMAT=$'\nreal\t%2lR\nuser\t%2lU\nsys\t%2lS' | |
1608 | ||
1609 | G5) How do I get the current directory into my prompt? | |
1610 | ||
1611 | Bash provides a number of backslash-escape sequences which are expanded | |
1612 | when the prompt string (PS1 or PS2) is displayed. The full list is in | |
1613 | the manual page. | |
1614 | ||
1615 | The \w expansion gives the full pathname of the current directory, with | |
1616 | a tilde (`~') substituted for the current value of $HOME. The \W | |
1617 | expansion gives the basename of the current directory. To put the full | |
1618 | pathname of the current directory into the path without any tilde | |
1619 | subsitution, use $PWD. Here are some examples: | |
1620 | ||
1621 | PS1='\w$ ' # current directory with tilde | |
1622 | PS1='\W$ ' # basename of current directory | |
1623 | PS1='$PWD$ ' # full pathname of current directory | |
1624 | ||
1625 | The single quotes are important in the final example to prevent $PWD from | |
1626 | being expanded when the assignment to PS1 is performed. | |
1627 | ||
1628 | G6) How can I rename "*.foo" to "*.bar"? | |
1629 | ||
1630 | Use the pattern removal functionality described in D3. The following `for' | |
1631 | loop will do the trick: | |
1632 | ||
1633 | for f in *.foo; do | |
1634 | mv $f ${f%foo}bar | |
1635 | done | |
1636 | ||
1637 | G7) How can I translate a filename from uppercase to lowercase? | |
1638 | ||
1639 | The script examples/functions/lowercase, originally written by John DuBois, | |
1640 | will do the trick. The converse is left as an exercise. | |
1641 | ||
1642 | G8) How can I write a filename expansion (globbing) pattern that will match | |
1643 | all files in the current directory except "." and ".."? | |
1644 | ||
1645 | You must have set the `extglob' shell option using `shopt -s extglob' to use | |
1646 | this: | |
1647 | ||
1648 | echo .!(.|) * | |
1649 | ||
1650 | A solution that works without extended globbing is given in the Unix Shell | |
1651 | FAQ, posted periodically to comp.unix.shell. | |
1652 | ||
1653 | Section H: Where do I go from here? | |
1654 | ||
1655 | H1) How do I report bugs in bash, and where should I look for fixes and | |
1656 | advice? | |
1657 | ||
1658 | Use the `bashbug' script to report bugs. It is built and | |
1659 | installed at the same time as bash. It provides a standard | |
1660 | template for reporting a problem and automatically includes | |
1661 | information about your configuration and build environment. | |
1662 | ||
1663 | `bashbug' sends its reports to bug-bash@gnu.org, which | |
1664 | is a large mailing list gatewayed to the usenet newsgroup gnu.bash.bug. | |
1665 | ||
1666 | Bug fixes, answers to questions, and announcements of new releases | |
1667 | are all posted to gnu.bash.bug. Discussions concerning bash features | |
1668 | and problems also take place there. | |
1669 | ||
1670 | To reach the bash maintainers directly, send mail to | |
1671 | bash-maintainers@gnu.org. | |
1672 | ||
1673 | H2) What kind of bash documentation is there? | |
1674 | ||
1675 | First, look in the doc directory in the bash distribution. It should | |
1676 | contain at least the following files: | |
1677 | ||
1678 | bash.1 an extensive, thorough Unix-style manual page | |
1679 | builtins.1 a manual page covering just bash builtin commands | |
1680 | bashref.texi a reference manual in GNU tex`info format | |
1681 | bashref.info an info version of the reference manual | |
1682 | FAQ this file | |
1683 | article.ms text of an article written for The Linux Journal | |
1684 | readline.3 a man page describing readline | |
1685 | ||
1686 | Postscript, HTML, and ASCII files created from the above source are | |
1687 | available in the documentation distribution. | |
1688 | ||
1689 | There is additional documentation available for anonymous FTP from host | |
1690 | ftp.cwru.edu in the `pub/bash' directory. | |
1691 | ||
1692 | Cameron Newham and Bill Rosenblatt have written a book on bash, published | |
1693 | by O'Reilly and Associates. The book is based on Bill Rosenblatt's Korn | |
1694 | Shell book. The title is ``Learning the Bash Shell'', and the ISBN number | |
1695 | is 1-56592-147-X. Look for it in fine bookstores near you. This book | |
1696 | covers bash-1.14, but has an appendix describing some of the new features | |
1697 | in bash-2.0. | |
1698 | ||
1699 | A second edition of this book is available, published in January, 1998. | |
1700 | The ISBN number is 1-56592-347-2. Look for it in the same fine bookstores | |
1701 | or on the web. | |
1702 | ||
1703 | The GNU Bash Reference Manual has been published as a printed book by | |
1704 | Network Theory Ltd (Paperback, ISBN: 0-9541617-7-7, Feb 2003). It covers | |
1705 | bash-2.0 and is available from most online bookstores (see | |
1706 | http://www.network-theory.co.uk/bash/manual/ for details). The publisher | |
1707 | will donate $1 to the Free Software Foundation for each copy sold. | |
1708 | ||
1709 | H3) What's coming in future versions? | |
1710 | ||
1711 | These are features I hope to include in a future version of bash. | |
1712 | ||
1713 | a better bash debugger (a minimally-tested version is included with bash-2.05b) | |
1714 | associative arrays | |
1715 | co-processes, but with a new-style syntax that looks like function declaration | |
1716 | ||
1717 | H4) What's on the bash `wish list' for future versions? | |
1718 | ||
1719 | These are features that may or may not appear in a future version of bash. | |
1720 | ||
1721 | breaking some of the shell functionality into embeddable libraries | |
1722 | a module system like zsh's, using dynamic loading like builtins | |
1723 | better internationalization using GNU `gettext' | |
1724 | date-stamped command history | |
1725 | a bash programmer's guide with a chapter on creating loadable builtins | |
1726 | a better loadable interface to perl with access to the shell builtins and | |
1727 | variables (contributions gratefully accepted) | |
1728 | ksh93-like `nameref' variables | |
1729 | ksh93-like `+=' variable assignment operator | |
1730 | ksh93-like `xx.yy' variables (including some of the .sh.* variables) and | |
1731 | associated disipline functions | |
1732 | Some of the new ksh93 pattern matching operators, like backreferencing | |
1733 | ||
1734 | H5) When will the next release appear? | |
1735 | ||
1736 | The next version will appear sometime in 2002. Never make predictions. | |
1737 | ||
1738 | ||
1739 | This document is Copyright 1995-2003 by Chester Ramey. | |
1740 | ||
1741 | Permission is hereby granted, without written agreement and | |
1742 | without license or royalty fees, to use, copy, and distribute | |
1743 | this document for any purpose, provided that the above copyright | |
1744 | notice appears in all copies of this document and that the | |
1745 | contents of this document remain unaltered. |