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d166f048 | 1 | This is the Bash FAQ, version 2.5, for Bash version 2.01. |
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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://slc2.ins.cwru.edu/pub/bash/FAQ | |
17 | ||
18 | ---------- | |
19 | Contents: | |
20 | ||
21 | Section A: The Basics | |
22 | ||
23 | 1) What is it? | |
24 | 2) What's the latest version? | |
25 | 3) Where can I get it? | |
26 | 4) On what machines will bash run? | |
d166f048 JA |
27 | 5) Will bash run on operating systems other than Unix? |
28 | 6) How can I build bash with gcc? | |
29 | 7) How can I make bash my login shell? | |
30 | 8) I just changed my login shell to bash, and now I can't FTP into my | |
ccc6cda3 | 31 | machine. Why not? |
d166f048 JA |
32 | 9) What's the `POSIX 1003.2 standard'? |
33 | 10) What is the bash `posix mode'? | |
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34 | |
35 | Section B: The latest version | |
36 | ||
d166f048 JA |
37 | 11) What's new in version 2.01? |
38 | 12) Are there any user-visible incompatibilities between bash-2.01 and | |
ccc6cda3 JA |
39 | bash-1.14.7? |
40 | ||
41 | Section C: Differences from other Unix shells | |
42 | ||
d166f048 JA |
43 | 13) How does bash differ from sh, the Bourne shell? |
44 | 14) How does bash differ from the Korn shell, version ksh88? | |
45 | 15) Which new features in ksh-93 are not in bash, and which are? | |
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46 | |
47 | Section D: Why does bash do some things differently than other Unix shells? | |
48 | ||
d166f048 | 49 | 16) Why does bash run a different version of `command' than |
ccc6cda3 | 50 | `which command' says it will? |
d166f048 JA |
51 | 17) Why doesn't bash treat brace expansions exactly like csh? |
52 | 18) Why doesn't bash have csh variable modifiers? | |
53 | 19) How can I make my csh aliases work when I convert to bash? | |
54 | 20) How can I pipe standard output and standard error from one command to | |
ccc6cda3 | 55 | another, like csh does with `|&'? |
d166f048 | 56 | 21) Now that I've converted from ksh to bash, are there equivalents to |
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57 | ksh features like autoloaded functions and the `whence' command? |
58 | ||
59 | Section E: How can I get bash to do certain things, and why does bash do | |
60 | things the way it does? | |
61 | ||
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62 | 22) Why is the bash builtin `test' slightly different from /bin/test? |
63 | 23) Why does bash sometimes say `Broken pipe'? | |
64 | 24) How can I get bash to read and display eight-bit characters? | |
65 | 25) How do I write a function `x' to replace builtin command `x', but | |
ccc6cda3 | 66 | still invoke the command from within the function? |
d166f048 | 67 | 26) When I have terminal escape sequences in my prompt, why does bash |
ccc6cda3 | 68 | wrap lines at the wrong column? |
d166f048 | 69 | 27) How can I find the value of a shell variable whose name is the value |
ccc6cda3 | 70 | of another shell variable? |
d166f048 | 71 | 28) If I pipe the output of a command into `read variable', why doesn't |
ccc6cda3 | 72 | the output show up in $variable when the read command finishes? |
d166f048 | 73 | 29) I have a bunch of shell scripts that use backslash-escaped characters |
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74 | in arguments to `echo'. Bash doesn't interpret these characters. Why |
75 | not, and how can I make it understand them? | |
d166f048 JA |
76 | 30) Why doesn't a while or for loop get suspended when I type ^Z? |
77 | 31) How can I make the bash `time' reserved word print timing output that | |
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78 | looks like the output from my system's /usr/bin/time? |
79 | ||
80 | Section F: Things to watch out for on certain Unix versions | |
81 | ||
d166f048 JA |
82 | 32) Why can't I use command line editing in my `cmdtool'? |
83 | 33) I built bash on Solaris 2. Why do globbing expansions and filename | |
ccc6cda3 | 84 | completion chop off the first few characters of each filename? |
d166f048 | 85 | 34) Why does bash dump core after I interrupt username completion or |
ccc6cda3 | 86 | `~user' tilde expansion on a machine running NIS? |
d166f048 JA |
87 | 35) I'm running SVR4.2. Why is the line erased every time I type `@'? |
88 | 36) Why does bash report syntax errors when my C News scripts use a | |
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89 | redirection before a subshell command? |
90 | ||
91 | Section G: Where do I go from here? | |
92 | ||
d166f048 | 93 | 37) How do I report bugs in bash, and where should I look for fixes and |
ccc6cda3 | 94 | advice? |
d166f048 JA |
95 | 38) What kind of bash documentation is there? |
96 | 39) What's coming in future versions? | |
97 | 40) What's on the bash `wish list'? | |
98 | 41) When will the next release appear? | |
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99 | |
100 | ---------- | |
101 | Section A: The Basics | |
102 | ||
103 | 1) What is it? | |
104 | ||
105 | Bash is a Unix command interpreter (shell). It is an implementation of | |
106 | the Posix 1003.2 shell standard, and resembles the Korn and System V | |
107 | shells. | |
108 | ||
109 | Bash contains a number of enhancements over those shells, both | |
110 | for interactive use and shell programming. Features geared | |
111 | toward interactive use include command line editing, command | |
112 | history, job control, aliases, and prompt expansion. Programming | |
113 | features include additional variable expansions, shell | |
114 | arithmetic, and a number of variables and options to control | |
115 | shell behavior. | |
116 | ||
117 | Bash was originally written by Brian Fox of the Free Software | |
118 | Foundation. The current developer and maintainer is Chet Ramey | |
119 | of Case Western Reserve University. | |
120 | ||
121 | 2) What's the latest version? | |
122 | ||
d166f048 | 123 | The latest version is 2.01, first made available on June 6, 1997. |
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124 | |
125 | 3) Where can I get it? | |
126 | ||
127 | Bash is the GNU project's shell, and so is available from the | |
128 | master GNU archive site, prep.ai.mit.edu, and its mirrors. The | |
129 | latest version is also available for FTP from slc2.ins.cwru.edu, | |
130 | the maintainer's machine. The following URLs tell how to get | |
d166f048 | 131 | version 2.01: |
ccc6cda3 | 132 | |
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133 | ftp://prep.ai.mit.edu/pub/gnu/bash-2.01.tar.gz |
134 | ftp://slc2.ins.cwru.edu/pub/dist/bash-2.01.tar.gz | |
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135 | |
136 | Formatted versions of the documentation are available with the URLs: | |
137 | ||
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138 | ftp://prep.ai.mit.edu/pub/gnu/bash-doc-2.01.tar.gz |
139 | ftp://slc2.ins.cwru.edu/pub/dist/bash-doc-2.01.tar.gz | |
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140 | |
141 | 4) On what machines will bash run? | |
142 | ||
143 | Bash has been ported to nearly every version of UNIX. All you | |
144 | should have to do to build it on a machine for which a port | |
145 | exists is to type `configure' and then `make'. The build process | |
146 | will attempt to discover the version of UNIX you have and tailor | |
147 | itself accordingly, using a script created by GNU autoconf. | |
148 | ||
149 | More information appears in the file `INSTALL' in the distribution. | |
150 | ||
d166f048 JA |
151 | 5) Will bash run on operating systems other than Unix? |
152 | ||
153 | Configuration specifics for Unix-like systems such as QNX and | |
154 | LynxOS are included in the distribution. Previous versions of | |
155 | bash have been ported to Minix, but I don't believe anyone has | |
156 | built bash-2.x on Minix yet. | |
157 | ||
158 | Bash has been ported to versions of Windows implementing the Win32 | |
159 | programming interface. This includes Windows 95 and Windows NT. | |
160 | The port was done by Cygnus Solutions as part of their GNU-Win32 | |
161 | project. For more information about the project, look at the URL | |
162 | ||
163 | http://www.cygnus.com/misc/gnu-win32 | |
164 | ||
165 | Cygnus has ported bash-1.14.7. Maybe someday they (or I) will port | |
166 | bash-2.01 (or later) to the GNU-Win32 environment. | |
167 | ||
168 | D. J. Delorie has ported bash-1.14.7 to run under MS-DOS, as part of | |
169 | the DJGPP project. For more information on the project, see | |
170 | ||
171 | http://www.delorie.com/djgpp/ | |
172 | ||
173 | I picked up a binary of bash-1.14.7 that is purported to work with | |
174 | the DJGPP V2 environment from | |
175 | ||
176 | ftp://ftp.simtel.net/pub/simtelnet/gnu/djgpp/v2gnu/bsh1147b.zip | |
177 | ||
178 | The corresponding source is | |
179 | ||
180 | ftp://ftp.simtel.net/pub/simtelnet/gnu/djgpp/v2gnu/bsh1147s.zip | |
181 | ||
182 | A port of bash-1.12 is available for OS/2 from | |
183 | ||
184 | ftp://hobbes.nmsu.edu/os2/unix/bash_112.zip | |
185 | ||
186 | I haven't looked at it. | |
187 | ||
188 | 6) How can I build bash with gcc? | |
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189 | |
190 | Bash configures to use gcc by default if it is available. Read the | |
191 | file INSTALL in the distribution for more information. | |
192 | ||
d166f048 | 193 | 7) How can I make bash my login shell? |
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194 | |
195 | Some machines let you use `chsh' to change your login shell. Other | |
196 | systems use `passwd -s'. If one of these works for you, that's all | |
197 | you need. Note that many systems require the full pathname to a shell | |
198 | to appear in /etc/shells before you can make it your login shell. For | |
199 | this, you may need the assistance of your friendly local system | |
200 | administrator. | |
201 | ||
202 | If you cannot do this, you can still use bash as your login shell, but | |
203 | you need to perform some tricks. The basic idea is to add a command | |
204 | to your login shell's startup file to replace your login shell with | |
205 | bash. | |
206 | ||
207 | For example, if your login shell is csh or tcsh, and you have installed | |
208 | bash in /usr/gnu/bin/bash, add the following line to ~/.login: | |
209 | ||
210 | if ( -f /usr/gnu/bin/bash ) exec /usr/gnu/bin/bash --login | |
211 | ||
212 | (the `--login' tells bash that it is a login shell). | |
213 | ||
214 | It's not a good idea to put this command into ~/.cshrc, because every | |
215 | csh you run without the `-f' option, even ones started to run csh scripts, | |
216 | reads that file. If you must put the command in ~/.cshrc, use something | |
217 | like | |
218 | ||
219 | if ( $?prompt ) exec /usr/gnu/bin/bash --login | |
220 | ||
221 | to ensure that bash is exec'd only when the csh is interactive. | |
222 | ||
d166f048 | 223 | If your login shell is sh or ksh, you have to do two things. |
ccc6cda3 | 224 | |
d166f048 | 225 | First, create an empty file in your home directory named `.bash_profile'. |
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226 | The existence of this file will prevent the exec'd bash from trying to |
227 | read ~/.profile, and re-execing itself over and over again. ~/.bash_profile | |
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228 | is the first file bash tries to read initialization commands from when |
229 | it is invoked as a login shell. | |
230 | ||
231 | Next, add a line similar to the above to ~/.profile: | |
232 | ||
233 | [ -f /usr/gnu/bin/bash ] && exec /usr/gnu/bin/bash --login | |
ccc6cda3 | 234 | |
d166f048 JA |
235 | This will cause login shells to replace themselves with bash running as |
236 | a login shell. Once you have this working, you can copy your initialization | |
237 | code from ~/.profile to ~/.bash_profile. | |
238 | ||
239 | 8) I just changed my login shell to bash, and now I can't FTP into my | |
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240 | machine. Why not? |
241 | ||
242 | You must add the full pathname to bash to the file /etc/shells. As | |
243 | noted in the answer to the previous question, many systems require | |
244 | this before you can make bash your login shell. | |
245 | ||
246 | Most versions of ftpd use this file to prohibit `special' users | |
247 | such as `uucp' and `news' from using FTP. | |
248 | ||
d166f048 | 249 | 9) What's the `POSIX 1003.2 standard'? |
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250 | |
251 | POSIX is a name originally coined by Richard Stallman for a | |
252 | family of open system standards based on UNIX. There are a | |
253 | number of aspects of UNIX under consideration for | |
254 | standardization, from the basic system services at the system | |
255 | call and C library level to applications and tools to system | |
256 | administration and management. Each area of standardization is | |
257 | assigned to a working group in the 1003 series. | |
258 | ||
259 | The POSIX Shell and Utilities standard has been developed by IEEE | |
260 | Working Group 1003.2 (POSIX.2). It concentrates on the command | |
261 | interpreter interface and utility programs commonly executed from | |
262 | the command line or by other programs. An initial version of the | |
263 | standard has been approved and published by the IEEE, and work is | |
264 | currently underway to update it. | |
265 | ||
266 | Bash is concerned with the aspects of the shell's behavior | |
267 | defined by POSIX.2. The shell command language has of course | |
268 | been standardized, including the basic flow control and program | |
269 | execution constructs, I/O redirection and pipelining, argument | |
270 | handling, variable expansion, and quoting. | |
271 | ||
272 | The `special' builtins, which must be implemented as part of the | |
273 | shell to provide the desired functionality, are specified as | |
274 | being part of the shell; examples of these are `eval' and | |
275 | `export'. Other utilities appear in the sections of POSIX.2 not | |
276 | devoted to the shell which are commonly (and in some cases must | |
277 | be) implemented as builtin commands, such as `read' and `test'. | |
278 | POSIX.2 also specifies aspects of the shell's interactive | |
279 | behavior as part of the UPE, including job control and command | |
280 | line editing. Only vi-style line editing commands have been | |
281 | standardized; emacs editing commands were left out due to | |
282 | objections. | |
283 | ||
d166f048 | 284 | 10) What is the bash `posix mode'? |
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285 | |
286 | Although bash is an implementation of the POSIX.2 shell | |
287 | specification, there are areas where the bash default behavior | |
288 | differs from that spec. The bash `posix mode' changes the bash | |
289 | behavior in these areas so that it obeys the spec more closely. | |
290 | ||
291 | Posix mode is entered by starting bash with the --posix option or | |
292 | executing `set -o posix' after bash is running. | |
293 | ||
294 | The specific aspects of bash which change when posix mode is | |
295 | active are listed in the file CWRU/POSIX.NOTES in the bash | |
296 | distribution. They are also listed in a section in the Bash | |
297 | Reference Manual. | |
298 | ||
299 | Section B: The latest version | |
300 | ||
d166f048 JA |
301 | 11) What's new in version 2.01? |
302 | ||
303 | Bash-2.01 contains only a few new features. | |
304 | ||
305 | new `GROUPS' builtin array variable containing the user's group list | |
306 | new bindable readline commands: history-and-alias-expand-line and | |
307 | alias-expand-line | |
ccc6cda3 | 308 | |
d166f048 JA |
309 | Bash-2.0 contains extensive changes and new features from bash-1.14.7. |
310 | Here's a short list: | |
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311 | |
312 | new `time' reserved word to time pipelines, shell builtins, and | |
313 | shell functions | |
314 | one-dimensional arrays with a new compound assignment statement, | |
315 | appropriate expansion constructs and modifications to some | |
316 | of the builtins (read, declare, etc.) to use them | |
317 | new quoting syntaxes for ANSI-C string expansion and locale-specific | |
318 | string translation | |
319 | new expansions to do substring extraction, pattern replacement, and | |
320 | indirect variable expansion | |
321 | new builtins: `disown' and `shopt' | |
322 | new variables: HISTIGNORE, SHELLOPTS, PIPESTATUS, DIRSTACK, GLOBIGNORE, | |
323 | MACHTYPE, BASH_VERSINFO | |
324 | special handling of many unused or redundant variables removed | |
325 | (e.g., $notify, $glob_dot_filenames, $no_exit_on_failed_exec) | |
326 | dynamic loading of new builtin commands; many loadable examples provided | |
327 | new prompt expansions: \a, \e, \n, \H, \T, \@, \v, \V | |
328 | history and aliases available in shell scripts | |
329 | new readline variables: enable-keypad, mark-directories, input-meta, | |
330 | visible-stats, disable-completion, comment-begin | |
331 | new readline commands to manipulate the mark and operate on the region | |
332 | new readline emacs mode commands and bindings for ksh-88 compatibility | |
333 | updated and extended builtins | |
334 | new DEBUG trap | |
335 | expanded (and now documented) restricted shell mode | |
336 | ||
337 | implementation stuff: | |
338 | autoconf-based configuration | |
339 | nearly all of the bugs reported since version 1.14 have been fixed | |
340 | most builtins converted to use builtin `getopt' for consistency | |
341 | most builtins use -p option to display output in a reusable form | |
342 | (for consistency) | |
343 | grammar tighter and smaller (66 reduce-reduce conflicts gone) | |
344 | lots of code now smaller and faster | |
345 | test suite greatly expanded | |
346 | ||
d166f048 | 347 | 12) Are there any user-visible incompatibilities between bash-2.01 and |
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348 | bash-1.14.7? |
349 | ||
d166f048 JA |
350 | There are a few incompatibilities between version 1.14.7 and version 2.01. |
351 | They are detailed in the file COMPAT in the bash-2.01 distribution. | |
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352 | |
353 | Section C: Differences from other Unix shells | |
354 | ||
d166f048 | 355 | 13) How does bash differ from sh, the Bourne shell? |
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356 | |
357 | This is a non-comprehensive list of features that differentiate bash | |
358 | from the SVR4.2 shell. The bash manual page explains these more | |
359 | completely. | |
360 | ||
361 | Things bash has that sh does not: | |
362 | long invocation options | |
363 | `!' reserved word to invert pipeline return value | |
364 | `time' reserved word to time pipelines and shell builtins | |
365 | the `function' reserved word | |
366 | the select compound command and reserved word | |
367 | new $'...' and $"..." quoting | |
368 | the $(...) form of command substitution | |
369 | the ${#param} parameter value length operator | |
370 | the ${!param} indirect parameter expansion operator | |
371 | the ${param:length[:offset]} parameter substring operator | |
372 | the ${param/pat[/string]} parameter pattern substitution operator | |
373 | expansions to perform substring removal (${p%[%]w}, ${p#[#]w}) | |
374 | expansion of positional parameters beyond $9 with ${num} | |
375 | variables: BASH, BASH_VERSION, BASH_VERSINFO, UID, EUID, REPLY, | |
376 | TIMEFORMAT, PPID, PWD, OLDPWD, SHLVL, RANDOM, SECONDS, | |
377 | LINENO, HISTCMD, HOSTTYPE, OSTYPE, MACHTYPE, HOSTNAME, | |
378 | ENV, PS3, PS4, DIRSTACK, PIPESTATUS, HISTSIZE, HISTFILE, | |
379 | HISTFILESIZE, HISTCONTROL, HISTIGNORE, GLOBIGNORE, | |
380 | PROMPT_COMMAND, FCEDIT, FIGNORE, IGNOREEOF, INPUTRC, | |
381 | SHELLOPTS, OPTERR, HOSTFILE, TMOUT, histchars, auto_resume | |
382 | DEBUG trap | |
383 | variable arrays with new compound assignment syntax | |
384 | redirections: <>, &>, >| | |
385 | prompt string special char translation and variable expansion | |
386 | auto-export of modified values of variables in initial environment | |
387 | command search finds functions before builtins | |
388 | bash return builtin will exit a file sourced with `.' | |
389 | builtins: cd -/-L/-P, exec -l/-c/-a, echo -e/-E, hash -p. | |
390 | export -n/-f/-p/name=value, pwd -L/-P, read -e/-p/-a, | |
391 | readonly -a/-f/name=value, trap -l, set +o, | |
392 | set -b/-m/-o option/-h/-p/-B/-C/-H/-P, | |
393 | unset -f/-v, ulimit -m/-p/-u, | |
394 | type -a/-p/-t, suspend -f, kill -n, | |
395 | test -o optname/s1 == s2/s1 < s2/s1 > s2/-nt/-ot/-ef/-O/-G/-S | |
396 | bash reads ~/.bashrc for interactive shells, $ENV for non-interactive | |
397 | bash restricted shell mode is more extensive | |
398 | bash allows functions and variables with the same name | |
399 | brace expansion | |
400 | tilde expansion | |
401 | arithmetic expansion with $((...)) and `let' builtin | |
402 | process substitution | |
403 | aliases and alias/unalias builtins | |
404 | local variables in functions and `local' builtin | |
405 | readline and command-line editing | |
406 | command history and history/fc builtins | |
407 | csh-like history expansion | |
408 | other new bash builtins: bind, command, builtin, declare/typeset, | |
409 | dirs, enable, fc, help, history, logout, | |
410 | popd, pushd, disown, shopt | |
411 | exported functions | |
412 | filename generation when using output redirection (command >a*) | |
413 | variable assignments preceding commands affect only that command, | |
414 | even for builtins and functions | |
415 | posix mode | |
416 | ||
417 | Things sh has that bash does not: | |
418 | uses variable SHACCT to do shell accounting | |
419 | includes `stop' builtin (bash can use alias stop='kill -s STOP') | |
420 | `newgrp' builtin | |
421 | turns on job control if called as `jsh' | |
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422 | $TIMEOUT (like bash $TMOUT) |
423 | `^' is a synonym for `|' | |
424 | new SVR4.2 sh builtins: mldmode, priv | |
425 | ||
426 | Implementation differences: | |
427 | redirection to/from compound commands causes sh to create a subshell | |
428 | bash does not allow unbalanced quotes; sh silently inserts them at EOF | |
429 | bash does not mess with signal 11 | |
430 | sh sets (euid, egid) to (uid, gid) if -p not supplied and uid < 100 | |
431 | bash splits only the results of expansions on IFS, using POSIX.2 | |
432 | field splitting rules; sh splits all words on IFS | |
433 | sh does not allow MAILCHECK to be unset (?) | |
434 | sh does not allow traps on SIGALRM or SIGCHLD | |
435 | bash allows multiple option arguments when invoked (e.g. -x -v); | |
436 | sh allows only a single option argument (`sh -x -v' attempts | |
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437 | to open a file named `-v', and, on SunOS 4.1.4, dumps core. |
438 | On Solaris 2, sh goes into an infinite loop.) | |
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439 | sh exits a script if any builtin fails; bash exits only if one of |
440 | the POSIX.2 `special' builtins fails | |
441 | ||
d166f048 | 442 | 14) How does bash differ from the Korn shell, version ksh88? |
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443 | |
444 | Things bash has or uses that ksh88 does not: | |
445 | long invocation options | |
446 | `!' reserved word | |
447 | posix mode and posix conformance | |
448 | command hashing | |
449 | tilde expansion for assignment statements that look like $PATH | |
450 | process substitution with named pipes if /dev/fd is not available | |
451 | the ${!param} indirect parameter expansion operator | |
452 | the ${param:length[:offset]} parameter substring operator | |
453 | the ${param/pat[/string]} parameter pattern substitution operator | |
454 | variables: BASH, BASH_VERSION, BASH_VERSINFO, UID, EUID, SHLVL, | |
455 | TIMEFORMAT, HISTCMD, HOSTTYPE, OSTYPE, MACHTYPE, | |
456 | HISTFILESIZE, HISTIGNORE, HISTCONTROL, PROMPT_COMMAND, | |
457 | IGNOREEOF, FIGNORE, INPUTRC, HOSTFILE, DIRSTACK, | |
458 | PIPESTATUS, HOSTNAME, OPTERR, SHELLOPTS, GLOBIGNORE, | |
459 | histchars, auto_resume | |
460 | prompt expansion with backslash escapes and command substitution | |
461 | redirection: &> (stdout and stderr) | |
462 | more extensive and extensible editing and completion | |
463 | builtins: bind, builtin, command, declare, dirs, echo -e/-E, enable, | |
464 | exec -l/-c/-a, fc -s, export -n/-f/-p, hash, help, history, | |
465 | jobs -x/-r/-s, kill -s/-n/-l, local, logout, popd, pushd, | |
466 | read -e/-p/-a, readonly -a/-n/-f/-p, set -o braceexpand/ | |
467 | -o histexpand/-o interactive-comments/-o notify/-o physical/ | |
468 | -o posix/-o hashall/-o onecmd/-h/-B/-C/-b/-H/-P, set +o, | |
469 | suspend, trap -l, type, typeset -a/-F/-p, ulimit -u, | |
470 | umask -S, alias -p, shopt, disown | |
471 | `!' csh-style history expansion | |
472 | ||
473 | Things ksh88 has or uses that bash does not: | |
474 | new version of test: [[...]] | |
475 | tracked aliases | |
476 | $(<file) | |
477 | variables: ERRNO, FPATH, COLUMNS, LINES, EDITOR, VISUAL | |
478 | extended pattern matching with egrep-style pattern lists | |
479 | co-processes (|&, >&p, <&p) | |
480 | weirdly-scoped functions | |
481 | typeset +f to list all function names without definitions | |
482 | text of command history kept in a file, not memory | |
483 | builtins: alias -x, cd old new, fc -e -, newgrp, print, | |
484 | read -p/-s/-u/var?prompt, set -A/-o gmacs/ | |
485 | -o bgnice/-o markdirs/-o nolog/-o trackall/-o viraw/-s, | |
486 | typeset -H/-L/-R/-A/-ft/-fu/-fx/-l/-u/-t, whence | |
487 | ||
488 | Implementation differences: | |
489 | ksh runs last command of a pipeline in parent shell context | |
ccc6cda3 JA |
490 | bash has brace expansion by default (ksh88 compile-time option) |
491 | bash has fixed startup file for all interactive shells; ksh reads $ENV | |
492 | bash has exported functions | |
493 | bash command search finds functions before builtins | |
494 | ||
d166f048 | 495 | 15) Which new features in ksh-93 are not in bash, and which are? |
ccc6cda3 | 496 | |
d166f048 | 497 | New things in ksh-93 not in bash-2.01: |
ccc6cda3 JA |
498 | associative arrays |
499 | floating point arithmetic | |
500 | ++, --, comma arithmetic operators | |
501 | math library functions | |
502 | ${!name[sub]} name of subscript for associative array | |
503 | ${!prefix*} and {!prefix@} variable name prefix expansions | |
504 | `.' is allowed in variable names to create a hierarchical namespace | |
505 | more extensive compound assignment syntax | |
506 | discipline functions | |
507 | `sleep' and `getconf' builtins (bash has loadable versions) | |
508 | typeset -n and `nameref' variables | |
509 | KEYBD trap | |
510 | variables: .sh.edchar, .sh.edmode, .sh.edcol, .sh.edtext, HISTEDIT, | |
511 | .sh.version, .sh.name, .sh.subscript, .sh.value | |
512 | backreferences in pattern matching | |
513 | print -f and printf (bash has loadable versions) | |
514 | `fc' has been renamed to `hist' | |
515 | read -t/-d | |
516 | `.' can execute shell functions | |
ccc6cda3 | 517 | |
d166f048 | 518 | New things in ksh-93 present in bash-2.01: |
ccc6cda3 | 519 | ?: arithmetic operator |
d166f048 | 520 | expansions: ${!param}, ${param:offset[:len]}, ${param/pat[/str]} |
ccc6cda3 JA |
521 | compound array assignment |
522 | the `!' reserved word | |
523 | loadable builtins -- but ksh uses `builtin' while bash uses `enable' | |
524 | `command', `builtin', `disown' builtins | |
525 | new $'...' and $"..." quoting | |
526 | FIGNORE (but bash uses GLOBIGNORE), HISTCMD | |
527 | set -o notify/-C | |
528 | changes to kill builtin | |
529 | read -A (bash uses read -a) | |
530 | trap -p | |
531 | exec -c/-a | |
532 | `.' restores the positional parameters when it completes | |
533 | POSIX.2 `test' | |
534 | umask -S | |
535 | unalias -a | |
536 | command and arithmetic substitution performed on PS1, PS4, and ENV | |
537 | command name completion | |
d166f048 | 538 | ENV processed only for interactive shells |
ccc6cda3 JA |
539 | |
540 | Section D: Why does bash do some things differently than other Unix shells? | |
541 | ||
d166f048 | 542 | 16) Why does bash run a different version of `command' than |
ccc6cda3 JA |
543 | `which command' says it will? |
544 | ||
545 | `which' is actually a csh script that assumes you're running csh. | |
546 | It reads the csh startup files from your home directory and uses | |
547 | those to determine which `command' will be invoked. Since bash | |
548 | doesn't use any of those startup files, there's a good chance | |
549 | that your bash environment differs from your csh environment. | |
550 | ||
d166f048 | 551 | 17) Why doesn't bash treat brace expansions exactly like csh? |
ccc6cda3 JA |
552 | |
553 | The only difference between bash and csh brace expansion is that | |
554 | bash requires a brace expression to contain at least one unquoted | |
555 | comma if it is to be expanded. Any brace-surrounded word not | |
556 | containing an unquoted comma is left unchanged by the brace | |
557 | expansion code. This affords the greatest degree of sh | |
558 | compatibility. | |
559 | ||
560 | Bash, ksh, zsh, and pd-ksh all implement brace expansion this way. | |
561 | ||
d166f048 | 562 | 18) Why doesn't bash have csh variable modifiers? |
ccc6cda3 JA |
563 | |
564 | Posix has specified a more powerful, albeit somewhat more cryptic, | |
565 | mechanism cribbed from ksh, and bash implements it. | |
566 | ||
567 | ${parameter%word} | |
568 | Remove smallest suffix pattern. The WORD is expanded to produce | |
569 | a pattern. It then expands to the value of PARAMETER, with the | |
570 | smallest portion of the suffix matched by the pattern deleted. | |
571 | ||
572 | x=file.c | |
573 | echo ${x%.c}.o | |
574 | -->file.o | |
575 | ||
576 | ${parameter%%word} | |
577 | ||
578 | Remove largest suffix pattern. The WORD is expanded to produce | |
579 | a pattern. It then expands to the value of PARAMETER, with the | |
580 | largest portion of the suffix matched by the pattern deleted. | |
581 | ||
582 | x=posix/src/std | |
583 | echo ${x%%/*} | |
584 | -->posix | |
585 | ||
586 | ${parameter#word} | |
587 | Remove smallest prefix pattern. The WORD is expanded to produce | |
588 | a pattern. It then expands to the value of PARAMETER, with the | |
589 | smallest portion of the prefix matched by the pattern deleted. | |
590 | ||
591 | x=$HOME/src/cmd | |
592 | echo ${x#$HOME} | |
593 | -->/src/cmd | |
594 | ||
595 | ${parameter##word} | |
596 | Remove largest prefix pattern. The WORD is expanded to produce | |
597 | a pattern. It then expands to the value of PARAMETER, with the | |
598 | largest portion of the prefix matched by the pattern deleted. | |
599 | ||
600 | x=/one/two/three | |
601 | echo ${x##*/} | |
602 | -->three | |
603 | ||
604 | ||
605 | Given | |
606 | a=/a/b/c/d | |
607 | b=b.xxx | |
608 | ||
609 | csh bash result | |
610 | --- ---- ------ | |
611 | $a:h ${a%/*} /a/b/c | |
612 | $a:t ${a##*/} d | |
613 | $b:r ${b%.*} b | |
614 | $b:e ${b##*.} xxx | |
615 | ||
616 | ||
d166f048 | 617 | 19) How can I make my csh aliases work when I convert to bash? |
ccc6cda3 JA |
618 | |
619 | Bash uses a different syntax to support aliases than csh does. | |
620 | The details can be found in the documentation. We have provided | |
621 | a shell script which does most of the work of conversion for you; | |
622 | this script can be found in ./examples/misc/alias-conv.sh. Here is | |
623 | how you use it: | |
624 | ||
625 | Start csh in the normal way for you. (e.g., `csh') | |
626 | ||
627 | Pipe the output of `alias' through `alias-conv.sh', saving the | |
628 | results into `bash_aliases': | |
629 | ||
630 | alias | alias-conv.sh >bash_aliases | |
631 | ||
632 | Edit `bash_aliases', carefully reading through any created | |
633 | functions. You will need to change the names of some csh specific | |
634 | variables to the bash equivalents. The script converts $cwd to | |
635 | $PWD, $term to $TERM, $home to $HOME, $user to $USER, and $prompt | |
636 | to $PS1. You may also have to add quotes to avoid unwanted | |
637 | expansion. | |
638 | ||
639 | For example, the csh alias: | |
640 | ||
641 | alias cd 'cd \!*; echo $cwd' | |
642 | ||
643 | is converted to the bash function: | |
644 | ||
645 | cd () { command cd "$@"; echo $PWD ; } | |
646 | ||
647 | The only thing that needs to be done is to quote $PWD: | |
648 | ||
649 | cd () { command cd "$@"; echo "$PWD" ; } | |
650 | ||
651 | Merge the edited file into your ~/.bashrc. | |
652 | ||
653 | There is an additional, more ambitious, script in | |
654 | examples/misc/cshtobash that attempts to convert your entire csh | |
655 | environment to its bash equivalent. This script can be run as | |
656 | simply `cshtobash' to convert your normal interactive | |
657 | environment, or as `cshtobash ~/.login' to convert your login | |
658 | environment. | |
659 | ||
d166f048 | 660 | 20) How can I pipe standard output and standard error from one command to |
ccc6cda3 JA |
661 | another, like csh does with `|&'? |
662 | ||
663 | Use | |
664 | command 2>&1 | command2 | |
665 | ||
666 | The key is to remember that piping is performed before redirection, so | |
667 | file descriptor 1 points to the pipe when it is duplicated onto file | |
668 | descriptor 2. | |
669 | ||
d166f048 | 670 | 21) Now that I've converted from ksh to bash, are there equivalents to |
ccc6cda3 JA |
671 | ksh features like autoloaded functions and the `whence' command? |
672 | ||
673 | There are features in ksh-88 that do not have direct bash equivalents. | |
674 | Most, however, can be emulated with very little trouble. | |
675 | ||
676 | ksh-88 feature Bash equivalent | |
677 | -------------- --------------- | |
678 | [[...]] can usually use [...]; minor differences (no | |
679 | pattern matching, for one) | |
680 | compiled-in aliases set up aliases in .bashrc; some ksh aliases are | |
681 | bash builtins (hash, history, type) | |
682 | $(<file) $(cat file) | |
683 | extended patterns no good substitute | |
684 | coprocesses named pipe pairs (one for read, one for write) | |
685 | typeset +f declare -F | |
686 | cd, print, whence function substitutes in examples/functions/kshenv | |
687 | autoloaded functions examples/functions/autoload is the same as typeset -fu | |
688 | read var?prompt read -p prompt var | |
689 | ||
690 | Section E: How can I get bash to do certain things, and why does bash do | |
691 | things the way it does? | |
692 | ||
d166f048 | 693 | 22) Why is the bash builtin `test' slightly different from /bin/test? |
ccc6cda3 JA |
694 | |
695 | The specific example used here is [ ! x -o x ], which is false. | |
696 | ||
697 | Bash's builtin `test' implements the Posix.2 spec, which can be | |
698 | summarized as follows (the wording is due to David Korn): | |
699 | ||
700 | Here is the set of rules for processing test arguments. | |
701 | ||
702 | 0 Args: False | |
703 | 1 Arg: True iff argument is not null. | |
704 | 2 Args: If first arg is !, True iff second argument is null. | |
705 | If first argument is unary, then true if unary test is true | |
706 | Otherwise error. | |
707 | 3 Args: If second argument is a binary operator, do binary test of $1 $3 | |
708 | If first argument is !, negate two argument test of $2 $3 | |
709 | If first argument is `(' and third argument is `)', do the | |
710 | one-argument test of the second argument. | |
711 | Otherwise error. | |
712 | 4 Args: If first argument is !, negate three argument test of $2 $3 $4. | |
713 | Otherwise unspecified | |
714 | 5 or more Args: unspecified. (Historical shells would use their | |
715 | current algorithm). | |
716 | ||
717 | The operators -a and -o are considered binary operators for the purpose | |
718 | of the 3 Arg case. | |
719 | ||
720 | As you can see, the test becomes (not (x or x)), which is false. | |
721 | ||
d166f048 | 722 | 23) Why does bash sometimes say `Broken pipe'? |
ccc6cda3 JA |
723 | |
724 | If a sequence of commands appears in a pipeline, and one of the | |
725 | reading commands finishes before the writer has finished, the | |
726 | writer receives a SIGPIPE signal. Many other shells special-case | |
727 | SIGPIPE as an exit status in the pipeline and do not report it. | |
728 | For example, in: | |
729 | ||
730 | ps -aux | head | |
731 | ||
732 | `head' can finish before `ps' writes all of its output, and ps | |
733 | will try to write on a pipe without a reader. In that case, bash | |
734 | will print `Broken pipe' to stderr when ps is killed by a | |
735 | SIGPIPE. | |
736 | ||
d166f048 | 737 | 24) How can I get bash to read and display eight-bit characters? |
ccc6cda3 JA |
738 | |
739 | This is a process requiring several steps. | |
740 | ||
741 | First, you must ensure that the `physical' data path is a full eight | |
742 | bits. For xterms, for example, the `vt100' resources `eightBitInput' | |
743 | and `eightBitOutput' should be set to `true'. | |
744 | ||
745 | Once you have set up an eight-bit path, you must tell the kernel and | |
746 | tty driver to leave the eighth bit of characters alone when processing | |
747 | keyboard input. Use `stty' to do this: | |
748 | ||
749 | stty cs8 -istrip -parenb | |
750 | ||
751 | For old BSD-style systems, you can use | |
752 | ||
753 | stty pass8 | |
754 | ||
755 | You may also need | |
756 | ||
757 | stty even odd | |
758 | ||
759 | Finally, you need to tell readline that you will be inputting and | |
760 | displaying eight-bit characters. You use readline variables to do | |
761 | this. These variables can be set in your .inputrc or using the bash | |
762 | `bind' builtin. Here's an example using `bind': | |
763 | ||
764 | bash$ bind 'set convert-meta off' | |
765 | bash$ bind 'set meta-flag on' | |
766 | bash$ bind 'set output-meta on' | |
767 | ||
768 | The `set' commands between the single quotes may also be placed | |
769 | in ~/.inputrc. | |
770 | ||
d166f048 | 771 | 25) How do I write a function `x' to replace builtin command `x', but |
ccc6cda3 JA |
772 | still invoke the command from within the function? |
773 | ||
774 | This is why the `command' and `builtin' builtins exist. The | |
775 | `command' builtin executes the command supplied as its first | |
776 | argument, skipping over any function defined with that name. The | |
777 | `builtin' builtin executes the builtin command given as its first | |
778 | argument directly. | |
779 | ||
780 | For example, to write a function to replace `cd' that writes the | |
781 | hostname and current directory to an xterm title bar, use | |
782 | something like the following: | |
783 | ||
784 | cd() | |
785 | { | |
786 | builtin cd "$@" && xtitle "$HOST: $PWD" | |
787 | } | |
788 | ||
789 | This could also be written using `command' instead of `builtin'; | |
790 | the version above is marginally more efficient. | |
791 | ||
d166f048 | 792 | 26) When I have terminal escape sequences in my prompt, why does bash |
ccc6cda3 JA |
793 | wrap lines at the wrong column? |
794 | ||
795 | Readline, the line editing library that bash uses, does not know | |
796 | that the terminal escape sequences do not take up space on the | |
797 | screen. The redisplay code assumes, unless told otherwise, that | |
798 | each character in the prompt is a `printable' character that | |
799 | takes up one character position on the screen. | |
800 | ||
801 | You can use the bash prompt expansion facility (see the PROMPTING | |
802 | section in the manual page) to tell readline that sequences of | |
803 | characters in the prompt strings take up no screen space. | |
804 | ||
805 | Use the \[ escape to begin a sequence of non-printing characters, | |
806 | and the \] escape to signal the end of such a sequence. | |
807 | ||
d166f048 | 808 | 27) How can I find the value of a shell variable whose name is the value |
ccc6cda3 JA |
809 | of another shell variable? |
810 | ||
d166f048 | 811 | Bash-2.01 supports this directly. You can use |
ccc6cda3 JA |
812 | |
813 | ${!var} | |
814 | ||
815 | For example, the following sequence of commands will echo `z': | |
816 | ||
817 | var1=var2 | |
818 | var2=z | |
819 | echo ${!var1} | |
820 | ||
821 | For sh compatibility, use the `eval' builtin. The important | |
822 | thing to remember is that `eval' expands the arguments you give | |
823 | it again, so you need to quote the parts of the arguments that | |
824 | you want `eval' to act on. | |
825 | ||
826 | For example, this expression prints the value of the last positional | |
827 | parameter: | |
828 | ||
829 | eval echo \"\$\{$#\}\" | |
830 | ||
831 | The expansion of the quoted portions of this expression will be | |
832 | deferred until `eval' runs, while the `$#' will be expanded | |
d166f048 | 833 | before `eval' is executed. In bash-2.01, |
ccc6cda3 JA |
834 | |
835 | echo ${!#} | |
836 | ||
837 | does the same thing. | |
838 | ||
d166f048 | 839 | 28) If I pipe the output of a command into `read variable', why doesn't |
ccc6cda3 JA |
840 | the output show up in $variable when the read command finishes? |
841 | ||
842 | This has to do with the parent-child relationship between Unix | |
843 | processes. | |
844 | ||
845 | Each element of a pipeline runs in a separate process, a child of | |
846 | the shell running the pipeline. A subprocess cannot affect its | |
847 | parent's environment. When the `read' command sets the variable | |
848 | to the input, that variable is set only in the subshell, not the | |
849 | parent shell. When the subshell exits, the value of the variable | |
850 | is lost. | |
851 | ||
852 | Many pipelines that end with `read variable' can be converted | |
853 | into command substitutions, which will capture the output of | |
854 | a specified command. The output can then be assigned to a | |
855 | variable: | |
856 | ||
857 | grep ^gnu /usr/lib/news/active | wc -l | read ngroup | |
858 | ||
859 | can be converted into | |
860 | ||
861 | ngroup=$(grep ^gnu /usr/lib/news/active | wc -l) | |
862 | ||
863 | This does not, unfortunately, work to split the text among | |
864 | multiple variables, as read does when given multiple variable | |
865 | arguments. If you need to do this, you can either use the | |
866 | command substitution above to read the output into a variable | |
867 | and chop up the variable using the bash pattern removal | |
868 | expansion operators or use some variant of the following | |
869 | approach. | |
870 | ||
871 | Say /usr/local/bin/ipaddr is the following shell script: | |
872 | ||
873 | #! /bin/sh | |
874 | host `hostname` | awk '/address/ {print $NF}' | |
875 | ||
876 | Instead of using | |
877 | ||
878 | /usr/local/bin/ipaddr | read A B C D | |
879 | ||
880 | to break the local machine's IP address into separate octets, use | |
881 | ||
882 | OIFS="$IFS" | |
883 | IFS=. | |
884 | set -- $(/usr/local/bin/ipaddr) | |
885 | IFS="$OIFS" | |
886 | A="$1" B="$2" C="$3" D="$4" | |
887 | ||
888 | Beware, however, that this will change the shell's positional | |
889 | parameters. If you need them, you should save them before doing | |
890 | this. | |
891 | ||
892 | This is the general approach -- in most cases you will not need to | |
893 | set $IFS to a different value. | |
894 | ||
d166f048 | 895 | 29) I have a bunch of shell scripts that use backslash-escaped characters |
ccc6cda3 JA |
896 | in arguments to `echo'. Bash doesn't interpret these characters. Why |
897 | not, and how can I make it understand them? | |
898 | ||
899 | This is the behavior of echo on most Unix System V machines. | |
900 | ||
901 | The bash builtin `echo' is modelled after the 9th Edition | |
902 | Research Unix version of `echo'. It does not interpret | |
903 | backslash-escaped characters in its argument strings by default; | |
904 | it requires the use of the -e option to enable the | |
905 | interpretation. The System V echo provides no way to disable the | |
906 | special characters; the bash echo has a -E option to disable | |
907 | them. | |
908 | ||
909 | There is a configuration option that will make bash behave like | |
910 | the System V echo and interpret things like `\t' by default. Run | |
911 | configure with the --enable-usg-echo-default option to turn this | |
912 | on. Be aware that this will cause some of the tests run when you | |
913 | type `make tests' to fail. | |
914 | ||
d166f048 | 915 | 30) Why doesn't a while or for loop get suspended when I type ^Z? |
ccc6cda3 JA |
916 | |
917 | This is a consequence of how job control works on Unix. The only | |
918 | thing that can be suspended is the process group. This is a single | |
919 | command or pipeline of commands that the shell forks and executes. | |
920 | ||
921 | When you run a while or for loop, the only thing that the shell forks | |
922 | and executes are any commands in the while loop test and commands in | |
923 | the loop bodies. These, therefore, are the only things that can be | |
924 | suspended when you type ^Z. | |
925 | ||
926 | If you want to be able to stop the entire loop, you need to put it | |
927 | within parentheses, which will force the loop into a subshell that | |
928 | may be stopped (and subsequently restarted) as a single unit. | |
929 | ||
d166f048 | 930 | 31) How can I make the bash `time' reserved word print timing output that |
ccc6cda3 JA |
931 | looks like the output from my system's /usr/bin/time? |
932 | ||
933 | The bash command timing code looks for a variable `TIMEFORMAT' and | |
934 | uses its value as a format string to decide how to display the | |
935 | timing statistics. | |
936 | ||
937 | The value of TIMEFORMAT is a string with `%' escapes expanded in a | |
938 | fashion similar in spirit to printf(3). The manual page explains | |
939 | the meanings of the escape sequences in the format string. | |
940 | ||
941 | If TIMEFORMAT is not set, bash acts as if the following assignment had | |
942 | been performed: | |
943 | ||
944 | TIMEFORMAT=$'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS' | |
945 | ||
946 | The POSIX.2 default time format (used by `time -p command') is | |
947 | ||
948 | TIMEFORMAT=$'real %2R\nuser %2U\nsys %2S' | |
949 | ||
950 | The BSD /usr/bin/time format can be emulated with: | |
951 | ||
952 | TIMEFORMAT=$'\t%1R real\t%1U user\t%1S sys' | |
953 | ||
954 | The System V /usr/bin/time format can be emulated with: | |
955 | ||
956 | TIMEFORMAT=$'\nreal\t%1R\nuser\t%1U\nsys\t%1S' | |
957 | ||
958 | The ksh format can be emulated with: | |
959 | ||
960 | TIMEFORMAT=$'\nreal\t%2lR\nuser\t%2lU\nsys\t%2lS' | |
961 | ||
962 | Section F: Things to watch out for on certain Unix versions | |
963 | ||
d166f048 | 964 | 32) Why can't I use command line editing in my `cmdtool'? |
ccc6cda3 JA |
965 | |
966 | The problem is `cmdtool' and bash fighting over the input. When | |
967 | scrolling is enabled in a cmdtool window, cmdtool puts the tty in | |
968 | `raw mode' to permit command-line editing using the mouse for | |
969 | applications that cannot do it themselves. As a result, bash and | |
970 | cmdtool each try to read keyboard input immediately, with neither | |
971 | getting enough of it to be useful. | |
972 | ||
973 | This mode also causes cmdtool to not implement many of the | |
974 | terminal functions and control sequences appearing in the | |
975 | `sun-cmd' termcap entry. For a more complete explanation, see | |
976 | that file examples/suncmd.termcap in the bash distribution. | |
977 | ||
978 | `xterm' is a better choice, and gets along with bash much more | |
979 | smoothly. | |
980 | ||
981 | If you must use cmdtool, you can use the termcap description in | |
982 | examples/suncmd.termcap. Set the TERMCAP variable to the terminal | |
983 | description contained in that file, i.e. | |
984 | ||
985 | TERMCAP='Mu|sun-cmd:am:bs:km:pt:li#34:co#80:cl=^L:ce=\E[K:cd=\E[J:rs=\E[s:' | |
986 | ||
987 | Then export TERMCAP and start a new cmdtool window from that shell. | |
988 | The bash command-line editing should behave better in the new | |
989 | cmdtool. If this works, you can put the assignment to TERMCAP | |
990 | in your bashrc file. | |
991 | ||
d166f048 | 992 | 33) I built bash on Solaris 2. Why do globbing expansions and filename |
ccc6cda3 JA |
993 | completion chop off the first few characters of each filename? |
994 | ||
995 | This is the consequence of building bash on SunOS 5 and linking | |
996 | with the libraries in /usr/ucblib, but using the definitions | |
997 | and structures from files in /usr/include. | |
998 | ||
999 | The actual conflict is between the dirent structure in | |
1000 | /usr/include/dirent.h and the struct returned by the version of | |
1001 | `readdir' in libucb.a (a 4.3-BSD style `struct direct'). | |
1002 | ||
1003 | Make sure you've got /usr/ccs/bin ahead of /usr/ucb in your $PATH | |
1004 | when configuring and building bash. This will ensure that you | |
1005 | use /usr/ccs/bin/cc or acc instead of /usr/ucb/cc and that you | |
1006 | link with libc before libucb. | |
1007 | ||
1008 | If you have installed the Sun C compiler, you may also need to | |
1009 | put /usr/ccs/bin and /opt/SUNWspro/bin into your $PATH before | |
1010 | /usr/ucb. | |
1011 | ||
d166f048 | 1012 | 34) Why does bash dump core after I interrupt username completion or |
ccc6cda3 JA |
1013 | `~user' tilde expansion on a machine running NIS? |
1014 | ||
1015 | This is a famous and long-standing bug in the SunOS YP (sorry, NIS) | |
1016 | client library, which is part of libc. | |
1017 | ||
1018 | The YP library code keeps static state -- a pointer into the data | |
1019 | returned from the server. When YP initializes itself (setpwent), | |
1020 | it looks at this pointer and calls free on it if it's non-null. | |
1021 | So far, so good. | |
1022 | ||
1023 | If one of the YP functions is interrupted during getpwent (the | |
1024 | exact function is interpretwithsave()), and returns NULL, the | |
1025 | pointer is freed without being reset to NULL, and the function | |
1026 | returns. The next time getpwent is called, it sees that this | |
1027 | pointer is non-null, calls free, and the bash free() blows up | |
1028 | because it's being asked to free freed memory. | |
1029 | ||
1030 | The traditional Unix mallocs allow memory to be freed multiple | |
1031 | times; that's probably why this has never been fixed. You can | |
1032 | run configure with the `--without-gnu-malloc' option to use | |
1033 | the C library malloc and avoid the problem. | |
1034 | ||
d166f048 | 1035 | 35) I'm running SVR4.2. Why is the line erased every time I type `@'? |
ccc6cda3 JA |
1036 | |
1037 | The `@' character is the default `line kill' character in most | |
1038 | versions of System V, including SVR4.2. You can change this | |
1039 | character to whatever you want using `stty'. For example, to | |
1040 | change the line kill character to control-u, type | |
1041 | ||
1042 | stty kill ^U | |
1043 | ||
1044 | where the `^' and `U' can be two separate characters. | |
1045 | ||
d166f048 | 1046 | 36) Why does bash report syntax errors when my C News scripts use a |
ccc6cda3 JA |
1047 | redirection before a subshell command? |
1048 | ||
1049 | The actual command in question is something like | |
1050 | ||
1051 | < file ( command ) | |
1052 | ||
1053 | According to the grammar given in the POSIX.2 standard, this construct | |
1054 | is, in fact, a syntax error. Redirections may only precede `simple | |
1055 | commands'. A subshell construct such as the above is one of the shell's | |
1056 | `compound commands'. A redirection may only follow a compound command. | |
1057 | ||
d166f048 | 1058 | The file CWRU/sh-redir-hack in the bash-2.01 distribution is an |
ccc6cda3 JA |
1059 | (unofficial) patch to parse.y that will modify the grammar to |
1060 | support this construct. It will not apply with `patch'; you must | |
1061 | modify parse.y by hand. Note that if you apply this, you must | |
1062 | recompile with -DREDIRECTION_HACK. This introduces a large | |
1063 | number of reduce/reduce conflicts into the shell grammar. | |
1064 | ||
1065 | Section G: Where do I go from here? | |
1066 | ||
d166f048 | 1067 | 37) How do I report bugs in bash, and where should I look for fixes and |
ccc6cda3 JA |
1068 | advice? |
1069 | ||
1070 | Use the `bashbug' script to report bugs. It is built and | |
1071 | installed at the same time as bash. It provides a standard | |
1072 | template for reporting a problem and automatically includes | |
1073 | information about your configuration and build environment. | |
1074 | ||
1075 | `bashbug' sends its reports to bug-bash@prep.ai.mit.edu, which | |
1076 | is a large mailing list gatewayed to the usenet newsgroup gnu.bash.bug. | |
1077 | ||
1078 | Bug fixes, answers to questions, and announcements of new releases | |
1079 | are all posted to gnu.bash.bug. Discussions concerning bash features | |
1080 | and problems also take place there. | |
1081 | ||
1082 | To reach the bash maintainers directly, send mail to | |
1083 | bash-maintainers@prep.ai.mit.edu. | |
1084 | ||
d166f048 | 1085 | 38) What kind of bash documentation is there? |
ccc6cda3 JA |
1086 | |
1087 | First, look in the doc directory in the bash distribution. It should | |
1088 | contain at least the following files: | |
1089 | ||
1090 | bash.1 an extensive, thorough Unix-style manual page | |
1091 | builtins.1 a manual page covering just bash builtin commands | |
1092 | bashref.texi a reference manual in GNU info format | |
1093 | bash.html an HTML version of the manual page | |
1094 | bashref.html an HTML version of the reference manual | |
1095 | FAQ this file | |
1096 | article.ms text of an article written for The Linux Journal | |
1097 | readline.3 a man page describing readline | |
1098 | ||
1099 | Postscript files created from the above source are available in | |
1100 | the documentation distribution. | |
1101 | ||
1102 | There is additional documentation available for anonymous FTP from host | |
1103 | slc2.ins.cwru.edu in the `pub/bash' directory. | |
1104 | ||
1105 | Cameron Newham and Bill Rosenblatt have written a book on bash, published | |
1106 | by O'Reilly and Associates. The book is based on Bill Rosenblatt's Korn | |
d166f048 JA |
1107 | Shell book. The title is ``Learning the Bash Shell'', and the ISBN number |
1108 | is 1-56592-147-X. Look for it in fine bookstores near you. This book | |
1109 | covers bash-1.14, but has an appendix describing some of the new features | |
1110 | in bash-2.0. There are rumors of a second edition of this book, describing | |
1111 | bash-2.0 (and 2.01). I do not know what ORA's publication schedule for | |
1112 | this edition is. | |
ccc6cda3 | 1113 | |
d166f048 | 1114 | 39) What's coming in future versions? |
ccc6cda3 JA |
1115 | |
1116 | These are features I plan to include in a future version of bash. | |
1117 | ||
1118 | POSIX.2-style globbing character classes ([:alpha:], [:alnum:], etc.) | |
d166f048 JA |
1119 | POSIX.2-style globbing equivalence classes |
1120 | POSIX.2-style globbing collating symbols | |
1121 | a bash debugger (a minimally-tested version is included with bash-2.01) | |
ccc6cda3 | 1122 | |
d166f048 | 1123 | 40) What's on the bash `wish list' for future versions? |
ccc6cda3 JA |
1124 | |
1125 | These are features that may or may not appear in a future version of bash. | |
1126 | ||
1127 | Programmable completion a la zsh | |
1128 | menu completion a la tcsh | |
1129 | the ksh [[...]] extended test command | |
1130 | the ksh egrep-style extended pattern matching operators | |
1131 | associative arrays (not really all that hard) | |
1132 | breaking some of the shell functionality into embeddable libraries | |
1133 | better internationalization using GNU `gettext' | |
1134 | an option to use external files for the long `help' text | |
1135 | timeouts for the `read' builtin | |
1136 | the ksh-93 ${!prefix*} and ${!prefix@} operators | |
1137 | arithmetic ++ and -- prefix and postfix operators | |
1138 | ||
d166f048 | 1139 | 41) When will the next release appear? |
ccc6cda3 JA |
1140 | |
1141 | The next version will appear sometime in 1997. Never make predictions. | |
1142 | ||
1143 | ||
1144 | This document is Copyright 1995, 1996 by Chester Ramey. | |
1145 | ||
1146 | Permission is hereby granted, without written agreement and | |
1147 | without license or royalty fees, to use, copy, and distribute | |
1148 | this document for any purpose, provided that the above copyright | |
1149 | notice appears in all copies of this document and that the | |
1150 | contents of this document remain unaltered. |