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28ef6c31 | 1 | This is the Bash FAQ, version 3.11, for Bash version 2.05. |
ccc6cda3 JA |
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 | ||
cce855bc | 16 | ftp://ftp.cwru.edu/pub/bash/FAQ |
ccc6cda3 | 17 | |
bb70624e JA |
18 | The Bash home page is http://cnswww.cns.cwru.edu/~chet/bash/bashtop.html |
19 | ||
ccc6cda3 JA |
20 | ---------- |
21 | Contents: | |
22 | ||
23 | Section A: The Basics | |
24 | ||
b72432fd JA |
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'? | |
ccc6cda3 JA |
36 | |
37 | Section B: The latest version | |
38 | ||
28ef6c31 JA |
39 | B1) What's new in version 2.05? |
40 | B2) Are there any user-visible incompatibilities between bash-2.05 and | |
ccc6cda3 JA |
41 | bash-1.14.7? |
42 | ||
43 | Section C: Differences from other Unix shells | |
44 | ||
b72432fd JA |
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? | |
ccc6cda3 JA |
48 | |
49 | Section D: Why does bash do some things differently than other Unix shells? | |
50 | ||
b72432fd | 51 | D1) Why does bash run a different version of `command' than |
ccc6cda3 | 52 | `which command' says it will? |
b72432fd JA |
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 | |
ccc6cda3 | 57 | another, like csh does with `|&'? |
b72432fd | 58 | D6) Now that I've converted from ksh to bash, are there equivalents to |
ccc6cda3 JA |
59 | ksh features like autoloaded functions and the `whence' command? |
60 | ||
bb70624e | 61 | Section E: Why does bash do certain things the way it does? |
ccc6cda3 | 62 | |
b72432fd JA |
63 | E1) Why is the bash builtin `test' slightly different from /bin/test? |
64 | E2) Why does bash sometimes say `Broken pipe'? | |
bb70624e | 65 | E3) When I have terminal escape sequences in my prompt, why does bash |
ccc6cda3 | 66 | wrap lines at the wrong column? |
bb70624e | 67 | E4) If I pipe the output of a command into `read variable', why doesn't |
ccc6cda3 | 68 | the output show up in $variable when the read command finishes? |
bb70624e | 69 | E5) I have a bunch of shell scripts that use backslash-escaped characters |
ccc6cda3 JA |
70 | in arguments to `echo'. Bash doesn't interpret these characters. Why |
71 | not, and how can I make it understand them? | |
bb70624e | 72 | E6) Why doesn't a while or for loop get suspended when I type ^Z? |
28ef6c31 JA |
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'? | |
ccc6cda3 JA |
77 | |
78 | Section F: Things to watch out for on certain Unix versions | |
79 | ||
b72432fd JA |
80 | F1) Why can't I use command line editing in my `cmdtool'? |
81 | F2) I built bash on Solaris 2. Why do globbing expansions and filename | |
ccc6cda3 | 82 | completion chop off the first few characters of each filename? |
b72432fd | 83 | F3) Why does bash dump core after I interrupt username completion or |
ccc6cda3 | 84 | `~user' tilde expansion on a machine running NIS? |
b72432fd JA |
85 | F4) I'm running SVR4.2. Why is the line erased every time I type `@'? |
86 | F5) Why does bash report syntax errors when my C News scripts use a | |
ccc6cda3 | 87 | redirection before a subshell command? |
bb70624e JA |
88 | F6) Why can't I use vi-mode editing on Red Hat Linux 6.1? |
89 | ||
90 | Section G: How can I get bash to do certain common things? | |
91 | ||
92 | G1) How can I get bash to read and display eight-bit characters? | |
93 | G2) How do I write a function `x' to replace builtin command `x', but | |
94 | still invoke the command from within the function? | |
95 | G3) How can I find the value of a shell variable whose name is the value | |
96 | of another shell variable? | |
97 | G4) How can I make the bash `time' reserved word print timing output that | |
98 | looks like the output from my system's /usr/bin/time? | |
99 | G5) How do I get the current directory into my prompt? | |
100 | G6) How can I rename "*.foo" to "*.bar"? | |
101 | G7) How can I translate a filename from uppercase to lowercase? | |
102 | G8) How can I write a filename expansion (globbing) pattern that will match | |
103 | all files in the current directory except "." and ".."? | |
ccc6cda3 | 104 | |
bb70624e | 105 | Section H: Where do I go from here? |
ccc6cda3 | 106 | |
bb70624e | 107 | H1) How do I report bugs in bash, and where should I look for fixes and |
ccc6cda3 | 108 | advice? |
bb70624e JA |
109 | H2) What kind of bash documentation is there? |
110 | H3) What's coming in future versions? | |
111 | H4) What's on the bash `wish list'? | |
112 | H5) When will the next release appear? | |
ccc6cda3 JA |
113 | |
114 | ---------- | |
115 | Section A: The Basics | |
116 | ||
b72432fd | 117 | A1) What is it? |
ccc6cda3 JA |
118 | |
119 | Bash is a Unix command interpreter (shell). It is an implementation of | |
120 | the Posix 1003.2 shell standard, and resembles the Korn and System V | |
121 | shells. | |
122 | ||
123 | Bash contains a number of enhancements over those shells, both | |
124 | for interactive use and shell programming. Features geared | |
125 | toward interactive use include command line editing, command | |
126 | history, job control, aliases, and prompt expansion. Programming | |
127 | features include additional variable expansions, shell | |
128 | arithmetic, and a number of variables and options to control | |
129 | shell behavior. | |
130 | ||
131 | Bash was originally written by Brian Fox of the Free Software | |
132 | Foundation. The current developer and maintainer is Chet Ramey | |
133 | of Case Western Reserve University. | |
134 | ||
b72432fd | 135 | A2) What's the latest version? |
ccc6cda3 | 136 | |
28ef6c31 | 137 | The latest version is 2.05, first made available on Monday, 9 April 2001. |
ccc6cda3 | 138 | |
b72432fd | 139 | A3) Where can I get it? |
ccc6cda3 JA |
140 | |
141 | Bash is the GNU project's shell, and so is available from the | |
b72432fd | 142 | master GNU archive site, ftp.gnu.org, and its mirrors. The |
cce855bc | 143 | latest version is also available for FTP from ftp.cwru.edu. |
28ef6c31 | 144 | The following URLs tell how to get version 2.05: |
ccc6cda3 | 145 | |
28ef6c31 JA |
146 | ftp://ftp.gnu.org/pub/gnu/bash/bash-2.05.tar.gz |
147 | ftp://ftp.cwru.edu/pub/bash/bash-2.05.tar.gz | |
ccc6cda3 JA |
148 | |
149 | Formatted versions of the documentation are available with the URLs: | |
150 | ||
28ef6c31 JA |
151 | ftp://ftp.gnu.org/pub/gnu/bash/bash-doc-2.05.tar.gz |
152 | ftp://ftp.cwru.edu/pub/bash/bash-doc-2.05.tar.gz | |
ccc6cda3 | 153 | |
b72432fd | 154 | A4) On what machines will bash run? |
ccc6cda3 JA |
155 | |
156 | Bash has been ported to nearly every version of UNIX. All you | |
157 | should have to do to build it on a machine for which a port | |
158 | exists is to type `configure' and then `make'. The build process | |
159 | will attempt to discover the version of UNIX you have and tailor | |
160 | itself accordingly, using a script created by GNU autoconf. | |
161 | ||
162 | More information appears in the file `INSTALL' in the distribution. | |
163 | ||
b72432fd | 164 | A5) Will bash run on operating systems other than Unix? |
d166f048 JA |
165 | |
166 | Configuration specifics for Unix-like systems such as QNX and | |
28ef6c31 | 167 | LynxOS are included in the distribution. Bash-2.05 should |
bc4cd23c JA |
168 | compile and run on Minix 2.0 (patches were contributed), but I |
169 | don't believe anyone has built bash-2.x on earlier Minix versions | |
170 | yet. | |
d166f048 JA |
171 | |
172 | Bash has been ported to versions of Windows implementing the Win32 | |
173 | programming interface. This includes Windows 95 and Windows NT. | |
bb70624e | 174 | The port was done by Cygnus Solutions as part of their CYGWIN |
28ef6c31 | 175 | project. For more information about the project, look at the URLs |
d166f048 | 176 | |
28ef6c31 JA |
177 | http://www.cygwin.com/ |
178 | http://sourceware.cygnus.com/cygwin | |
d166f048 | 179 | |
b72432fd | 180 | Cygnus originally ported bash-1.14.7, and that port was part of their |
bb70624e | 181 | early GNU-Win32 (the original name) releases. Cygnus has also done a |
28ef6c31 JA |
182 | port of bash-2.04 to the CYGWIN environment, and it is available as |
183 | part of their current release. | |
cce855bc | 184 | |
28ef6c31 | 185 | Bash-2.05 should require no local Cygnus changes to build and run under |
bb70624e | 186 | CYGWIN. |
cce855bc JA |
187 | |
188 | The Cygnus port works only on Intel machines. There is a port of bash | |
189 | (I don't know which version) to the alpha/NT environment available from | |
190 | ||
191 | ftp://ftp.gnustep.org//pub/win32/bash-alpha-nt-1.01.tar.gz | |
192 | ||
28ef6c31 JA |
193 | DJ Delorie has a port of bash-1.14.7 which runs under MS-DOS, as part |
194 | of the DJGPP project. For more information on the project, see | |
d166f048 JA |
195 | |
196 | http://www.delorie.com/djgpp/ | |
197 | ||
28ef6c31 JA |
198 | I have been told that the original DJGPP port was done by Daisuke Aoyama. |
199 | ||
d166f048 JA |
200 | I picked up a binary of bash-1.14.7 that is purported to work with |
201 | the DJGPP V2 environment from | |
202 | ||
203 | ftp://ftp.simtel.net/pub/simtelnet/gnu/djgpp/v2gnu/bsh1147b.zip | |
204 | ||
205 | The corresponding source is | |
206 | ||
207 | ftp://ftp.simtel.net/pub/simtelnet/gnu/djgpp/v2gnu/bsh1147s.zip | |
208 | ||
bb70624e JA |
209 | Mark Elbrecht <snowball3@bigfoot.com> has sent me notice that bash-2.03 |
210 | has become available for DJGPP V2. The files are available as: | |
211 | ||
212 | ftp://ftp.simtel.net/pub/simtelnet/gnu/djgpp/v2gnu/bsh203b.zip binary | |
213 | ftp://ftp.simtel.net/pub/simtelnet/gnu/djgpp/v2gnu/bsh203d.zip documentation | |
214 | ftp://ftp.simtel.net/pub/simtelnet/gnu/djgpp/v2gnu/bsh203s.zip source | |
215 | ||
216 | Mark has begun to work with bash-2.04. | |
217 | ||
cce855bc | 218 | Ports of bash-1.12 and bash-2.0 are available for OS/2 from |
d166f048 | 219 | |
cce855bc JA |
220 | ftp://hobbes.nmsu.edu/pub/os2/util/shell/bash_112.zip |
221 | ftp://hobbes.nmsu.edu/pub/os2/util/shell/bash-2.0(253).zip | |
d166f048 | 222 | |
cce855bc JA |
223 | I haven't looked at either, but the second appears to be a binary-only |
224 | distribution. Beware. | |
d166f048 | 225 | |
bb70624e JA |
226 | I have received word that Bash (I'm not sure which version, but I |
227 | believe that it's at least bash-2.02.1) is the standard shell on | |
228 | BeOS. | |
229 | ||
b72432fd | 230 | A6) How can I build bash with gcc? |
ccc6cda3 JA |
231 | |
232 | Bash configures to use gcc by default if it is available. Read the | |
233 | file INSTALL in the distribution for more information. | |
234 | ||
b72432fd | 235 | A7) How can I make bash my login shell? |
ccc6cda3 JA |
236 | |
237 | Some machines let you use `chsh' to change your login shell. Other | |
cce855bc JA |
238 | systems use `passwd -s' or `passwd -e'. If one of these works for |
239 | you, that's all you need. Note that many systems require the full | |
240 | pathname to a shell to appear in /etc/shells before you can make it | |
241 | your login shell. For this, you may need the assistance of your | |
242 | friendly local system administrator. | |
ccc6cda3 JA |
243 | |
244 | If you cannot do this, you can still use bash as your login shell, but | |
245 | you need to perform some tricks. The basic idea is to add a command | |
246 | to your login shell's startup file to replace your login shell with | |
247 | bash. | |
248 | ||
249 | For example, if your login shell is csh or tcsh, and you have installed | |
250 | bash in /usr/gnu/bin/bash, add the following line to ~/.login: | |
251 | ||
252 | if ( -f /usr/gnu/bin/bash ) exec /usr/gnu/bin/bash --login | |
253 | ||
254 | (the `--login' tells bash that it is a login shell). | |
255 | ||
256 | It's not a good idea to put this command into ~/.cshrc, because every | |
257 | csh you run without the `-f' option, even ones started to run csh scripts, | |
258 | reads that file. If you must put the command in ~/.cshrc, use something | |
259 | like | |
260 | ||
261 | if ( $?prompt ) exec /usr/gnu/bin/bash --login | |
262 | ||
263 | to ensure that bash is exec'd only when the csh is interactive. | |
264 | ||
d166f048 | 265 | If your login shell is sh or ksh, you have to do two things. |
ccc6cda3 | 266 | |
d166f048 | 267 | First, create an empty file in your home directory named `.bash_profile'. |
ccc6cda3 JA |
268 | The existence of this file will prevent the exec'd bash from trying to |
269 | read ~/.profile, and re-execing itself over and over again. ~/.bash_profile | |
d166f048 JA |
270 | is the first file bash tries to read initialization commands from when |
271 | it is invoked as a login shell. | |
272 | ||
273 | Next, add a line similar to the above to ~/.profile: | |
274 | ||
275 | [ -f /usr/gnu/bin/bash ] && exec /usr/gnu/bin/bash --login | |
ccc6cda3 | 276 | |
d166f048 JA |
277 | This will cause login shells to replace themselves with bash running as |
278 | a login shell. Once you have this working, you can copy your initialization | |
279 | code from ~/.profile to ~/.bash_profile. | |
280 | ||
bb70624e JA |
281 | I have received word that the recipe supplied above is insufficient for |
282 | machines running CDE. CDE has a maze of twisty little startup files, all | |
283 | slightly different. | |
284 | ||
285 | If you cannot change your login shell in the password file to bash, you | |
286 | will have to (apparently) live with CDE using the shell in the password | |
287 | file to run its startup scripts. If you have changed your shell to bash, | |
288 | there is code in the CDE startup files (on Solaris, at least) to do the | |
289 | right thing. | |
290 | ||
291 | `dtterm' claims to use $SHELL as the default program to start, so if you | |
292 | can change $SHELL in the CDE startup files, you should be able to use bash | |
293 | in your terminal windows. | |
294 | ||
295 | Setting DTSOURCEPROFILE in ~/.dtprofile will cause the `Xsession' program | |
296 | to read your login shell's startup files. You may be able to use bash for | |
297 | the rest of the CDE programs by setting SHELL to bash in ~/.dtprofile as | |
298 | well, but I have not tried this. | |
299 | ||
300 | You can use the above `exec' recipe to start bash when not logging in with | |
301 | CDE by testing the value of the DT variable: | |
302 | ||
303 | if [ -n "$DT" ]; then | |
304 | [ -f /usr/gnu/bin/bash ] && exec /usr/gnu/bin/bash --login | |
305 | fi | |
306 | ||
307 | ||
b72432fd | 308 | A8) I just changed my login shell to bash, and now I can't FTP into my |
ccc6cda3 JA |
309 | machine. Why not? |
310 | ||
311 | You must add the full pathname to bash to the file /etc/shells. As | |
312 | noted in the answer to the previous question, many systems require | |
313 | this before you can make bash your login shell. | |
314 | ||
315 | Most versions of ftpd use this file to prohibit `special' users | |
316 | such as `uucp' and `news' from using FTP. | |
317 | ||
b72432fd | 318 | A9) What's the `POSIX 1003.2 standard'? |
ccc6cda3 JA |
319 | |
320 | POSIX is a name originally coined by Richard Stallman for a | |
321 | family of open system standards based on UNIX. There are a | |
322 | number of aspects of UNIX under consideration for | |
323 | standardization, from the basic system services at the system | |
324 | call and C library level to applications and tools to system | |
325 | administration and management. Each area of standardization is | |
326 | assigned to a working group in the 1003 series. | |
327 | ||
328 | The POSIX Shell and Utilities standard has been developed by IEEE | |
329 | Working Group 1003.2 (POSIX.2). It concentrates on the command | |
330 | interpreter interface and utility programs commonly executed from | |
331 | the command line or by other programs. An initial version of the | |
332 | standard has been approved and published by the IEEE, and work is | |
333 | currently underway to update it. | |
334 | ||
335 | Bash is concerned with the aspects of the shell's behavior | |
336 | defined by POSIX.2. The shell command language has of course | |
337 | been standardized, including the basic flow control and program | |
338 | execution constructs, I/O redirection and pipelining, argument | |
339 | handling, variable expansion, and quoting. | |
340 | ||
341 | The `special' builtins, which must be implemented as part of the | |
342 | shell to provide the desired functionality, are specified as | |
343 | being part of the shell; examples of these are `eval' and | |
344 | `export'. Other utilities appear in the sections of POSIX.2 not | |
345 | devoted to the shell which are commonly (and in some cases must | |
346 | be) implemented as builtin commands, such as `read' and `test'. | |
347 | POSIX.2 also specifies aspects of the shell's interactive | |
348 | behavior as part of the UPE, including job control and command | |
349 | line editing. Only vi-style line editing commands have been | |
350 | standardized; emacs editing commands were left out due to | |
351 | objections. | |
352 | ||
b72432fd | 353 | A10) What is the bash `posix mode'? |
ccc6cda3 JA |
354 | |
355 | Although bash is an implementation of the POSIX.2 shell | |
356 | specification, there are areas where the bash default behavior | |
357 | differs from that spec. The bash `posix mode' changes the bash | |
358 | behavior in these areas so that it obeys the spec more closely. | |
359 | ||
360 | Posix mode is entered by starting bash with the --posix option or | |
361 | executing `set -o posix' after bash is running. | |
362 | ||
363 | The specific aspects of bash which change when posix mode is | |
364 | active are listed in the file CWRU/POSIX.NOTES in the bash | |
365 | distribution. They are also listed in a section in the Bash | |
366 | Reference Manual. | |
367 | ||
368 | Section B: The latest version | |
369 | ||
28ef6c31 | 370 | B1) What's new in version 2.05? |
bb70624e | 371 | |
28ef6c31 JA |
372 | Bash-2.05 contains the following new features (see the manual page for |
373 | complete descriptions and the CHANGES and NEWS files in the bash-2.05 | |
bb70624e JA |
374 | distribution): |
375 | ||
28ef6c31 JA |
376 | o This version has once again reverted to using locales and strcoll(3) when |
377 | processing pattern matching bracket expressions, as POSIX requires. | |
378 | o Added a new `--init-file' invocation argument as a synonym for `--rcfile', | |
379 | per the new GNU coding standards. | |
380 | o The /dev/tcp and /dev/udp redirections now accept service names as well as | |
381 | port numbers. | |
382 | o `complete' and `compgen' now take a `-o value' option, which controls some | |
383 | of the aspects of that compspec. Valid values are: | |
384 | ||
385 | default - perform bash default completion if programmable | |
386 | completion produces no matches | |
387 | dirnames - perform directory name completion if programmable | |
388 | completion produces no matches | |
389 | filenames - tell readline that the compspec produces filenames, | |
390 | so it can do things like append slashes to | |
391 | directory names and suppress trailing spaces | |
392 | o A new loadable builtin, realpath, which canonicalizes and expands symlinks | |
393 | in pathname arguments. | |
394 | o When `set' is called without options, it prints function defintions in a | |
395 | way that allows them to be reused as input. This affects `declare' and | |
396 | `declare -p' as well. This only happens when the shell is not in POSIX | |
397 | mode, since POSIX.2 forbids this behavior. | |
398 | ||
399 | A short feature history dating from bash-2.0: | |
400 | ||
401 | Bash-2.04 introduced the following new features: | |
402 | ||
bb70624e JA |
403 | o Programmable word completion with the new `complete' and `compgen' builtins; |
404 | examples are provided in examples/complete/complete-examples | |
405 | o `history' has a new `-d' option to delete a history entry | |
406 | o `bind' has a new `-x' option to bind key sequences to shell commands | |
407 | o The prompt expansion code has new `\j' and `\l' escape sequences | |
28ef6c31 | 408 | o The `no_empty_cmd_completion' shell option, if enabled, inhibits |
bb70624e JA |
409 | command completion when TAB is typed on an empty line |
410 | o `help' has a new `-s' option to print a usage synopsis | |
411 | o New arithmetic operators: var++, var--, ++var, --var, expr1,expr2 (comma) | |
412 | o New ksh93-style arithmetic for command: | |
413 | for ((expr1 ; expr2; expr3 )); do list; done | |
414 | o `read' has new options: `-t', `-n', `-d', `-s' | |
415 | o The redirection code handles several filenames specially: /dev/fd/N, | |
416 | /dev/stdin, /dev/stdout, /dev/stderr | |
417 | o The redirection code now recognizes /dev/tcp/HOST/PORT and | |
418 | /dev/udp/HOST/PORT and tries to open a TCP or UDP socket, respectively, | |
419 | to the specified port on the specified host | |
420 | o The ${!prefix*} expansion has been implemented | |
421 | o A new FUNCNAME variable, which expands to the name of a currently-executing | |
422 | function | |
423 | o The GROUPS variable is no longer readonly | |
424 | o A new shopt `xpg_echo' variable, to control the behavior of echo with | |
425 | respect to backslash-escape sequences at runtime | |
426 | o The NON_INTERACTIVE_LOGIN_SHELLS #define has returned | |
427 | ||
28ef6c31 | 428 | The version of Readline released with Bash-2.04, Readline-4.1, had several |
bb70624e JA |
429 | new features as well: |
430 | ||
431 | o Parentheses matching is always compiled into readline, and controllable | |
432 | with the new `blink-matching-paren' variable | |
433 | o The history-search-forward and history-search-backward functions now leave | |
434 | point at the end of the line when the search string is empty, like | |
435 | reverse-search-history, and forward-search-history | |
436 | o A new function for applications: rl_on_new_line_with_prompt() | |
437 | o New variables for applications: rl_already_prompted, and rl_gnu_readline_p | |
438 | ||
439 | ||
bb70624e | 440 | Bash-2.03 had very few new features, in keeping with the convention |
b72432fd JA |
441 | that odd-numbered releases provide mainly bug fixes. A number of new |
442 | features were added to Readline, mostly at the request of the Cygnus | |
443 | folks. | |
cce855bc | 444 | |
bb70624e | 445 | A new shopt option, `restricted_shell', so that startup files can test |
b72432fd | 446 | whether or not the shell was started in restricted mode |
bb70624e | 447 | Filename generation is now performed on the words between ( and ) in |
b72432fd JA |
448 | compound array assignments (this is really a bug fix) |
449 | OLDPWD is now auto-exported, as POSIX.2 requires | |
450 | ENV and BASH_ENV are read-only variables in a restricted shell | |
451 | Bash may now be linked against an already-installed Readline library, | |
452 | as long as the Readline library is version 4 or newer | |
453 | All shells begun with the `--login' option will source the login shell | |
454 | startup files, even if the shell is not interactive | |
455 | ||
bb70624e | 456 | There were lots of changes to the version of the Readline library released |
b72432fd JA |
457 | along with Bash-2.03. For a complete list of the changes, read the file |
458 | CHANGES in the Bash-2.03 distribution. | |
459 | ||
460 | Bash-2.02 contained the following new features: | |
d166f048 | 461 | |
cce855bc JA |
462 | a new version of malloc (based on the old GNU malloc code in previous |
463 | bash versions) that is more page-oriented, more conservative | |
464 | with memory usage, does not `orphan' large blocks when they | |
465 | are freed, is usable on 64-bit machines, and has allocation | |
466 | checking turned on unconditionally | |
467 | POSIX.2-style globbing character classes ([:alpha:], [:alnum:], etc.) | |
468 | POSIX.2-style globbing equivalence classes | |
469 | POSIX.2-style globbing collating symbols | |
470 | the ksh [[...]] extended conditional command | |
471 | the ksh egrep-style extended pattern matching operators | |
472 | a new `printf' builtin | |
473 | the ksh-like $(<filename) command substitution, which is equivalent to | |
474 | $(cat filename) | |
475 | new tilde prefixes that expand to directories from the directory stack | |
476 | new `**' arithmetic operator to do exponentiation | |
477 | case-insensitive globbing (filename expansion) | |
478 | menu completion a la tcsh | |
479 | `magic-space' history expansion function like tcsh | |
480 | the readline inputrc `language' has a new file inclusion directive ($include) | |
481 | ||
482 | Bash-2.01 contained only a few new features: | |
d166f048 JA |
483 | |
484 | new `GROUPS' builtin array variable containing the user's group list | |
485 | new bindable readline commands: history-and-alias-expand-line and | |
486 | alias-expand-line | |
ccc6cda3 | 487 | |
cce855bc | 488 | Bash-2.0 contained extensive changes and new features from bash-1.14.7. |
d166f048 | 489 | Here's a short list: |
ccc6cda3 JA |
490 | |
491 | new `time' reserved word to time pipelines, shell builtins, and | |
492 | shell functions | |
493 | one-dimensional arrays with a new compound assignment statement, | |
494 | appropriate expansion constructs and modifications to some | |
495 | of the builtins (read, declare, etc.) to use them | |
496 | new quoting syntaxes for ANSI-C string expansion and locale-specific | |
497 | string translation | |
498 | new expansions to do substring extraction, pattern replacement, and | |
499 | indirect variable expansion | |
500 | new builtins: `disown' and `shopt' | |
501 | new variables: HISTIGNORE, SHELLOPTS, PIPESTATUS, DIRSTACK, GLOBIGNORE, | |
502 | MACHTYPE, BASH_VERSINFO | |
503 | special handling of many unused or redundant variables removed | |
504 | (e.g., $notify, $glob_dot_filenames, $no_exit_on_failed_exec) | |
505 | dynamic loading of new builtin commands; many loadable examples provided | |
506 | new prompt expansions: \a, \e, \n, \H, \T, \@, \v, \V | |
507 | history and aliases available in shell scripts | |
508 | new readline variables: enable-keypad, mark-directories, input-meta, | |
509 | visible-stats, disable-completion, comment-begin | |
510 | new readline commands to manipulate the mark and operate on the region | |
511 | new readline emacs mode commands and bindings for ksh-88 compatibility | |
512 | updated and extended builtins | |
513 | new DEBUG trap | |
514 | expanded (and now documented) restricted shell mode | |
515 | ||
516 | implementation stuff: | |
517 | autoconf-based configuration | |
518 | nearly all of the bugs reported since version 1.14 have been fixed | |
519 | most builtins converted to use builtin `getopt' for consistency | |
520 | most builtins use -p option to display output in a reusable form | |
521 | (for consistency) | |
522 | grammar tighter and smaller (66 reduce-reduce conflicts gone) | |
523 | lots of code now smaller and faster | |
524 | test suite greatly expanded | |
525 | ||
28ef6c31 | 526 | B2) Are there any user-visible incompatibilities between bash-2.05 and |
ccc6cda3 JA |
527 | bash-1.14.7? |
528 | ||
28ef6c31 JA |
529 | There are a few incompatibilities between version 1.14.7 and version 2.05. |
530 | They are detailed in the file COMPAT in the bash-2.05 distribution. | |
ccc6cda3 JA |
531 | |
532 | Section C: Differences from other Unix shells | |
533 | ||
b72432fd | 534 | C1) How does bash differ from sh, the Bourne shell? |
ccc6cda3 JA |
535 | |
536 | This is a non-comprehensive list of features that differentiate bash | |
537 | from the SVR4.2 shell. The bash manual page explains these more | |
538 | completely. | |
539 | ||
540 | Things bash has that sh does not: | |
541 | long invocation options | |
542 | `!' reserved word to invert pipeline return value | |
543 | `time' reserved word to time pipelines and shell builtins | |
544 | the `function' reserved word | |
bb70624e JA |
545 | the `select' compound command and reserved word |
546 | arithmetic for command: for ((expr1 ; expr2; expr3 )); do list; done | |
ccc6cda3 JA |
547 | new $'...' and $"..." quoting |
548 | the $(...) form of command substitution | |
bc4cd23c JA |
549 | the $(<filename) form of command substitution, equivalent to |
550 | $(cat filename) | |
ccc6cda3 JA |
551 | the ${#param} parameter value length operator |
552 | the ${!param} indirect parameter expansion operator | |
bb70624e | 553 | the ${!param*} prefix expansion operator |
ccc6cda3 JA |
554 | the ${param:length[:offset]} parameter substring operator |
555 | the ${param/pat[/string]} parameter pattern substitution operator | |
556 | expansions to perform substring removal (${p%[%]w}, ${p#[#]w}) | |
557 | expansion of positional parameters beyond $9 with ${num} | |
558 | variables: BASH, BASH_VERSION, BASH_VERSINFO, UID, EUID, REPLY, | |
559 | TIMEFORMAT, PPID, PWD, OLDPWD, SHLVL, RANDOM, SECONDS, | |
560 | LINENO, HISTCMD, HOSTTYPE, OSTYPE, MACHTYPE, HOSTNAME, | |
561 | ENV, PS3, PS4, DIRSTACK, PIPESTATUS, HISTSIZE, HISTFILE, | |
bc4cd23c | 562 | HISTFILESIZE, HISTCONTROL, HISTIGNORE, GLOBIGNORE, GROUPS, |
ccc6cda3 | 563 | PROMPT_COMMAND, FCEDIT, FIGNORE, IGNOREEOF, INPUTRC, |
bb70624e JA |
564 | SHELLOPTS, OPTERR, HOSTFILE, TMOUT, FUNCNAME, histchars, |
565 | auto_resume | |
ccc6cda3 JA |
566 | DEBUG trap |
567 | variable arrays with new compound assignment syntax | |
568 | redirections: <>, &>, >| | |
569 | prompt string special char translation and variable expansion | |
bb70624e | 570 | auto-export of variables in initial environment |
ccc6cda3 JA |
571 | command search finds functions before builtins |
572 | bash return builtin will exit a file sourced with `.' | |
573 | builtins: cd -/-L/-P, exec -l/-c/-a, echo -e/-E, hash -p. | |
bb70624e JA |
574 | export -n/-f/-p/name=value, pwd -L/-P, |
575 | read -e/-p/-a/-t/-n/-d/-s, | |
ccc6cda3 JA |
576 | readonly -a/-f/name=value, trap -l, set +o, |
577 | set -b/-m/-o option/-h/-p/-B/-C/-H/-P, | |
578 | unset -f/-v, ulimit -m/-p/-u, | |
579 | type -a/-p/-t, suspend -f, kill -n, | |
580 | test -o optname/s1 == s2/s1 < s2/s1 > s2/-nt/-ot/-ef/-O/-G/-S | |
581 | bash reads ~/.bashrc for interactive shells, $ENV for non-interactive | |
582 | bash restricted shell mode is more extensive | |
583 | bash allows functions and variables with the same name | |
584 | brace expansion | |
585 | tilde expansion | |
586 | arithmetic expansion with $((...)) and `let' builtin | |
bc4cd23c | 587 | the `[[...]]' extended conditional command |
ccc6cda3 JA |
588 | process substitution |
589 | aliases and alias/unalias builtins | |
590 | local variables in functions and `local' builtin | |
bb70624e | 591 | readline and command-line editing with programmable completion |
ccc6cda3 JA |
592 | command history and history/fc builtins |
593 | csh-like history expansion | |
bb70624e JA |
594 | other new bash builtins: bind, command, compgen, complete, builtin, |
595 | declare/typeset, dirs, enable, fc, help, | |
596 | history, logout, popd, pushd, disown, shopt, | |
597 | printf | |
ccc6cda3 JA |
598 | exported functions |
599 | filename generation when using output redirection (command >a*) | |
bc4cd23c JA |
600 | POSIX.2-style globbing character classes |
601 | POSIX.2-style globbing equivalence classes | |
602 | POSIX.2-style globbing collating symbols | |
603 | egrep-like extended pattern matching operators | |
604 | case-insensitive pattern matching and globbing | |
ccc6cda3 JA |
605 | variable assignments preceding commands affect only that command, |
606 | even for builtins and functions | |
607 | posix mode | |
bb70624e JA |
608 | redirection to /dev/fd/N, /dev/stdin, /dev/stdout, /dev/stderr, |
609 | /dev/tcp/host/port, /dev/udp/host/port | |
ccc6cda3 JA |
610 | |
611 | Things sh has that bash does not: | |
612 | uses variable SHACCT to do shell accounting | |
613 | includes `stop' builtin (bash can use alias stop='kill -s STOP') | |
614 | `newgrp' builtin | |
615 | turns on job control if called as `jsh' | |
ccc6cda3 JA |
616 | $TIMEOUT (like bash $TMOUT) |
617 | `^' is a synonym for `|' | |
618 | new SVR4.2 sh builtins: mldmode, priv | |
619 | ||
620 | Implementation differences: | |
621 | redirection to/from compound commands causes sh to create a subshell | |
622 | bash does not allow unbalanced quotes; sh silently inserts them at EOF | |
623 | bash does not mess with signal 11 | |
624 | sh sets (euid, egid) to (uid, gid) if -p not supplied and uid < 100 | |
625 | bash splits only the results of expansions on IFS, using POSIX.2 | |
626 | field splitting rules; sh splits all words on IFS | |
627 | sh does not allow MAILCHECK to be unset (?) | |
628 | sh does not allow traps on SIGALRM or SIGCHLD | |
629 | bash allows multiple option arguments when invoked (e.g. -x -v); | |
630 | sh allows only a single option argument (`sh -x -v' attempts | |
d166f048 | 631 | to open a file named `-v', and, on SunOS 4.1.4, dumps core. |
b72432fd JA |
632 | On Solaris 2.4 and earlier versions, sh goes into an infinite |
633 | loop.) | |
ccc6cda3 JA |
634 | sh exits a script if any builtin fails; bash exits only if one of |
635 | the POSIX.2 `special' builtins fails | |
636 | ||
b72432fd | 637 | C2) How does bash differ from the Korn shell, version ksh88? |
ccc6cda3 JA |
638 | |
639 | Things bash has or uses that ksh88 does not: | |
640 | long invocation options | |
641 | `!' reserved word | |
bb70624e | 642 | arithmetic for command: for ((expr1 ; expr2; expr3 )); do list; done |
ccc6cda3 JA |
643 | posix mode and posix conformance |
644 | command hashing | |
645 | tilde expansion for assignment statements that look like $PATH | |
646 | process substitution with named pipes if /dev/fd is not available | |
647 | the ${!param} indirect parameter expansion operator | |
bb70624e | 648 | the ${!param*} prefix expansion operator |
ccc6cda3 JA |
649 | the ${param:length[:offset]} parameter substring operator |
650 | the ${param/pat[/string]} parameter pattern substitution operator | |
651 | variables: BASH, BASH_VERSION, BASH_VERSINFO, UID, EUID, SHLVL, | |
652 | TIMEFORMAT, HISTCMD, HOSTTYPE, OSTYPE, MACHTYPE, | |
653 | HISTFILESIZE, HISTIGNORE, HISTCONTROL, PROMPT_COMMAND, | |
654 | IGNOREEOF, FIGNORE, INPUTRC, HOSTFILE, DIRSTACK, | |
655 | PIPESTATUS, HOSTNAME, OPTERR, SHELLOPTS, GLOBIGNORE, | |
bb70624e | 656 | GROUPS, FUNCNAME, histchars, auto_resume |
ccc6cda3 JA |
657 | prompt expansion with backslash escapes and command substitution |
658 | redirection: &> (stdout and stderr) | |
bb70624e | 659 | more extensive and extensible editing and programmable completion |
ccc6cda3 JA |
660 | builtins: bind, builtin, command, declare, dirs, echo -e/-E, enable, |
661 | exec -l/-c/-a, fc -s, export -n/-f/-p, hash, help, history, | |
662 | jobs -x/-r/-s, kill -s/-n/-l, local, logout, popd, pushd, | |
bb70624e JA |
663 | read -e/-p/-a/-t/-n/-d/-s, readonly -a/-n/-f/-p, |
664 | set -o braceexpand/-o histexpand/-o interactive-comments/ | |
665 | -o notify/-o physical/-o posix/-o hashall/-o onecmd/ | |
666 | -h/-B/-C/-b/-H/-P, set +o, suspend, trap -l, type, | |
667 | typeset -a/-F/-p, ulimit -u, umask -S, alias -p, shopt, | |
668 | disown, printf, complete, compgen | |
ccc6cda3 | 669 | `!' csh-style history expansion |
bc4cd23c JA |
670 | POSIX.2-style globbing character classes |
671 | POSIX.2-style globbing equivalence classes | |
672 | POSIX.2-style globbing collating symbols | |
673 | egrep-like extended pattern matching operators | |
674 | case-insensitive pattern matching and globbing | |
675 | `**' arithmetic operator to do exponentiation | |
bb70624e | 676 | redirection to /dev/fd/N, /dev/stdin, /dev/stdout, /dev/stderr |
ccc6cda3 JA |
677 | |
678 | Things ksh88 has or uses that bash does not: | |
ccc6cda3 | 679 | tracked aliases |
bb70624e | 680 | variables: ERRNO, FPATH, EDITOR, VISUAL |
28ef6c31 | 681 | trap on ERR |
ccc6cda3 JA |
682 | co-processes (|&, >&p, <&p) |
683 | weirdly-scoped functions | |
684 | typeset +f to list all function names without definitions | |
685 | text of command history kept in a file, not memory | |
686 | builtins: alias -x, cd old new, fc -e -, newgrp, print, | |
687 | read -p/-s/-u/var?prompt, set -A/-o gmacs/ | |
688 | -o bgnice/-o markdirs/-o nolog/-o trackall/-o viraw/-s, | |
689 | typeset -H/-L/-R/-A/-ft/-fu/-fx/-l/-u/-t, whence | |
690 | ||
691 | Implementation differences: | |
692 | ksh runs last command of a pipeline in parent shell context | |
ccc6cda3 JA |
693 | bash has brace expansion by default (ksh88 compile-time option) |
694 | bash has fixed startup file for all interactive shells; ksh reads $ENV | |
695 | bash has exported functions | |
696 | bash command search finds functions before builtins | |
697 | ||
b72432fd | 698 | C3) Which new features in ksh-93 are not in bash, and which are? |
ccc6cda3 | 699 | |
28ef6c31 | 700 | New things in ksh-93 not in bash-2.05: |
ccc6cda3 JA |
701 | associative arrays |
702 | floating point arithmetic | |
ccc6cda3 JA |
703 | math library functions |
704 | ${!name[sub]} name of subscript for associative array | |
ccc6cda3 JA |
705 | `.' is allowed in variable names to create a hierarchical namespace |
706 | more extensive compound assignment syntax | |
707 | discipline functions | |
708 | `sleep' and `getconf' builtins (bash has loadable versions) | |
709 | typeset -n and `nameref' variables | |
710 | KEYBD trap | |
bb70624e JA |
711 | variables: .sh.edchar, .sh.edmode, .sh.edcol, .sh.edtext, .sh.version, |
712 | .sh.name, .sh.subscript, .sh.value, HISTEDIT | |
ccc6cda3 | 713 | backreferences in pattern matching |
bb70624e | 714 | print -f (bash uses printf) |
ccc6cda3 | 715 | `fc' has been renamed to `hist' |
ccc6cda3 | 716 | `.' can execute shell functions |
ccc6cda3 | 717 | |
bb70624e JA |
718 | New things in ksh-93 present in bash-2.04: |
719 | for (( expr1; expr2; expr3 )) ; do list; done - arithmetic for command | |
720 | ?:, ++, --, `expr1 , expr2' arithmetic operators | |
721 | expansions: ${!param}, ${param:offset[:len]}, ${param/pat[/str]}, | |
722 | ${!param*} | |
ccc6cda3 JA |
723 | compound array assignment |
724 | the `!' reserved word | |
725 | loadable builtins -- but ksh uses `builtin' while bash uses `enable' | |
726 | `command', `builtin', `disown' builtins | |
727 | new $'...' and $"..." quoting | |
728 | FIGNORE (but bash uses GLOBIGNORE), HISTCMD | |
729 | set -o notify/-C | |
730 | changes to kill builtin | |
731 | read -A (bash uses read -a) | |
bb70624e | 732 | read -t/-d |
ccc6cda3 JA |
733 | trap -p |
734 | exec -c/-a | |
735 | `.' restores the positional parameters when it completes | |
736 | POSIX.2 `test' | |
737 | umask -S | |
738 | unalias -a | |
739 | command and arithmetic substitution performed on PS1, PS4, and ENV | |
740 | command name completion | |
d166f048 | 741 | ENV processed only for interactive shells |
ccc6cda3 JA |
742 | |
743 | Section D: Why does bash do some things differently than other Unix shells? | |
744 | ||
b72432fd | 745 | D1) Why does bash run a different version of `command' than |
ccc6cda3 JA |
746 | `which command' says it will? |
747 | ||
b72432fd JA |
748 | On many systems, `which' is actually a csh script that assumes |
749 | you're running csh. In tcsh, `which' and its cousin `where' | |
750 | are builtins. On other Unix systems, `which' is a perl script | |
751 | that uses the PATH environment variable. | |
752 | ||
753 | The csh script version reads the csh startup files from your | |
754 | home directory and uses those to determine which `command' will | |
755 | be invoked. Since bash doesn't use any of those startup files, | |
756 | there's a good chance that your bash environment differs from | |
757 | your csh environment. The bash `type' builtin does everything | |
758 | `which' does, and will report correct results for the running | |
759 | shell. If you're really wedded to the name `which', try adding | |
760 | the following function definition to your .bashrc: | |
761 | ||
762 | which() | |
763 | { | |
bb70624e | 764 | builtin type "$@" |
b72432fd JA |
765 | } |
766 | ||
767 | If you're moving from tcsh and would like to bring `where' along | |
768 | as well, use this function: | |
769 | ||
770 | where() | |
771 | { | |
772 | builtin type -a "$@" | |
773 | } | |
ccc6cda3 | 774 | |
b72432fd | 775 | D2) Why doesn't bash treat brace expansions exactly like csh? |
ccc6cda3 JA |
776 | |
777 | The only difference between bash and csh brace expansion is that | |
778 | bash requires a brace expression to contain at least one unquoted | |
779 | comma if it is to be expanded. Any brace-surrounded word not | |
780 | containing an unquoted comma is left unchanged by the brace | |
781 | expansion code. This affords the greatest degree of sh | |
782 | compatibility. | |
783 | ||
784 | Bash, ksh, zsh, and pd-ksh all implement brace expansion this way. | |
785 | ||
b72432fd | 786 | D3) Why doesn't bash have csh variable modifiers? |
ccc6cda3 JA |
787 | |
788 | Posix has specified a more powerful, albeit somewhat more cryptic, | |
789 | mechanism cribbed from ksh, and bash implements it. | |
790 | ||
791 | ${parameter%word} | |
792 | Remove smallest suffix pattern. The WORD is expanded to produce | |
793 | a pattern. It then expands to the value of PARAMETER, with the | |
794 | smallest portion of the suffix matched by the pattern deleted. | |
795 | ||
796 | x=file.c | |
797 | echo ${x%.c}.o | |
798 | -->file.o | |
799 | ||
800 | ${parameter%%word} | |
801 | ||
802 | Remove largest suffix pattern. The WORD is expanded to produce | |
803 | a pattern. It then expands to the value of PARAMETER, with the | |
804 | largest portion of the suffix matched by the pattern deleted. | |
805 | ||
806 | x=posix/src/std | |
807 | echo ${x%%/*} | |
808 | -->posix | |
809 | ||
810 | ${parameter#word} | |
811 | Remove smallest prefix pattern. The WORD is expanded to produce | |
812 | a pattern. It then expands to the value of PARAMETER, with the | |
813 | smallest portion of the prefix matched by the pattern deleted. | |
814 | ||
815 | x=$HOME/src/cmd | |
816 | echo ${x#$HOME} | |
817 | -->/src/cmd | |
818 | ||
819 | ${parameter##word} | |
820 | Remove largest prefix pattern. The WORD is expanded to produce | |
821 | a pattern. It then expands to the value of PARAMETER, with the | |
822 | largest portion of the prefix matched by the pattern deleted. | |
823 | ||
824 | x=/one/two/three | |
825 | echo ${x##*/} | |
826 | -->three | |
827 | ||
828 | ||
829 | Given | |
830 | a=/a/b/c/d | |
831 | b=b.xxx | |
832 | ||
833 | csh bash result | |
834 | --- ---- ------ | |
835 | $a:h ${a%/*} /a/b/c | |
836 | $a:t ${a##*/} d | |
837 | $b:r ${b%.*} b | |
838 | $b:e ${b##*.} xxx | |
839 | ||
840 | ||
b72432fd | 841 | D4) How can I make my csh aliases work when I convert to bash? |
ccc6cda3 JA |
842 | |
843 | Bash uses a different syntax to support aliases than csh does. | |
844 | The details can be found in the documentation. We have provided | |
845 | a shell script which does most of the work of conversion for you; | |
28ef6c31 | 846 | this script can be found in ./examples/misc/aliasconv.sh. Here is |
ccc6cda3 JA |
847 | how you use it: |
848 | ||
849 | Start csh in the normal way for you. (e.g., `csh') | |
850 | ||
28ef6c31 | 851 | Pipe the output of `alias' through `aliasconv.sh', saving the |
ccc6cda3 JA |
852 | results into `bash_aliases': |
853 | ||
28ef6c31 | 854 | alias | bash aliasconv.sh >bash_aliases |
ccc6cda3 JA |
855 | |
856 | Edit `bash_aliases', carefully reading through any created | |
857 | functions. You will need to change the names of some csh specific | |
858 | variables to the bash equivalents. The script converts $cwd to | |
859 | $PWD, $term to $TERM, $home to $HOME, $user to $USER, and $prompt | |
860 | to $PS1. You may also have to add quotes to avoid unwanted | |
861 | expansion. | |
862 | ||
863 | For example, the csh alias: | |
864 | ||
865 | alias cd 'cd \!*; echo $cwd' | |
866 | ||
867 | is converted to the bash function: | |
868 | ||
869 | cd () { command cd "$@"; echo $PWD ; } | |
870 | ||
871 | The only thing that needs to be done is to quote $PWD: | |
872 | ||
873 | cd () { command cd "$@"; echo "$PWD" ; } | |
874 | ||
875 | Merge the edited file into your ~/.bashrc. | |
876 | ||
877 | There is an additional, more ambitious, script in | |
878 | examples/misc/cshtobash that attempts to convert your entire csh | |
879 | environment to its bash equivalent. This script can be run as | |
880 | simply `cshtobash' to convert your normal interactive | |
881 | environment, or as `cshtobash ~/.login' to convert your login | |
882 | environment. | |
883 | ||
b72432fd | 884 | D5) How can I pipe standard output and standard error from one command to |
ccc6cda3 JA |
885 | another, like csh does with `|&'? |
886 | ||
887 | Use | |
888 | command 2>&1 | command2 | |
889 | ||
890 | The key is to remember that piping is performed before redirection, so | |
891 | file descriptor 1 points to the pipe when it is duplicated onto file | |
892 | descriptor 2. | |
893 | ||
b72432fd | 894 | D6) Now that I've converted from ksh to bash, are there equivalents to |
ccc6cda3 JA |
895 | ksh features like autoloaded functions and the `whence' command? |
896 | ||
bb70624e JA |
897 | There are features in ksh-88 and ksh-93 that do not have direct bash |
898 | equivalents. Most, however, can be emulated with very little trouble. | |
ccc6cda3 JA |
899 | |
900 | ksh-88 feature Bash equivalent | |
901 | -------------- --------------- | |
ccc6cda3 JA |
902 | compiled-in aliases set up aliases in .bashrc; some ksh aliases are |
903 | bash builtins (hash, history, type) | |
ccc6cda3 JA |
904 | coprocesses named pipe pairs (one for read, one for write) |
905 | typeset +f declare -F | |
906 | cd, print, whence function substitutes in examples/functions/kshenv | |
907 | autoloaded functions examples/functions/autoload is the same as typeset -fu | |
908 | read var?prompt read -p prompt var | |
909 | ||
bb70624e JA |
910 | ksh-93 feature Bash equivalent |
911 | -------------- --------------- | |
912 | sleep, getconf Bash has loadable versions in examples/loadables | |
913 | ${.sh.version} $BASH_VERSION | |
914 | print -f printf | |
915 | hist alias fc=hist | |
916 | $HISTEDIT $FCEDIT | |
917 | ||
ccc6cda3 JA |
918 | Section E: How can I get bash to do certain things, and why does bash do |
919 | things the way it does? | |
920 | ||
b72432fd | 921 | E1) Why is the bash builtin `test' slightly different from /bin/test? |
ccc6cda3 JA |
922 | |
923 | The specific example used here is [ ! x -o x ], which is false. | |
924 | ||
925 | Bash's builtin `test' implements the Posix.2 spec, which can be | |
926 | summarized as follows (the wording is due to David Korn): | |
927 | ||
928 | Here is the set of rules for processing test arguments. | |
929 | ||
930 | 0 Args: False | |
931 | 1 Arg: True iff argument is not null. | |
932 | 2 Args: If first arg is !, True iff second argument is null. | |
933 | If first argument is unary, then true if unary test is true | |
934 | Otherwise error. | |
935 | 3 Args: If second argument is a binary operator, do binary test of $1 $3 | |
936 | If first argument is !, negate two argument test of $2 $3 | |
937 | If first argument is `(' and third argument is `)', do the | |
938 | one-argument test of the second argument. | |
939 | Otherwise error. | |
940 | 4 Args: If first argument is !, negate three argument test of $2 $3 $4. | |
941 | Otherwise unspecified | |
942 | 5 or more Args: unspecified. (Historical shells would use their | |
943 | current algorithm). | |
944 | ||
945 | The operators -a and -o are considered binary operators for the purpose | |
946 | of the 3 Arg case. | |
947 | ||
948 | As you can see, the test becomes (not (x or x)), which is false. | |
949 | ||
b72432fd | 950 | E2) Why does bash sometimes say `Broken pipe'? |
ccc6cda3 JA |
951 | |
952 | If a sequence of commands appears in a pipeline, and one of the | |
953 | reading commands finishes before the writer has finished, the | |
954 | writer receives a SIGPIPE signal. Many other shells special-case | |
955 | SIGPIPE as an exit status in the pipeline and do not report it. | |
956 | For example, in: | |
957 | ||
958 | ps -aux | head | |
959 | ||
960 | `head' can finish before `ps' writes all of its output, and ps | |
961 | will try to write on a pipe without a reader. In that case, bash | |
962 | will print `Broken pipe' to stderr when ps is killed by a | |
963 | SIGPIPE. | |
964 | ||
b72432fd JA |
965 | You can build a version of bash that will not report SIGPIPE errors |
966 | by uncommenting the definition of DONT_REPORT_SIGPIPE in the file | |
967 | config-top.h. | |
968 | ||
bb70624e | 969 | E3) When I have terminal escape sequences in my prompt, why does bash |
ccc6cda3 JA |
970 | wrap lines at the wrong column? |
971 | ||
972 | Readline, the line editing library that bash uses, does not know | |
973 | that the terminal escape sequences do not take up space on the | |
974 | screen. The redisplay code assumes, unless told otherwise, that | |
975 | each character in the prompt is a `printable' character that | |
976 | takes up one character position on the screen. | |
977 | ||
978 | You can use the bash prompt expansion facility (see the PROMPTING | |
979 | section in the manual page) to tell readline that sequences of | |
980 | characters in the prompt strings take up no screen space. | |
981 | ||
982 | Use the \[ escape to begin a sequence of non-printing characters, | |
983 | and the \] escape to signal the end of such a sequence. | |
984 | ||
bb70624e | 985 | E4) If I pipe the output of a command into `read variable', why doesn't |
ccc6cda3 JA |
986 | the output show up in $variable when the read command finishes? |
987 | ||
988 | This has to do with the parent-child relationship between Unix | |
28ef6c31 JA |
989 | processes. It affects all commands run in pipelines, not just |
990 | simple calls to `read'. For example, piping a command's output | |
991 | into a `while' loop that repeatedly calls `read' will result in | |
992 | the same behavior. | |
ccc6cda3 JA |
993 | |
994 | Each element of a pipeline runs in a separate process, a child of | |
995 | the shell running the pipeline. A subprocess cannot affect its | |
996 | parent's environment. When the `read' command sets the variable | |
997 | to the input, that variable is set only in the subshell, not the | |
998 | parent shell. When the subshell exits, the value of the variable | |
999 | is lost. | |
1000 | ||
1001 | Many pipelines that end with `read variable' can be converted | |
1002 | into command substitutions, which will capture the output of | |
1003 | a specified command. The output can then be assigned to a | |
1004 | variable: | |
1005 | ||
1006 | grep ^gnu /usr/lib/news/active | wc -l | read ngroup | |
1007 | ||
1008 | can be converted into | |
1009 | ||
1010 | ngroup=$(grep ^gnu /usr/lib/news/active | wc -l) | |
1011 | ||
1012 | This does not, unfortunately, work to split the text among | |
1013 | multiple variables, as read does when given multiple variable | |
1014 | arguments. If you need to do this, you can either use the | |
1015 | command substitution above to read the output into a variable | |
1016 | and chop up the variable using the bash pattern removal | |
1017 | expansion operators or use some variant of the following | |
1018 | approach. | |
1019 | ||
1020 | Say /usr/local/bin/ipaddr is the following shell script: | |
1021 | ||
1022 | #! /bin/sh | |
1023 | host `hostname` | awk '/address/ {print $NF}' | |
1024 | ||
1025 | Instead of using | |
1026 | ||
1027 | /usr/local/bin/ipaddr | read A B C D | |
1028 | ||
1029 | to break the local machine's IP address into separate octets, use | |
1030 | ||
1031 | OIFS="$IFS" | |
1032 | IFS=. | |
1033 | set -- $(/usr/local/bin/ipaddr) | |
1034 | IFS="$OIFS" | |
1035 | A="$1" B="$2" C="$3" D="$4" | |
1036 | ||
1037 | Beware, however, that this will change the shell's positional | |
1038 | parameters. If you need them, you should save them before doing | |
1039 | this. | |
1040 | ||
1041 | This is the general approach -- in most cases you will not need to | |
1042 | set $IFS to a different value. | |
1043 | ||
bb70624e | 1044 | E5) I have a bunch of shell scripts that use backslash-escaped characters |
ccc6cda3 JA |
1045 | in arguments to `echo'. Bash doesn't interpret these characters. Why |
1046 | not, and how can I make it understand them? | |
1047 | ||
1048 | This is the behavior of echo on most Unix System V machines. | |
1049 | ||
bb70624e | 1050 | The bash builtin `echo' is modeled after the 9th Edition |
ccc6cda3 JA |
1051 | Research Unix version of `echo'. It does not interpret |
1052 | backslash-escaped characters in its argument strings by default; | |
1053 | it requires the use of the -e option to enable the | |
1054 | interpretation. The System V echo provides no way to disable the | |
1055 | special characters; the bash echo has a -E option to disable | |
1056 | them. | |
1057 | ||
1058 | There is a configuration option that will make bash behave like | |
1059 | the System V echo and interpret things like `\t' by default. Run | |
1060 | configure with the --enable-usg-echo-default option to turn this | |
1061 | on. Be aware that this will cause some of the tests run when you | |
1062 | type `make tests' to fail. | |
1063 | ||
bb70624e JA |
1064 | There is a shell option, `xpg_echo', settable with `shopt' that will |
1065 | change the behavior of echo at runtime. Enabling this option turns | |
1066 | on expansion of backslash-escape sequences. | |
1067 | ||
1068 | E6) Why doesn't a while or for loop get suspended when I type ^Z? | |
ccc6cda3 JA |
1069 | |
1070 | This is a consequence of how job control works on Unix. The only | |
1071 | thing that can be suspended is the process group. This is a single | |
1072 | command or pipeline of commands that the shell forks and executes. | |
1073 | ||
1074 | When you run a while or for loop, the only thing that the shell forks | |
1075 | and executes are any commands in the while loop test and commands in | |
1076 | the loop bodies. These, therefore, are the only things that can be | |
1077 | suspended when you type ^Z. | |
1078 | ||
1079 | If you want to be able to stop the entire loop, you need to put it | |
1080 | within parentheses, which will force the loop into a subshell that | |
1081 | may be stopped (and subsequently restarted) as a single unit. | |
1082 | ||
28ef6c31 JA |
1083 | E7) What about empty for loops in Makefiles? |
1084 | ||
1085 | It's fairly common to see constructs like this in automatically-generated | |
1086 | Makefiles: | |
1087 | ||
1088 | SUBDIRS = @SUBDIRS@ | |
1089 | ||
1090 | ... | |
1091 | ||
1092 | subdirs-clean: | |
1093 | for d in ${SUBDIRS}; do \ | |
1094 | ( cd $$d && ${MAKE} ${MFLAGS} clean ) \ | |
1095 | done | |
1096 | ||
1097 | When SUBDIRS is empty, this results in a command like this being passed to | |
1098 | bash: | |
1099 | ||
1100 | for d in ; do | |
1101 | ( cd $d && ${MAKE} ${MFLAGS} clean ) | |
1102 | done | |
1103 | ||
1104 | This is a syntax error. If the reserved word `in' is present, a word must | |
1105 | follow it before the semicolon or newline. The language in the manual page | |
1106 | referring to the list of words being empty refers to the list after it is | |
1107 | expanded. There must be at least one word following the `in' when the | |
1108 | construct is parsed. | |
1109 | ||
1110 | The idiomatic Makefile solution is something like: | |
1111 | ||
1112 | SUBDIRS = @SUBDIRS@ | |
1113 | ||
1114 | subdirs-clean: | |
1115 | subdirs=$SUBDIRS ; for d in $$subdirs; do \ | |
1116 | ( cd $$d && ${MAKE} ${MFLAGS} clean ) \ | |
1117 | done | |
1118 | ||
1119 | ||
1120 | The POSIX.2 interpretation committee has considered this issue and declared | |
1121 | that the bash implemenation is correct, according to the standard: | |
1122 | ||
1123 | http://www.pasc.org/interps/unofficial/db/p1003.2/pasc-1003.2-169.html | |
1124 | ||
1125 | E8) Why does the arithmetic evaluation code complain about `08'? | |
1126 | ||
1127 | The bash arithmetic evaluation code (used for `let', $(()), (()), and in | |
1128 | other places), interprets a leading `0' in numeric constants as denoting | |
1129 | an octal number, and a leading `0x' as denoting hexadecimal. This is | |
1130 | in accordance with the POSIX.2 spec, section 2.9.2.1, which states that | |
1131 | arithmetic constants should be handled as signed long integers as defined | |
1132 | by the ANSI/ISO C standard. | |
1133 | ||
1134 | The POSIX.2 interpretation committee has confirmed this: | |
1135 | ||
1136 | http://www.pasc.org/interps/unofficial/db/p1003.2/pasc-1003.2-173.html | |
1137 | ||
1138 | E9) Why does the pattern matching expression [A-Z]* match files beginning | |
1139 | with every letter except `z'? | |
1140 | ||
1141 | Bash-2.05 and later versions have reverted to the bash-2.03 behavior of | |
1142 | honoring the current locale setting when processing ranges within pattern | |
1143 | matching bracket expressions ([A-Z]). This is what POSIX.2 and SUSv2/XPG5 | |
1144 | specify. | |
1145 | ||
1146 | The behavior of the matcher in bash-2.05 depends on the current LC_COLLATE | |
1147 | setting. Setting this variable to `C' or `POSIX' will result in the | |
1148 | traditional behavior ([A-Z] matches all uppercase ASCII characters). | |
1149 | Many other locales, including the en_US locale (the default on many US | |
1150 | versions of Linux) collate the upper and lower case letters like this: | |
1151 | ||
1152 | AaBb...Zz | |
1153 | ||
1154 | which means that [A-Z] matches every letter except `z'. | |
1155 | ||
1156 | The portable way to specify upper case letters is [:upper:] instead of | |
1157 | A-Z; lower case may be specified as [:lower:] instead of a-z. | |
1158 | ||
1159 | Look at the manual pages for setlocale(3), strcoll(3), and, if it is | |
1160 | present, locale(1). If you have locale(1), you can use it to find | |
1161 | your current locale information even if you do not have any of the | |
1162 | LC_ variables set. | |
1163 | ||
1164 | My advice is to put | |
1165 | ||
1166 | export LC_COLLATE=C | |
1167 | ||
1168 | into /etc/profile and inspect any shell scripts run from cron for | |
1169 | constructs like [A-Z]. This will prevent things like | |
1170 | ||
1171 | rm [A-Z]* | |
1172 | ||
1173 | from removing every file in the current directory except those beginning | |
1174 | with `z' and still allow individual users to change the collation order. | |
1175 | Users may put the above command into their own profiles as well, of course. | |
1176 | ||
ccc6cda3 JA |
1177 | Section F: Things to watch out for on certain Unix versions |
1178 | ||
b72432fd | 1179 | F1) Why can't I use command line editing in my `cmdtool'? |
ccc6cda3 JA |
1180 | |
1181 | The problem is `cmdtool' and bash fighting over the input. When | |
1182 | scrolling is enabled in a cmdtool window, cmdtool puts the tty in | |
1183 | `raw mode' to permit command-line editing using the mouse for | |
1184 | applications that cannot do it themselves. As a result, bash and | |
1185 | cmdtool each try to read keyboard input immediately, with neither | |
1186 | getting enough of it to be useful. | |
1187 | ||
1188 | This mode also causes cmdtool to not implement many of the | |
1189 | terminal functions and control sequences appearing in the | |
1190 | `sun-cmd' termcap entry. For a more complete explanation, see | |
1191 | that file examples/suncmd.termcap in the bash distribution. | |
1192 | ||
1193 | `xterm' is a better choice, and gets along with bash much more | |
1194 | smoothly. | |
1195 | ||
1196 | If you must use cmdtool, you can use the termcap description in | |
1197 | examples/suncmd.termcap. Set the TERMCAP variable to the terminal | |
1198 | description contained in that file, i.e. | |
1199 | ||
1200 | TERMCAP='Mu|sun-cmd:am:bs:km:pt:li#34:co#80:cl=^L:ce=\E[K:cd=\E[J:rs=\E[s:' | |
1201 | ||
1202 | Then export TERMCAP and start a new cmdtool window from that shell. | |
1203 | The bash command-line editing should behave better in the new | |
1204 | cmdtool. If this works, you can put the assignment to TERMCAP | |
1205 | in your bashrc file. | |
1206 | ||
b72432fd | 1207 | F2) I built bash on Solaris 2. Why do globbing expansions and filename |
ccc6cda3 JA |
1208 | completion chop off the first few characters of each filename? |
1209 | ||
1210 | This is the consequence of building bash on SunOS 5 and linking | |
1211 | with the libraries in /usr/ucblib, but using the definitions | |
1212 | and structures from files in /usr/include. | |
1213 | ||
1214 | The actual conflict is between the dirent structure in | |
1215 | /usr/include/dirent.h and the struct returned by the version of | |
1216 | `readdir' in libucb.a (a 4.3-BSD style `struct direct'). | |
1217 | ||
1218 | Make sure you've got /usr/ccs/bin ahead of /usr/ucb in your $PATH | |
1219 | when configuring and building bash. This will ensure that you | |
1220 | use /usr/ccs/bin/cc or acc instead of /usr/ucb/cc and that you | |
1221 | link with libc before libucb. | |
1222 | ||
1223 | If you have installed the Sun C compiler, you may also need to | |
1224 | put /usr/ccs/bin and /opt/SUNWspro/bin into your $PATH before | |
1225 | /usr/ucb. | |
1226 | ||
b72432fd | 1227 | F3) Why does bash dump core after I interrupt username completion or |
ccc6cda3 JA |
1228 | `~user' tilde expansion on a machine running NIS? |
1229 | ||
1230 | This is a famous and long-standing bug in the SunOS YP (sorry, NIS) | |
1231 | client library, which is part of libc. | |
1232 | ||
1233 | The YP library code keeps static state -- a pointer into the data | |
1234 | returned from the server. When YP initializes itself (setpwent), | |
1235 | it looks at this pointer and calls free on it if it's non-null. | |
1236 | So far, so good. | |
1237 | ||
1238 | If one of the YP functions is interrupted during getpwent (the | |
1239 | exact function is interpretwithsave()), and returns NULL, the | |
1240 | pointer is freed without being reset to NULL, and the function | |
1241 | returns. The next time getpwent is called, it sees that this | |
1242 | pointer is non-null, calls free, and the bash free() blows up | |
1243 | because it's being asked to free freed memory. | |
1244 | ||
1245 | The traditional Unix mallocs allow memory to be freed multiple | |
1246 | times; that's probably why this has never been fixed. You can | |
1247 | run configure with the `--without-gnu-malloc' option to use | |
1248 | the C library malloc and avoid the problem. | |
1249 | ||
b72432fd | 1250 | F4) I'm running SVR4.2. Why is the line erased every time I type `@'? |
ccc6cda3 JA |
1251 | |
1252 | The `@' character is the default `line kill' character in most | |
1253 | versions of System V, including SVR4.2. You can change this | |
1254 | character to whatever you want using `stty'. For example, to | |
1255 | change the line kill character to control-u, type | |
1256 | ||
1257 | stty kill ^U | |
1258 | ||
1259 | where the `^' and `U' can be two separate characters. | |
1260 | ||
b72432fd | 1261 | F5) Why does bash report syntax errors when my C News scripts use a |
ccc6cda3 JA |
1262 | redirection before a subshell command? |
1263 | ||
1264 | The actual command in question is something like | |
1265 | ||
1266 | < file ( command ) | |
1267 | ||
1268 | According to the grammar given in the POSIX.2 standard, this construct | |
1269 | is, in fact, a syntax error. Redirections may only precede `simple | |
1270 | commands'. A subshell construct such as the above is one of the shell's | |
1271 | `compound commands'. A redirection may only follow a compound command. | |
1272 | ||
bb70624e JA |
1273 | This affects the mechanical transformation of commands that use `cat' |
1274 | to pipe a file into a command (a favorite Useless-Use-Of-Cat topic on | |
1275 | comp.unix.shell). While most commands of the form | |
1276 | ||
1277 | cat file | command | |
1278 | ||
1279 | can be converted to `< file command', shell control structures such as | |
1280 | loops and subshells require `command < file'. | |
1281 | ||
28ef6c31 | 1282 | The file CWRU/sh-redir-hack in the bash-2.05 distribution is an |
ccc6cda3 JA |
1283 | (unofficial) patch to parse.y that will modify the grammar to |
1284 | support this construct. It will not apply with `patch'; you must | |
1285 | modify parse.y by hand. Note that if you apply this, you must | |
1286 | recompile with -DREDIRECTION_HACK. This introduces a large | |
1287 | number of reduce/reduce conflicts into the shell grammar. | |
1288 | ||
bb70624e JA |
1289 | F6) Why can't I use vi-mode editing on Red Hat Linux 6.1? |
1290 | ||
1291 | The short answer is that Red Hat screwed up. | |
1292 | ||
1293 | The long answer is that they shipped an /etc/inputrc that only works | |
1294 | for emacs mode editing, and then screwed all the vi users by setting | |
1295 | INPUTRC to /etc/inputrc in /etc/profile. | |
1296 | ||
1297 | The short fix is to do one of the following: remove or rename | |
1298 | /etc/inputrc, set INPUTRC=~/.inputrc in ~/.bashrc (or .bash_profile, | |
1299 | but make sure you export it if you do), remove the assignment to | |
1300 | INPUTRC from /etc/profile, add | |
1301 | ||
1302 | set keymap emacs | |
1303 | ||
1304 | to the beginning of /etc/inputrc, or bracket the key bindings in | |
1305 | /etc/inputrc with these lines | |
1306 | ||
1307 | $if mode=emacs | |
1308 | [...] | |
1309 | $endif | |
1310 | ||
1311 | Section G: How can I get bash to do certain common things? | |
1312 | ||
1313 | G1) How can I get bash to read and display eight-bit characters? | |
1314 | ||
1315 | This is a process requiring several steps. | |
1316 | ||
1317 | First, you must ensure that the `physical' data path is a full eight | |
1318 | bits. For xterms, for example, the `vt100' resources `eightBitInput' | |
1319 | and `eightBitOutput' should be set to `true'. | |
1320 | ||
1321 | Once you have set up an eight-bit path, you must tell the kernel and | |
1322 | tty driver to leave the eighth bit of characters alone when processing | |
1323 | keyboard input. Use `stty' to do this: | |
1324 | ||
1325 | stty cs8 -istrip -parenb | |
1326 | ||
1327 | For old BSD-style systems, you can use | |
1328 | ||
1329 | stty pass8 | |
1330 | ||
1331 | You may also need | |
1332 | ||
1333 | stty even odd | |
1334 | ||
1335 | Finally, you need to tell readline that you will be inputting and | |
1336 | displaying eight-bit characters. You use readline variables to do | |
1337 | this. These variables can be set in your .inputrc or using the bash | |
1338 | `bind' builtin. Here's an example using `bind': | |
1339 | ||
1340 | bash$ bind 'set convert-meta off' | |
1341 | bash$ bind 'set meta-flag on' | |
1342 | bash$ bind 'set output-meta on' | |
1343 | ||
1344 | The `set' commands between the single quotes may also be placed | |
1345 | in ~/.inputrc. | |
1346 | ||
1347 | G2) How do I write a function `x' to replace builtin command `x', but | |
1348 | still invoke the command from within the function? | |
1349 | ||
1350 | This is why the `command' and `builtin' builtins exist. The | |
1351 | `command' builtin executes the command supplied as its first | |
1352 | argument, skipping over any function defined with that name. The | |
1353 | `builtin' builtin executes the builtin command given as its first | |
1354 | argument directly. | |
1355 | ||
1356 | For example, to write a function to replace `cd' that writes the | |
1357 | hostname and current directory to an xterm title bar, use | |
1358 | something like the following: | |
1359 | ||
1360 | cd() | |
1361 | { | |
1362 | builtin cd "$@" && xtitle "$HOST: $PWD" | |
1363 | } | |
1364 | ||
1365 | This could also be written using `command' instead of `builtin'; | |
1366 | the version above is marginally more efficient. | |
1367 | ||
1368 | G3) How can I find the value of a shell variable whose name is the value | |
1369 | of another shell variable? | |
1370 | ||
1371 | Versions of Bash newer than Bash-2.0 support this directly. You can use | |
1372 | ||
1373 | ${!var} | |
1374 | ||
1375 | For example, the following sequence of commands will echo `z': | |
1376 | ||
1377 | var1=var2 | |
1378 | var2=z | |
1379 | echo ${!var1} | |
1380 | ||
1381 | For sh compatibility, use the `eval' builtin. The important | |
1382 | thing to remember is that `eval' expands the arguments you give | |
1383 | it again, so you need to quote the parts of the arguments that | |
1384 | you want `eval' to act on. | |
1385 | ||
1386 | For example, this expression prints the value of the last positional | |
1387 | parameter: | |
1388 | ||
1389 | eval echo \"\$\{$#\}\" | |
1390 | ||
1391 | The expansion of the quoted portions of this expression will be | |
1392 | deferred until `eval' runs, while the `$#' will be expanded | |
1393 | before `eval' is executed. In versions of bash later than bash-2.0, | |
1394 | ||
1395 | echo ${!#} | |
1396 | ||
1397 | does the same thing. | |
1398 | ||
1399 | G4) How can I make the bash `time' reserved word print timing output that | |
1400 | looks like the output from my system's /usr/bin/time? | |
1401 | ||
1402 | The bash command timing code looks for a variable `TIMEFORMAT' and | |
1403 | uses its value as a format string to decide how to display the | |
1404 | timing statistics. | |
1405 | ||
1406 | The value of TIMEFORMAT is a string with `%' escapes expanded in a | |
1407 | fashion similar in spirit to printf(3). The manual page explains | |
1408 | the meanings of the escape sequences in the format string. | |
1409 | ||
1410 | If TIMEFORMAT is not set, bash acts as if the following assignment had | |
1411 | been performed: | |
1412 | ||
1413 | TIMEFORMAT=$'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS' | |
1414 | ||
1415 | The POSIX.2 default time format (used by `time -p command') is | |
1416 | ||
1417 | TIMEFORMAT=$'real %2R\nuser %2U\nsys %2S' | |
1418 | ||
1419 | The BSD /usr/bin/time format can be emulated with: | |
1420 | ||
1421 | TIMEFORMAT=$'\t%1R real\t%1U user\t%1S sys' | |
1422 | ||
1423 | The System V /usr/bin/time format can be emulated with: | |
1424 | ||
1425 | TIMEFORMAT=$'\nreal\t%1R\nuser\t%1U\nsys\t%1S' | |
1426 | ||
1427 | The ksh format can be emulated with: | |
1428 | ||
1429 | TIMEFORMAT=$'\nreal\t%2lR\nuser\t%2lU\nsys\t%2lS' | |
1430 | ||
1431 | G5) How do I get the current directory into my prompt? | |
1432 | ||
1433 | Bash provides a number of backslash-escape sequences which are expanded | |
1434 | when the prompt string (PS1 or PS2) is displayed. The full list is in | |
1435 | the manual page. | |
1436 | ||
1437 | The \w expansion gives the full pathname of the current directory, with | |
1438 | a tilde (`~') substituted for the current value of $HOME. The \W | |
1439 | expansion gives the basename of the current directory. To put the full | |
1440 | pathname of the current directory into the path without any tilde | |
1441 | subsitution, use $PWD. Here are some examples: | |
1442 | ||
1443 | PS1='\w$ ' # current directory with tilde | |
1444 | PS1='\W$ ' # basename of current directory | |
1445 | PS1='$PWD$ ' # full pathname of current directory | |
1446 | ||
1447 | The single quotes are important in the final example to prevent $PWD from | |
1448 | being expanded when the assignment to PS1 is performed. | |
1449 | ||
1450 | G6) How can I rename "*.foo" to "*.bar"? | |
1451 | ||
1452 | Use the pattern removal functionality described in D3. The following `for' | |
1453 | loop will do the trick: | |
1454 | ||
1455 | for f in *.foo; do | |
1456 | mv $f ${f%foo}bar | |
1457 | done | |
1458 | ||
1459 | G7) How can I translate a filename from uppercase to lowercase? | |
1460 | ||
1461 | The script examples/functions/lowercase, originally written by John DuBois, | |
1462 | will do the trick. The converse is left as an exercise. | |
1463 | ||
1464 | G8) How can I write a filename expansion (globbing) pattern that will match | |
1465 | all files in the current directory except "." and ".."? | |
1466 | ||
1467 | You must have set the `extglob' shell option using `shopt -s extglob' to use | |
1468 | this: | |
1469 | ||
1470 | echo .!(.|) * | |
1471 | ||
1472 | A solution that works without extended globbing is given in the Unix Shell | |
1473 | FAQ, posted periodically to comp.unix.shell. | |
1474 | ||
1475 | Section H: Where do I go from here? | |
ccc6cda3 | 1476 | |
bb70624e | 1477 | H1) How do I report bugs in bash, and where should I look for fixes and |
ccc6cda3 JA |
1478 | advice? |
1479 | ||
1480 | Use the `bashbug' script to report bugs. It is built and | |
1481 | installed at the same time as bash. It provides a standard | |
1482 | template for reporting a problem and automatically includes | |
1483 | information about your configuration and build environment. | |
1484 | ||
b72432fd | 1485 | `bashbug' sends its reports to bug-bash@gnu.org, which |
ccc6cda3 JA |
1486 | is a large mailing list gatewayed to the usenet newsgroup gnu.bash.bug. |
1487 | ||
1488 | Bug fixes, answers to questions, and announcements of new releases | |
1489 | are all posted to gnu.bash.bug. Discussions concerning bash features | |
1490 | and problems also take place there. | |
1491 | ||
1492 | To reach the bash maintainers directly, send mail to | |
b72432fd | 1493 | bash-maintainers@gnu.org. |
ccc6cda3 | 1494 | |
bb70624e | 1495 | H2) What kind of bash documentation is there? |
ccc6cda3 JA |
1496 | |
1497 | First, look in the doc directory in the bash distribution. It should | |
1498 | contain at least the following files: | |
1499 | ||
1500 | bash.1 an extensive, thorough Unix-style manual page | |
1501 | builtins.1 a manual page covering just bash builtin commands | |
b72432fd JA |
1502 | bashref.texi a reference manual in GNU tex`info format |
1503 | bashref.info an info version of the reference manual | |
ccc6cda3 JA |
1504 | FAQ this file |
1505 | article.ms text of an article written for The Linux Journal | |
1506 | readline.3 a man page describing readline | |
1507 | ||
b72432fd JA |
1508 | Postscript, HTML, and ASCII files created from the above source are |
1509 | available in the documentation distribution. | |
ccc6cda3 JA |
1510 | |
1511 | There is additional documentation available for anonymous FTP from host | |
cce855bc | 1512 | ftp.cwru.edu in the `pub/bash' directory. |
ccc6cda3 JA |
1513 | |
1514 | Cameron Newham and Bill Rosenblatt have written a book on bash, published | |
1515 | by O'Reilly and Associates. The book is based on Bill Rosenblatt's Korn | |
d166f048 JA |
1516 | Shell book. The title is ``Learning the Bash Shell'', and the ISBN number |
1517 | is 1-56592-147-X. Look for it in fine bookstores near you. This book | |
1518 | covers bash-1.14, but has an appendix describing some of the new features | |
cce855bc JA |
1519 | in bash-2.0. |
1520 | ||
bc4cd23c | 1521 | A second edition of this book is available, published in January, 1998. |
cce855bc JA |
1522 | The ISBN number is 1-56592-347-2. Look for it in the same fine bookstores |
1523 | or on the web. | |
ccc6cda3 | 1524 | |
bb70624e | 1525 | H3) What's coming in future versions? |
ccc6cda3 JA |
1526 | |
1527 | These are features I plan to include in a future version of bash. | |
1528 | ||
28ef6c31 | 1529 | a bash debugger (a minimally-tested version is included with bash-2.05) |
bb70624e | 1530 | associative arrays |
28ef6c31 JA |
1531 | changes to the DEBUG trap to be compatible with ksh93 (which runs the |
1532 | trap before each simple command, instead of after each one like previous | |
1533 | versions) | |
1534 | an implementation of the ksh-like ERR trap | |
ccc6cda3 | 1535 | |
bb70624e | 1536 | H4) What's on the bash `wish list' for future versions? |
ccc6cda3 JA |
1537 | |
1538 | These are features that may or may not appear in a future version of bash. | |
1539 | ||
ccc6cda3 | 1540 | breaking some of the shell functionality into embeddable libraries |
bb70624e | 1541 | a module system like zsh's, using dynamic loading like builtins |
ccc6cda3 JA |
1542 | better internationalization using GNU `gettext' |
1543 | an option to use external files for the long `help' text | |
cce855bc | 1544 | date-stamped command history |
bb70624e JA |
1545 | a bash programmer's guide with a chapter on creating loadable builtins |
1546 | a better loadable interface to perl with access to the shell builtins and | |
1547 | variables (contributions gratefully accepted) | |
ccc6cda3 | 1548 | |
bb70624e | 1549 | H5) When will the next release appear? |
ccc6cda3 | 1550 | |
28ef6c31 | 1551 | The next version will appear sometime in 2001 or 2002. Never make |
cce855bc | 1552 | predictions. |
ccc6cda3 JA |
1553 | |
1554 | ||
28ef6c31 | 1555 | This document is Copyright 1995-2001 by Chester Ramey. |
ccc6cda3 JA |
1556 | |
1557 | Permission is hereby granted, without written agreement and | |
1558 | without license or royalty fees, to use, copy, and distribute | |
1559 | this document for any purpose, provided that the above copyright | |
1560 | notice appears in all copies of this document and that the | |
1561 | contents of this document remain unaltered. |