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1 | Compatibility with previous versions |
2 | ==================================== | |
3 | ||
0628567a | 4 | This document details the incompatibilities between this version of bash, |
a0c0a00f CR |
5 | bash-4.4, and the previous widely-available versions, bash-3.x (which is |
6 | still the `standard' version for Mac OS X), 4.1/4.2 (which are still | |
7 | standard on a few Linux distributions), and bash-4.3, the current | |
ac50fbac CR |
8 | widely-available version. These were discovered by users of bash-2.x |
9 | through 4.x, so this list is not comprehensive. Some of these | |
10 | incompatibilities occur between the current version and versions 2.0 and | |
11 | above. | |
b80f6443 JA |
12 | |
13 | 1. Bash uses a new quoting syntax, $"...", to do locale-specific | |
ccc6cda3 JA |
14 | string translation. Users who have relied on the (undocumented) |
15 | behavior of bash-1.14 will have to change their scripts. For | |
16 | instance, if you are doing something like this to get the value of | |
17 | a variable whose name is the value of a second variable: | |
18 | ||
19 | eval var2=$"$var1" | |
20 | ||
21 | you will have to change to a different syntax. | |
22 | ||
23 | This capability is directly supported by bash-2.0: | |
24 | ||
25 | var2=${!var1} | |
26 | ||
27 | This alternate syntax will work portably between bash-1.14 and bash-2.0: | |
28 | ||
29 | eval var2=\$${var1} | |
30 | ||
31 | 2. One of the bugs fixed in the YACC grammar tightens up the rules | |
32 | concerning group commands ( {...} ). The `list' that composes the | |
33 | body of the group command must be terminated by a newline or | |
34 | semicolon. That's because the braces are reserved words, and are | |
35 | recognized as such only when a reserved word is legal. This means | |
36 | that while bash-1.14 accepted shell function definitions like this: | |
37 | ||
38 | foo() { : } | |
39 | ||
40 | bash-2.0 requires this: | |
41 | ||
42 | foo() { :; } | |
43 | ||
44 | This is also an issue for commands like this: | |
45 | ||
46 | mkdir dir || { echo 'could not mkdir' ; exit 1; } | |
47 | ||
48 | The syntax required by bash-2.0 is also accepted by bash-1.14. | |
49 | ||
50 | 3. The options to `bind' have changed to make them more consistent with | |
51 | the rest of the bash builtins. If you are using `bind -d' to list | |
7117c2d2 JA |
52 | the readline key bindings in a form that can be re-read, use `bind -p' |
53 | instead. If you were using `bind -v' to list the key bindings, use | |
ccc6cda3 JA |
54 | `bind -P' instead. |
55 | ||
56 | 4. The `long' invocation options must now be prefixed by `--' instead | |
57 | of `-'. (The old form is still accepted, for the time being.) | |
58 | ||
59 | 5. There was a bug in the version of readline distributed with bash-1.14 | |
60 | that caused it to write badly-formatted key bindings when using | |
61 | `bind -d'. The only key sequences that were affected are C-\ (which | |
62 | should appear as \C-\\ in a key binding) and C-" (which should appear | |
63 | as \C-\"). If these key sequences appear in your inputrc, as, for | |
64 | example, | |
65 | ||
66 | "\C-\": self-insert | |
67 | ||
68 | they will need to be changed to something like the following: | |
69 | ||
70 | "\C-\\": self-insert | |
71 | ||
7117c2d2 | 72 | 6. A number of people complained about having to use ESC to terminate an |
b72432fd JA |
73 | incremental search, and asked for an alternate mechanism. Bash-2.03 |
74 | uses the value of the settable readline variable `isearch-terminators' | |
75 | to decide which characters should terminate an incremental search. If | |
76 | that variable has not been set, ESC and Control-J will terminate a | |
77 | search. | |
ccc6cda3 JA |
78 | |
79 | 7. Some variables have been removed: MAIL_WARNING, notify, history_control, | |
80 | command_oriented_history, glob_dot_filenames, allow_null_glob_expansion, | |
81 | nolinks, hostname_completion_file, noclobber, no_exit_on_failed_exec, and | |
82 | cdable_vars. Most of them are now implemented with the new `shopt' | |
d166f048 JA |
83 | builtin; others were already implemented by `set'. Here is a list of |
84 | correspondences: | |
85 | ||
86 | MAIL_WARNING shopt mailwarn | |
87 | notify set -o notify | |
88 | history_control HISTCONTROL | |
89 | command_oriented_history shopt cmdhist | |
90 | glob_dot_filenames shopt dotglob | |
91 | allow_null_glob_expansion shopt nullglob | |
92 | nolinks set -o physical | |
93 | hostname_completion_file HOSTFILE | |
94 | noclobber set -o noclobber | |
95 | no_exit_on_failed_exec shopt execfail | |
96 | cdable_vars shopt cdable_vars | |
97 | ||
98 | 8. `ulimit' now sets both hard and soft limits and reports the soft limit | |
99 | by default (when neither -H nor -S is specified). This is compatible | |
100 | with versions of sh and ksh that implement `ulimit'. The bash-1.14 | |
101 | behavior of, for example, | |
102 | ||
103 | ulimit -c 0 | |
104 | ||
105 | can be obtained with | |
106 | ||
107 | ulimit -S -c 0 | |
108 | ||
109 | It may be useful to define an alias: | |
110 | ||
111 | alias ulimit="ulimit -S" | |
ccc6cda3 | 112 | |
cce855bc JA |
113 | 9. Bash-2.01 uses a new quoting syntax, $'...' to do ANSI-C string |
114 | translation. Backslash-escaped characters in ... are expanded and | |
115 | replaced as specified by the ANSI C standard. | |
116 | ||
117 | 10. The sourcing of startup files has changed somewhat. This is explained | |
118 | more completely in the INVOCATION section of the manual page. | |
119 | ||
120 | A non-interactive shell not named `sh' and not in posix mode reads | |
121 | and executes commands from the file named by $BASH_ENV. A | |
122 | non-interactive shell started by `su' and not in posix mode will read | |
123 | startup files. No other non-interactive shells read any startup files. | |
124 | ||
125 | An interactive shell started in posix mode reads and executes commands | |
126 | from the file named by $ENV. | |
b72432fd JA |
127 | |
128 | 11. The <> redirection operator was changed to conform to the POSIX.2 spec. | |
129 | In the absence of any file descriptor specification preceding the `<>', | |
130 | file descriptor 0 is used. In bash-1.14, this was the behavior only | |
131 | when in POSIX mode. The bash-1.14 behavior may be obtained with | |
132 | ||
133 | <>filename 1>&0 | |
bb70624e JA |
134 | |
135 | 12. The `alias' builtin now checks for invalid options and takes a `-p' | |
136 | option to display output in POSIX mode. If you have old aliases beginning | |
137 | with `-' or `+', you will have to add the `--' to the alias command | |
138 | that declares them: | |
139 | ||
140 | alias -x='chmod a-x' --> alias -- -x='chmod a-x' | |
28ef6c31 | 141 | |
f73dda09 | 142 | 13. The behavior of range specificiers within bracket matching expressions |
28ef6c31 JA |
143 | in the pattern matcher (e.g., [A-Z]) depends on the current locale, |
144 | specifically the value of the LC_COLLATE environment variable. Setting | |
145 | this variable to C or POSIX will result in the traditional ASCII behavior | |
146 | for range comparisons. If the locale is set to something else, e.g., | |
147 | en_US (specified by the LANG or LC_ALL variables), collation order is | |
148 | locale-dependent. For example, the en_US locale sorts the upper and | |
149 | lower case letters like this: | |
150 | ||
151 | AaBb...Zz | |
152 | ||
153 | so a range specification like [A-Z] will match every letter except `z'. | |
7117c2d2 JA |
154 | Other locales collate like |
155 | ||
156 | aAbBcC...zZ | |
157 | ||
158 | which means that [A-Z] matches every letter except `a'. | |
28ef6c31 JA |
159 | |
160 | The portable way to specify upper case letters is [:upper:] instead of | |
161 | A-Z; lower case may be specified as [:lower:] instead of a-z. | |
162 | ||
163 | Look at the manual pages for setlocale(3), strcoll(3), and, if it is | |
164 | present, locale(1). | |
165 | ||
166 | You can find your current locale information by running locale(1): | |
167 | ||
168 | caleb.ins.cwru.edu(2)$ locale | |
169 | LANG=en_US | |
170 | LC_CTYPE="en_US" | |
171 | LC_NUMERIC="en_US" | |
172 | LC_TIME="en_US" | |
173 | LC_COLLATE="en_US" | |
174 | LC_MONETARY="en_US" | |
175 | LC_MESSAGES="en_US" | |
176 | LC_ALL=en_US | |
177 | ||
178 | My advice is to put | |
179 | ||
180 | export LC_COLLATE=C | |
181 | ||
182 | into /etc/profile and inspect any shell scripts run from cron for | |
183 | constructs like [A-Z]. This will prevent things like | |
184 | ||
185 | rm [A-Z]* | |
186 | ||
187 | from removing every file in the current directory except those beginning | |
188 | with `z' and still allow individual users to change the collation order. | |
189 | Users may put the above command into their own profiles as well, of course. | |
190 | ||
0628567a JA |
191 | 14. Bash versions up to 1.14.7 included an undocumented `-l' operator to |
192 | the `test/[' builtin. It was a unary operator that expanded to the | |
193 | length of its string argument. This let you do things like | |
28ef6c31 JA |
194 | |
195 | test -l $variable -lt 20 | |
196 | ||
0628567a | 197 | for example. |
28ef6c31 | 198 | |
0628567a JA |
199 | This was included for backwards compatibility with old versions of the |
200 | Bourne shell, which did not provide an easy way to obtain the length of | |
201 | the value of a shell variable. | |
28ef6c31 | 202 | |
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203 | This operator is not part of the POSIX standard, because one can (and |
204 | should) use ${#variable} to get the length of a variable's value. | |
205 | Bash-2.x does not support it. | |
f73dda09 | 206 | |
0628567a JA |
207 | 15. Bash no longer auto-exports the HOME, PATH, SHELL, TERM, HOSTNAME, |
208 | HOSTTYPE, MACHTYPE, or OSTYPE variables. If they appear in the initial | |
209 | environment, the export attribute will be set, but if bash provides a | |
210 | default value, they will remain local to the current shell. | |
f73dda09 | 211 | |
0628567a JA |
212 | 16. Bash no longer initializes the FUNCNAME, GROUPS, or DIRSTACK variables |
213 | to have special behavior if they appear in the initial environment. | |
f73dda09 | 214 | |
0628567a JA |
215 | 17. Bash no longer removes the export attribute from the SSH_CLIENT or |
216 | SSH2_CLIENT variables, and no longer attempts to discover whether or | |
217 | not it has been invoked by sshd in order to run the startup files. | |
b80f6443 | 218 | |
0628567a JA |
219 | 18. Bash no longer requires that the body of a function be a group command; |
220 | any compound command is accepted. | |
95732b49 | 221 | |
0628567a JA |
222 | 19. As of bash-3.0, the pattern substitution operators no longer perform |
223 | quote removal on the pattern before attempting the match. This is the | |
224 | way the pattern removal functions behave, and is more consistent. | |
95732b49 | 225 | |
0628567a JA |
226 | 20. After bash-3.0 was released, I reimplemented tilde expansion, incorporating |
227 | it into the mainline word expansion code. This fixes the bug that caused | |
228 | the results of tilde expansion to be re-expanded. There is one | |
229 | incompatibility: a ${paramOPword} expansion within double quotes will not | |
230 | perform tilde expansion on WORD. This is consistent with the other | |
231 | expansions, and what POSIX specifies. | |
232 | ||
233 | 21. A number of variables have the integer attribute by default, so the += | |
234 | assignment operator returns expected results: RANDOM, LINENO, MAILCHECK, | |
235 | HISTCMD, OPTIND. | |
236 | ||
237 | 22. Bash-3.x is much stricter about $LINENO correctly reflecting the line | |
238 | number in a script; assignments to LINENO have little effect. | |
239 | ||
240 | 23. By default, readline binds the terminal special characters to their | |
241 | readline equivalents. As of bash-3.1/readline-5.1, this is optional and | |
242 | controlled by the bind-tty-special-chars readline variable. | |
243 | ||
244 | 24. The \W prompt string expansion abbreviates $HOME as `~'. The previous | |
245 | behavior is available with ${PWD##/*/}. | |
246 | ||
247 | 25. The arithmetic exponentiation operator is right-associative as of bash-3.1. | |
248 | ||
249 | 26. The rules concerning valid alias names are stricter, as per POSIX.2. | |
250 | ||
251 | 27. The Readline key binding functions now obey the convert-meta setting active | |
252 | when the binding takes place, as the dispatch code does when characters | |
253 | are read and processed. | |
254 | ||
255 | 28. The historical behavior of `trap' reverting signal disposition to the | |
256 | original handling in the absence of a valid first argument is implemented | |
257 | only if the first argument is a valid signal number. | |
258 | ||
259 | 29. In versions of bash after 3.1, the ${parameter//pattern/replacement} | |
260 | expansion does not interpret `%' or `#' specially. Those anchors don't | |
261 | have any real meaning when replacing every match. | |
262 | ||
263 | 30. Beginning with bash-3.1, the combination of posix mode and enabling the | |
264 | `xpg_echo' option causes echo to ignore all options, not looking for `-n' | |
265 | ||
266 | 31. Beginning with bash-3.2, bash follows the Bourne-shell-style (and POSIX- | |
267 | style) rules for parsing the contents of old-style backquoted command | |
268 | substitutions. Previous versions of bash attempted to recursively parse | |
269 | embedded quoted strings and shell constructs; bash-3.2 uses strict POSIX | |
270 | rules to find the closing backquote and simply passes the contents of the | |
271 | command substitution to a subshell for parsing and execution. | |
272 | ||
273 | 32. Beginning with bash-3.2, bash uses access(2) when executing primaries for | |
274 | the test builtin and the [[ compound command, rather than looking at the | |
275 | file permission bits obtained with stat(2). This obeys restrictions of | |
276 | the file system (e.g., read-only or noexec mounts) not available via stat. | |
277 | ||
3185942a JA |
278 | 33. Bash-3.2 adopts the convention used by other string and pattern matching |
279 | operators for the `[[' compound command, and matches any quoted portion | |
280 | of the right-hand-side argument to the =~ operator as a string rather | |
281 | than a regular expression. | |
282 | ||
283 | 34. Bash-4.0 allows the behavior in the previous item to be modified using | |
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284 | the notion of a shell `compatibility level'. If the compat31 shopt |
285 | option is set, quoting the pattern has no special effect. | |
3185942a JA |
286 | |
287 | 35. Bash-3.2 (patched) and Bash-4.0 fix a bug that leaves the shell in an | |
288 | inconsistent internal state following an assignment error. One of the | |
289 | changes means that compound commands or { ... } grouping commands are | |
290 | aborted under some circumstances in which they previously were not. | |
291 | This is what Posix specifies. | |
292 | ||
293 | 36. Bash-4.0 now allows process substitution constructs to pass unchanged | |
294 | through brace expansion, so any expansion of the contents will have to be | |
295 | separately specified, and each process subsitution will have to be | |
296 | separately entered. | |
297 | ||
298 | 37. Bash-4.0 now allows SIGCHLD to interrupt the wait builtin, as Posix | |
299 | specifies, so the SIGCHLD trap is no longer always invoked once per | |
495aee44 CR |
300 | exiting child if you are using `wait' to wait for all children. As |
301 | of bash-4.2, this is the status quo only when in posix mode. | |
3185942a JA |
302 | |
303 | 38. Since bash-4.0 now follows Posix rules for finding the closing delimiter | |
304 | of a $() command substitution, it will not behave as previous versions | |
305 | did, but will catch more syntax and parsing errors before spawning a | |
306 | subshell to evaluate the command substitution. | |
307 | ||
308 | 39. The programmable completion code uses the same set of delimiting characters | |
309 | as readline when breaking the command line into words, rather than the | |
310 | set of shell metacharacters, so programmable completion and readline | |
311 | should be more consistent. | |
312 | ||
313 | 40. When the read builtin times out, it attempts to assign any input read to | |
314 | specified variables, which also causes variables to be set to the empty | |
315 | string if there is not enough input. Previous versions discarded the | |
316 | characters read. | |
317 | ||
318 | 41. Beginning with bash-4.0, when one of the commands in a pipeline is killed | |
319 | by a SIGINT while executing a command list, the shell acts as if it | |
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320 | received the interrupt. This can be disabled by setting the compat31 or |
321 | compat32 shell options. | |
17345e5a JA |
322 | |
323 | 42. Bash-4.0 changes the handling of the set -e option so that the shell exits | |
324 | if a pipeline fails (and not just if the last command in the failing | |
325 | pipeline is a simple command). This is not as Posix specifies. There is | |
326 | work underway to update this portion of the standard; the bash-4.0 | |
327 | behavior attempts to capture the consensus at the time of release. | |
0001803f CR |
328 | |
329 | 43. Bash-4.0 fixes a Posix mode bug that caused the . (source) builtin to | |
330 | search the current directory for its filename argument, even if "." is | |
331 | not in $PATH. Posix says that the shell shouldn't look in $PWD in this | |
332 | case. | |
333 | ||
334 | 44. Bash-4.1 uses the current locale when comparing strings using the < and | |
335 | > operators to the `[[' command. This can be reverted to the previous | |
495aee44 CR |
336 | behavior (ASCII collating and strcmp(3)) by setting one of the |
337 | `compatNN' shopt options, where NN is less than 41. | |
338 | ||
ac50fbac CR |
339 | 45. Bash-4.1 conforms to the current Posix specification for `set -u': |
340 | expansions of $@ and $* when there are no positional parameters do not | |
341 | cause the shell to exit. | |
342 | ||
343 | 46. Bash-4.1 implements the current Posix specification for `set -e' and | |
344 | exits when any command fails, not just a simple command or pipeline. | |
345 | ||
346 | 47. Command substitutions now remove the caller's trap strings when trap is | |
495aee44 CR |
347 | run to set a new trap in the subshell. Previous to bash-4.2, the old |
348 | trap strings persisted even though the actual signal handlers were reset. | |
349 | ||
ac50fbac | 350 | 48. When in Posix mode, a single quote is not treated specially in a |
495aee44 CR |
351 | double-quoted ${...} expansion, unless the expansion operator is |
352 | # or % or the new `//', `^', or `,' expansions. In particular, it | |
353 | does not define a new quoting context. This is from Posix interpretation | |
354 | 221. | |
355 | ||
ac50fbac | 356 | 49. Posix mode shells no longer exit if a variable assignment error occurs |
495aee44 CR |
357 | with an assignment preceding a command that is not a special builtin. |
358 | ||
ac50fbac CR |
359 | 50. Bash-4.2 attempts to preserve what the user typed when performing word |
360 | completion, instead of, for instance, expanding shell variable | |
361 | references to their value. | |
362 | ||
363 | 51. When in Posix mode, bash-4.2 exits if the filename supplied as an argument | |
364 | to `.' is not found and the shell is not interactive. | |
365 | ||
366 | 52. When compiled for strict Posix compatibility, bash-4.3 does not enable | |
367 | history expansion by default in interactive shells, since it results in | |
368 | a non-conforming environment. | |
369 | ||
370 | 53. Bash-4.3 runs the replacement string in the pattern substitution word | |
371 | expansion through quote removal. The code already treats quote | |
372 | characters in the replacement string as special; if it treats them as | |
373 | special, then quote removal should remove them. | |
0001803f | 374 | |
a0c0a00f CR |
375 | 54. Bash-4.4 no longer considers a reference to ${a[@]} or ${a[*]}, where `a' |
376 | is an array without any elements set, to be a reference to an unset | |
377 | variable. This means that such a reference will not cause the shell to | |
378 | exit when the `-u' option is enabled. | |
379 | ||
380 | 55. Bash-4.4 allows double quotes to quote the history expansion character (!) | |
381 | when in Posix mode, since Posix specifies the effects of double quotes. | |
382 | ||
383 | 56. Bash-4.4 does not inherit $PS4 from the environment if running as root. | |
384 | ||
385 | 57. Bash-4.4 doesn't allow a `break' or `continue' in a function to affect | |
386 | loop execution in the calling context. | |
387 | ||
388 | 58. Bash-4.4 no longer expands tildes in $PATH elements when in Posix mode. | |
389 | ||
390 | 59. Bash-4.4 does not attempt to perform a compound array assignment if an | |
391 | argument to `declare' or a similar builtin expands to a word that looks | |
392 | like a compound array assignment (e.g. declare w=$x where x='(foo)'). | |
393 | ||
0001803f CR |
394 | Shell Compatibility Level |
395 | ========================= | |
396 | ||
397 | Bash-4.0 introduced the concept of a `shell compatibility level', specified | |
ac50fbac CR |
398 | as a set of options to the shopt builtin (compat31, compat32, compat40, |
399 | compat41, and compat42 at this writing). There is only one current | |
400 | compatibility level -- each option is mutually exclusive. This list does not | |
401 | mention behavior that is standard for a particular version (e.g., setting | |
402 | compat32 means that quoting the rhs of the regexp matching operator quotes | |
403 | special regexp characters in the word, which is default behavior in bash-3.2 | |
404 | and above). | |
405 | ||
406 | Bash-4.3 introduces a new shell variable: BASH_COMPAT. The value assigned | |
407 | to this variable (a decimal version number like 4.2, or an integer | |
408 | corresponding to the compatNN option, like 42) determines the compatibility | |
409 | level. | |
0001803f | 410 | |
a0c0a00f CR |
411 | Bash-4.4 has begun deprecating older compatibility levels. Eventually, the |
412 | options will be removed in favor of the BASH_COMPAT variable. | |
413 | ||
0001803f CR |
414 | compat31 set |
415 | - the < and > operators to the [[ command do not consider the current | |
495aee44 | 416 | locale when comparing strings; they use ASCII ordering |
0001803f CR |
417 | - quoting the rhs of the regexp matching operator (=~) has no |
418 | special effect | |
419 | ||
420 | compat32 set | |
421 | - the < and > operators to the [[ command do not consider the current | |
495aee44 | 422 | locale when comparing strings; they use ASCII ordering |
0001803f CR |
423 | |
424 | compat40 set | |
425 | - the < and > operators to the [[ command do not consider the current | |
495aee44 | 426 | locale when comparing strings; they use ASCII ordering |
0001803f | 427 | - interrupting a command list such as "a ; b ; c" causes the execution |
495aee44 CR |
428 | of the entire list to be aborted (in versions before bash-4.0, |
429 | interrupting one command in a list caused the next to be executed) | |
0001803f | 430 | |
495aee44 CR |
431 | compat41 set |
432 | - interrupting a command list such as "a ; b ; c" causes the execution | |
a0c0a00f | 433 | of the entire list to be aborted (in versions before bash-4.0, |
495aee44 CR |
434 | interrupting one command in a list caused the next to be executed) |
435 | - when in posix mode, single quotes in the `word' portion of a | |
436 | double-quoted parameter expansion define a new quoting context and | |
437 | are treated specially | |
ac50fbac CR |
438 | |
439 | compat42 set | |
440 | - the replacement string in double-quoted pattern substitution is not | |
441 | run through quote removal, as in previous versions | |
a0c0a00f CR |
442 | |
443 | compat43 set | |
444 | - the shell does not print a warning message if an attempt is made to | |
445 | use a quoted compound assignment as an argument to declare | |
446 | (declare -a foo='(1 2)') | |
447 | - word expansion errors are considered non-fatal errors that cause the | |
448 | current command to fail, even in Posix mode | |
449 | - when executing a shell function, the loop state (while/until/etc.) is | |
450 | not reset, so `break' or `continue' in a shell function will break or | |
451 | continue loops in the calling context. Bash-4.4 and later reset the | |
452 | loop state to prevent this. | |
453 | ||
0001803f CR |
454 | ------------------------------------------------------------------------------- |
455 | ||
456 | Copying and distribution of this file, with or without modification, | |
457 | are permitted in any medium without royalty provided the copyright | |
458 | notice and this notice are preserved. This file is offered as-is, | |
459 | without any warranty. |