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1 | Compatibility with previous versions |
2 | ==================================== | |
3 | ||
0628567a | 4 | This document details the incompatibilities between this version of bash, |
8868edaf | 5 | bash-5.1, and the previous widely-available versions, bash-3.2 (which is |
d233b485 | 6 | still the `standard' version for Mac OS X), 4.2/4.3 (which are still |
8868edaf CR |
7 | standard on a few Linux distributions), and bash-4.4/bash-5.0, the current |
8 | widely-available versions. These were discovered by users of bash-2.x | |
9 | through 5.x, so this list is not comprehensive. Some of these | |
ac50fbac CR |
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 | |
0628567a JA |
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 | |
0001803f CR |
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 | |
8868edaf | 295 | separately specified, and each process substitution will have to be |
3185942a JA |
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 | |
0001803f CR |
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 | ||
d233b485 CR |
394 | 60. Bash-5.0 only sets up BASH_ARGV and BASH_ARGC at startup if extended |
395 | debugging mode is active. The old behavior of unconditionally setting | |
396 | BASH_ARGC and BASH_ARGV is available at compatibility levels less than | |
397 | or equal to 44. | |
398 | ||
399 | 61. Bash-5.0 doesn't allow a `break' or `continue' in a subshell to attempt | |
400 | to break or continue loop execution inherited from the calling context. | |
401 | ||
402 | 62. Bash-5.0 doesn't allow variable assignments preceding builtins like | |
403 | export and readonly to modify variables with the same name in preceding | |
404 | contexts (including the global context) unless the shell is in posix | |
405 | mode, since export and readonly are special builtins. | |
406 | ||
8868edaf CR |
407 | 63. Bash-5.1 changes the way posix-mode shells handle assignment statements |
408 | preceding shell function calls. Previous versions of POSIX specified that | |
409 | such assignments would persist after the function returned; subsequent | |
410 | versions of the standard removed that requirement (interpretation #654). | |
411 | Bash-5.1 posix mode assignment statements preceding shell function calls | |
412 | do not persist after the function returns. | |
413 | ||
414 | 64. Bash-5.1 reverts to the bash-4.4 treatment of pathname expansion of words | |
415 | containing backslashes but no other special globbing characters. This comes | |
416 | after a protracted discussion and a POSIX interpretation (#1234). | |
417 | ||
418 | 65. In bash-5.1, disabling posix mode attempts to restore the state of several | |
419 | options that posix mode modifies to the state they had before enabling | |
420 | posix mode. Previous versions restored these options to default values. | |
421 | ||
d233b485 | 422 | |
0001803f CR |
423 | Shell Compatibility Level |
424 | ========================= | |
425 | ||
426 | Bash-4.0 introduced the concept of a `shell compatibility level', specified | |
8868edaf CR |
427 | as a set of options to the shopt builtin (compat31, compat32, compat40, |
428 | compat41, and so on). There is only one current compatibility level -- | |
429 | each option is mutually exclusive. The compatibility level is intended to | |
430 | allow users to select behavior from previous versions that is incompatible | |
431 | with newer versions while they migrate scripts to use current features and | |
432 | behavior. It's intended to be a temporary solution. | |
433 | ||
434 | This section does not mention behavior that is standard for a particular | |
435 | version (e.g., setting compat32 means that quoting the rhs of the regexp | |
436 | matching operator quotes special regexp characters in the word, which is | |
437 | default behavior in bash-3.2 and above). | |
438 | ||
439 | If a user enables, say, compat32, it may affect the behavior of other | |
440 | compatibility levels up to and including the current compatibility level. | |
441 | The idea is that each compatibility level controls behavior that changed in | |
442 | that version of bash, but that behavior may have been present in earlier | |
443 | versions. For instance, the change to use locale-based comparisons with | |
444 | the `[[' command came in bash-4.1, and earlier versions used ASCII-based | |
445 | comparisons, so enabling compat32 will enable ASCII-based comparisons as | |
446 | well. That granularity may not be sufficient for all uses, and as a result | |
447 | users should employ compatibility levels carefully. Read the documentation | |
448 | for a particular feature to find out the current behavior. | |
449 | ||
450 | Bash-4.3 introduced a new shell variable: BASH_COMPAT. The value assigned | |
ac50fbac CR |
451 | to this variable (a decimal version number like 4.2, or an integer |
452 | corresponding to the compatNN option, like 42) determines the compatibility | |
453 | level. | |
0001803f | 454 | |
8868edaf CR |
455 | Starting with bash-4.4, bash has begun deprecating older compatibility |
456 | levels. Eventually, the options will be removed in favor of the | |
457 | BASH_COMPAT variable. | |
a0c0a00f | 458 | |
8868edaf CR |
459 | Bash-5.0 is the final version for which there will be an individual shopt |
460 | option for the previous version. Users should use the BASH_COMPAT variable | |
461 | on bash-5.0 and later versions. | |
462 | ||
463 | The following table describes the behavior changes controlled by each | |
464 | compatibility level setting. The `compatNN' tag is used as shorthand for | |
465 | setting the compatibility level to NN using one of the following | |
466 | mechanisms. For versions prior to bash-5.0, the compatibility level may be | |
467 | set using the corresponding compatNN shopt option. For bash-4.3 and later | |
468 | versions, the BASH_COMPAT variable is preferred, and it is required for | |
469 | bash-5.1 and later versions. | |
0001803f | 470 | |
8868edaf | 471 | compat31 |
0001803f | 472 | - the < and > operators to the [[ command do not consider the current |
495aee44 | 473 | locale when comparing strings; they use ASCII ordering |
8868edaf CR |
474 | - quoting the rhs of the [[ command's regexp matching operator (=~) |
475 | has no special effect | |
0001803f | 476 | |
8868edaf | 477 | compat32 |
0001803f | 478 | - the < and > operators to the [[ command do not consider the current |
495aee44 | 479 | locale when comparing strings; they use ASCII ordering |
0001803f | 480 | - interrupting a command list such as "a ; b ; c" causes the execution |
8868edaf CR |
481 | of the next command in the list (in bash-4.0 and later versions, |
482 | the shell acts as if it received the interrupt, so interrupting | |
483 | one command in a list aborts the execution of the entire list) | |
0001803f | 484 | |
8868edaf CR |
485 | compat40 |
486 | - the < and > operators to the [[ command do not consider the current | |
487 | locale when comparing strings; they use ASCII ordering. | |
488 | Bash versions prior to bash-4.1 use ASCII collation and strcmp(3); | |
489 | bash-4.1 and later use the current locale's collation sequence and | |
490 | strcoll(3). | |
491 | ||
492 | compat41 | |
493 | - in posix mode, `time' may be followed by options and still be | |
494 | recognized as a reserved word (this is POSIX interpretation 267) | |
495 | - in posix mode, the parser requires that an even number of single | |
496 | quotes occur in the `word' portion of a double-quoted ${...} | |
497 | parameter expansion and treats them specially, so that characters | |
498 | within the single quotes are considered quoted (this is POSIX | |
499 | interpretation 221) | |
500 | ||
501 | compat42 | |
ac50fbac | 502 | - the replacement string in double-quoted pattern substitution is not |
8868edaf CR |
503 | run through quote removal, as it is in versions after bash-4.2 |
504 | - in posix mode, single quotes are considered special when expanding | |
505 | the `word' portion of a double-quoted ${...} parameter expansion | |
506 | and can be used to quote a closing brace or other special character | |
507 | (this is part of POSIX interpretation 221); in later versions, | |
508 | single quotes are not special within double-quoted word expansions | |
509 | ||
510 | compat43 | |
a0c0a00f CR |
511 | - the shell does not print a warning message if an attempt is made to |
512 | use a quoted compound assignment as an argument to declare | |
8868edaf CR |
513 | (declare -a foo='(1 2)'). Later versions warn that this usage is |
514 | deprecated. | |
a0c0a00f | 515 | - word expansion errors are considered non-fatal errors that cause the |
8868edaf CR |
516 | current command to fail, even in posix mode (the default behavior is |
517 | to make them fatal errors that cause the shell to exit) | |
d233b485 CR |
518 | - when executing a shell function, the loop state (while/until/etc.) |
519 | is not reset, so `break' or `continue' in that function will break | |
520 | or continue loops in the calling context. Bash-4.4 and later reset | |
8868edaf | 521 | the loop state to prevent this |
d233b485 | 522 | |
8868edaf | 523 | compat44 |
d233b485 CR |
524 | - the shell sets up the values used by BASH_ARGV and BASH_ARGC so |
525 | they can expand to the shell's positional parameters even if extended | |
526 | debug mode is not enabled | |
8868edaf CR |
527 | - a subshell inherits loops from its parent context, so `break' |
528 | or `continue' will cause the subshell to exit. Bash-5.0 and later | |
529 | reset the loop state to prevent the exit | |
d233b485 CR |
530 | - variable assignments preceding builtins like export and readonly |
531 | that set attributes continue to affect variables with the same | |
532 | name in the calling environment even if the shell is not in posix | |
533 | mode | |
534 | ||
8868edaf CR |
535 | compat50 (set using BASH_COMPAT) |
536 | - Bash-5.1 changed the way $RANDOM is generated to introduce slightly | |
537 | more randomness. If the shell compatibility level is set to 50 or | |
538 | lower, it reverts to the method from bash-5.0 and previous versions, | |
539 | so seeding the random number generator by assigning a value to | |
540 | RANDOM will produce the same sequence as in bash-5.0 | |
541 | - If the command hash table is empty, bash versions prior to bash-5.1 | |
542 | printed an informational message to that effect even when writing | |
543 | output in a format that can be reused as input (-l). Bash-5.1 | |
544 | suppresses that message if -l is supplied | |
545 | ||
a0c0a00f | 546 | |
0001803f CR |
547 | ------------------------------------------------------------------------------- |
548 | ||
549 | Copying and distribution of this file, with or without modification, | |
550 | are permitted in any medium without royalty provided the copyright | |
551 | notice and this notice are preserved. This file is offered as-is, | |
552 | without any warranty. |