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0628567a | 1 | This document details the incompatibilities between this version of bash, |
3185942a | 2 | bash-4.0, and the previous widely-available versions, bash-1.14 (which is |
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3 | still the `standard' version for a few Linux distributions) and bash-2.x. |
4 | These were discovered by users of bash-2.x and 3.x, so this list is not | |
5 | comprehensive. Some of these incompatibilities occur between the current | |
6 | version and versions 2.0 and above. (The differences between bash-1.14 and | |
7 | bash-2.0 were significant.) | |
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8 | |
9 | 1. Bash uses a new quoting syntax, $"...", to do locale-specific | |
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10 | string translation. Users who have relied on the (undocumented) |
11 | behavior of bash-1.14 will have to change their scripts. For | |
12 | instance, if you are doing something like this to get the value of | |
13 | a variable whose name is the value of a second variable: | |
14 | ||
15 | eval var2=$"$var1" | |
16 | ||
17 | you will have to change to a different syntax. | |
18 | ||
19 | This capability is directly supported by bash-2.0: | |
20 | ||
21 | var2=${!var1} | |
22 | ||
23 | This alternate syntax will work portably between bash-1.14 and bash-2.0: | |
24 | ||
25 | eval var2=\$${var1} | |
26 | ||
27 | 2. One of the bugs fixed in the YACC grammar tightens up the rules | |
28 | concerning group commands ( {...} ). The `list' that composes the | |
29 | body of the group command must be terminated by a newline or | |
30 | semicolon. That's because the braces are reserved words, and are | |
31 | recognized as such only when a reserved word is legal. This means | |
32 | that while bash-1.14 accepted shell function definitions like this: | |
33 | ||
34 | foo() { : } | |
35 | ||
36 | bash-2.0 requires this: | |
37 | ||
38 | foo() { :; } | |
39 | ||
40 | This is also an issue for commands like this: | |
41 | ||
42 | mkdir dir || { echo 'could not mkdir' ; exit 1; } | |
43 | ||
44 | The syntax required by bash-2.0 is also accepted by bash-1.14. | |
45 | ||
46 | 3. The options to `bind' have changed to make them more consistent with | |
47 | the rest of the bash builtins. If you are using `bind -d' to list | |
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48 | the readline key bindings in a form that can be re-read, use `bind -p' |
49 | instead. If you were using `bind -v' to list the key bindings, use | |
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50 | `bind -P' instead. |
51 | ||
52 | 4. The `long' invocation options must now be prefixed by `--' instead | |
53 | of `-'. (The old form is still accepted, for the time being.) | |
54 | ||
55 | 5. There was a bug in the version of readline distributed with bash-1.14 | |
56 | that caused it to write badly-formatted key bindings when using | |
57 | `bind -d'. The only key sequences that were affected are C-\ (which | |
58 | should appear as \C-\\ in a key binding) and C-" (which should appear | |
59 | as \C-\"). If these key sequences appear in your inputrc, as, for | |
60 | example, | |
61 | ||
62 | "\C-\": self-insert | |
63 | ||
64 | they will need to be changed to something like the following: | |
65 | ||
66 | "\C-\\": self-insert | |
67 | ||
7117c2d2 | 68 | 6. A number of people complained about having to use ESC to terminate an |
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69 | incremental search, and asked for an alternate mechanism. Bash-2.03 |
70 | uses the value of the settable readline variable `isearch-terminators' | |
71 | to decide which characters should terminate an incremental search. If | |
72 | that variable has not been set, ESC and Control-J will terminate a | |
73 | search. | |
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74 | |
75 | 7. Some variables have been removed: MAIL_WARNING, notify, history_control, | |
76 | command_oriented_history, glob_dot_filenames, allow_null_glob_expansion, | |
77 | nolinks, hostname_completion_file, noclobber, no_exit_on_failed_exec, and | |
78 | cdable_vars. Most of them are now implemented with the new `shopt' | |
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79 | builtin; others were already implemented by `set'. Here is a list of |
80 | correspondences: | |
81 | ||
82 | MAIL_WARNING shopt mailwarn | |
83 | notify set -o notify | |
84 | history_control HISTCONTROL | |
85 | command_oriented_history shopt cmdhist | |
86 | glob_dot_filenames shopt dotglob | |
87 | allow_null_glob_expansion shopt nullglob | |
88 | nolinks set -o physical | |
89 | hostname_completion_file HOSTFILE | |
90 | noclobber set -o noclobber | |
91 | no_exit_on_failed_exec shopt execfail | |
92 | cdable_vars shopt cdable_vars | |
93 | ||
94 | 8. `ulimit' now sets both hard and soft limits and reports the soft limit | |
95 | by default (when neither -H nor -S is specified). This is compatible | |
96 | with versions of sh and ksh that implement `ulimit'. The bash-1.14 | |
97 | behavior of, for example, | |
98 | ||
99 | ulimit -c 0 | |
100 | ||
101 | can be obtained with | |
102 | ||
103 | ulimit -S -c 0 | |
104 | ||
105 | It may be useful to define an alias: | |
106 | ||
107 | alias ulimit="ulimit -S" | |
ccc6cda3 | 108 | |
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109 | 9. Bash-2.01 uses a new quoting syntax, $'...' to do ANSI-C string |
110 | translation. Backslash-escaped characters in ... are expanded and | |
111 | replaced as specified by the ANSI C standard. | |
112 | ||
113 | 10. The sourcing of startup files has changed somewhat. This is explained | |
114 | more completely in the INVOCATION section of the manual page. | |
115 | ||
116 | A non-interactive shell not named `sh' and not in posix mode reads | |
117 | and executes commands from the file named by $BASH_ENV. A | |
118 | non-interactive shell started by `su' and not in posix mode will read | |
119 | startup files. No other non-interactive shells read any startup files. | |
120 | ||
121 | An interactive shell started in posix mode reads and executes commands | |
122 | from the file named by $ENV. | |
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123 | |
124 | 11. The <> redirection operator was changed to conform to the POSIX.2 spec. | |
125 | In the absence of any file descriptor specification preceding the `<>', | |
126 | file descriptor 0 is used. In bash-1.14, this was the behavior only | |
127 | when in POSIX mode. The bash-1.14 behavior may be obtained with | |
128 | ||
129 | <>filename 1>&0 | |
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130 | |
131 | 12. The `alias' builtin now checks for invalid options and takes a `-p' | |
132 | option to display output in POSIX mode. If you have old aliases beginning | |
133 | with `-' or `+', you will have to add the `--' to the alias command | |
134 | that declares them: | |
135 | ||
136 | alias -x='chmod a-x' --> alias -- -x='chmod a-x' | |
28ef6c31 | 137 | |
f73dda09 | 138 | 13. The behavior of range specificiers within bracket matching expressions |
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139 | in the pattern matcher (e.g., [A-Z]) depends on the current locale, |
140 | specifically the value of the LC_COLLATE environment variable. Setting | |
141 | this variable to C or POSIX will result in the traditional ASCII behavior | |
142 | for range comparisons. If the locale is set to something else, e.g., | |
143 | en_US (specified by the LANG or LC_ALL variables), collation order is | |
144 | locale-dependent. For example, the en_US locale sorts the upper and | |
145 | lower case letters like this: | |
146 | ||
147 | AaBb...Zz | |
148 | ||
149 | so a range specification like [A-Z] will match every letter except `z'. | |
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150 | Other locales collate like |
151 | ||
152 | aAbBcC...zZ | |
153 | ||
154 | which means that [A-Z] matches every letter except `a'. | |
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155 | |
156 | The portable way to specify upper case letters is [:upper:] instead of | |
157 | A-Z; lower case may be specified as [:lower:] instead of a-z. | |
158 | ||
159 | Look at the manual pages for setlocale(3), strcoll(3), and, if it is | |
160 | present, locale(1). | |
161 | ||
162 | You can find your current locale information by running locale(1): | |
163 | ||
164 | caleb.ins.cwru.edu(2)$ locale | |
165 | LANG=en_US | |
166 | LC_CTYPE="en_US" | |
167 | LC_NUMERIC="en_US" | |
168 | LC_TIME="en_US" | |
169 | LC_COLLATE="en_US" | |
170 | LC_MONETARY="en_US" | |
171 | LC_MESSAGES="en_US" | |
172 | LC_ALL=en_US | |
173 | ||
174 | My advice is to put | |
175 | ||
176 | export LC_COLLATE=C | |
177 | ||
178 | into /etc/profile and inspect any shell scripts run from cron for | |
179 | constructs like [A-Z]. This will prevent things like | |
180 | ||
181 | rm [A-Z]* | |
182 | ||
183 | from removing every file in the current directory except those beginning | |
184 | with `z' and still allow individual users to change the collation order. | |
185 | Users may put the above command into their own profiles as well, of course. | |
186 | ||
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187 | 14. Bash versions up to 1.14.7 included an undocumented `-l' operator to |
188 | the `test/[' builtin. It was a unary operator that expanded to the | |
189 | length of its string argument. This let you do things like | |
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190 | |
191 | test -l $variable -lt 20 | |
192 | ||
0628567a | 193 | for example. |
28ef6c31 | 194 | |
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195 | This was included for backwards compatibility with old versions of the |
196 | Bourne shell, which did not provide an easy way to obtain the length of | |
197 | the value of a shell variable. | |
28ef6c31 | 198 | |
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199 | This operator is not part of the POSIX standard, because one can (and |
200 | should) use ${#variable} to get the length of a variable's value. | |
201 | Bash-2.x does not support it. | |
f73dda09 | 202 | |
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203 | 15. Bash no longer auto-exports the HOME, PATH, SHELL, TERM, HOSTNAME, |
204 | HOSTTYPE, MACHTYPE, or OSTYPE variables. If they appear in the initial | |
205 | environment, the export attribute will be set, but if bash provides a | |
206 | default value, they will remain local to the current shell. | |
f73dda09 | 207 | |
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208 | 16. Bash no longer initializes the FUNCNAME, GROUPS, or DIRSTACK variables |
209 | to have special behavior if they appear in the initial environment. | |
f73dda09 | 210 | |
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211 | 17. Bash no longer removes the export attribute from the SSH_CLIENT or |
212 | SSH2_CLIENT variables, and no longer attempts to discover whether or | |
213 | not it has been invoked by sshd in order to run the startup files. | |
b80f6443 | 214 | |
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215 | 18. Bash no longer requires that the body of a function be a group command; |
216 | any compound command is accepted. | |
95732b49 | 217 | |
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218 | 19. As of bash-3.0, the pattern substitution operators no longer perform |
219 | quote removal on the pattern before attempting the match. This is the | |
220 | way the pattern removal functions behave, and is more consistent. | |
95732b49 | 221 | |
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222 | 20. After bash-3.0 was released, I reimplemented tilde expansion, incorporating |
223 | it into the mainline word expansion code. This fixes the bug that caused | |
224 | the results of tilde expansion to be re-expanded. There is one | |
225 | incompatibility: a ${paramOPword} expansion within double quotes will not | |
226 | perform tilde expansion on WORD. This is consistent with the other | |
227 | expansions, and what POSIX specifies. | |
228 | ||
229 | 21. A number of variables have the integer attribute by default, so the += | |
230 | assignment operator returns expected results: RANDOM, LINENO, MAILCHECK, | |
231 | HISTCMD, OPTIND. | |
232 | ||
233 | 22. Bash-3.x is much stricter about $LINENO correctly reflecting the line | |
234 | number in a script; assignments to LINENO have little effect. | |
235 | ||
236 | 23. By default, readline binds the terminal special characters to their | |
237 | readline equivalents. As of bash-3.1/readline-5.1, this is optional and | |
238 | controlled by the bind-tty-special-chars readline variable. | |
239 | ||
240 | 24. The \W prompt string expansion abbreviates $HOME as `~'. The previous | |
241 | behavior is available with ${PWD##/*/}. | |
242 | ||
243 | 25. The arithmetic exponentiation operator is right-associative as of bash-3.1. | |
244 | ||
245 | 26. The rules concerning valid alias names are stricter, as per POSIX.2. | |
246 | ||
247 | 27. The Readline key binding functions now obey the convert-meta setting active | |
248 | when the binding takes place, as the dispatch code does when characters | |
249 | are read and processed. | |
250 | ||
251 | 28. The historical behavior of `trap' reverting signal disposition to the | |
252 | original handling in the absence of a valid first argument is implemented | |
253 | only if the first argument is a valid signal number. | |
254 | ||
255 | 29. In versions of bash after 3.1, the ${parameter//pattern/replacement} | |
256 | expansion does not interpret `%' or `#' specially. Those anchors don't | |
257 | have any real meaning when replacing every match. | |
258 | ||
259 | 30. Beginning with bash-3.1, the combination of posix mode and enabling the | |
260 | `xpg_echo' option causes echo to ignore all options, not looking for `-n' | |
261 | ||
262 | 31. Beginning with bash-3.2, bash follows the Bourne-shell-style (and POSIX- | |
263 | style) rules for parsing the contents of old-style backquoted command | |
264 | substitutions. Previous versions of bash attempted to recursively parse | |
265 | embedded quoted strings and shell constructs; bash-3.2 uses strict POSIX | |
266 | rules to find the closing backquote and simply passes the contents of the | |
267 | command substitution to a subshell for parsing and execution. | |
268 | ||
269 | 32. Beginning with bash-3.2, bash uses access(2) when executing primaries for | |
270 | the test builtin and the [[ compound command, rather than looking at the | |
271 | file permission bits obtained with stat(2). This obeys restrictions of | |
272 | the file system (e.g., read-only or noexec mounts) not available via stat. | |
273 | ||
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274 | 33. Bash-3.2 adopts the convention used by other string and pattern matching |
275 | operators for the `[[' compound command, and matches any quoted portion | |
276 | of the right-hand-side argument to the =~ operator as a string rather | |
277 | than a regular expression. | |
278 | ||
279 | 34. Bash-4.0 allows the behavior in the previous item to be modified using | |
280 | the notion of a shell `compatibility level'. | |
281 | ||
282 | 35. Bash-3.2 (patched) and Bash-4.0 fix a bug that leaves the shell in an | |
283 | inconsistent internal state following an assignment error. One of the | |
284 | changes means that compound commands or { ... } grouping commands are | |
285 | aborted under some circumstances in which they previously were not. | |
286 | This is what Posix specifies. | |
287 | ||
288 | 36. Bash-4.0 now allows process substitution constructs to pass unchanged | |
289 | through brace expansion, so any expansion of the contents will have to be | |
290 | separately specified, and each process subsitution will have to be | |
291 | separately entered. | |
292 | ||
293 | 37. Bash-4.0 now allows SIGCHLD to interrupt the wait builtin, as Posix | |
294 | specifies, so the SIGCHLD trap is no longer always invoked once per | |
295 | exiting child if you are using `wait' to wait for all children. | |
296 | ||
297 | 38. Since bash-4.0 now follows Posix rules for finding the closing delimiter | |
298 | of a $() command substitution, it will not behave as previous versions | |
299 | did, but will catch more syntax and parsing errors before spawning a | |
300 | subshell to evaluate the command substitution. | |
301 | ||
302 | 39. The programmable completion code uses the same set of delimiting characters | |
303 | as readline when breaking the command line into words, rather than the | |
304 | set of shell metacharacters, so programmable completion and readline | |
305 | should be more consistent. | |
306 | ||
307 | 40. When the read builtin times out, it attempts to assign any input read to | |
308 | specified variables, which also causes variables to be set to the empty | |
309 | string if there is not enough input. Previous versions discarded the | |
310 | characters read. | |
311 | ||
312 | 41. Beginning with bash-4.0, when one of the commands in a pipeline is killed | |
313 | by a SIGINT while executing a command list, the shell acts as if it | |
314 | received the interrupt. | |
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315 | |
316 | 42. Bash-4.0 changes the handling of the set -e option so that the shell exits | |
317 | if a pipeline fails (and not just if the last command in the failing | |
318 | pipeline is a simple command). This is not as Posix specifies. There is | |
319 | work underway to update this portion of the standard; the bash-4.0 | |
320 | behavior attempts to capture the consensus at the time of release. |