-This document details the incompatibilites between this version of bash,
-bash-2.01, and the previous widely-available version, bash-1.14. These
-were discovered by alpha and beta testers, so they will likely be
-encountered by a significant number of users.
-
-1. Bash now uses a new quoting syntax, $"...", to do locale-specific
+Compatibility with previous versions
+====================================
+
+This document details the incompatibilities between this version of bash,
+bash-4.3, and the previous widely-available versions, bash-3.x (which is
+still the `standard' version for Mac OS X), 4.0/4.1 (which are still
+standard on a few Linux distributions), and bash-4.2, the current
+widely-available version. These were discovered by users of bash-2.x
+through 4.x, so this list is not comprehensive. Some of these
+incompatibilities occur between the current version and versions 2.0 and
+above.
+
+1. Bash uses a new quoting syntax, $"...", to do locale-specific
string translation. Users who have relied on the (undocumented)
behavior of bash-1.14 will have to change their scripts. For
instance, if you are doing something like this to get the value of
3. The options to `bind' have changed to make them more consistent with
the rest of the bash builtins. If you are using `bind -d' to list
- the readline keybindings in a form that can be re-read, use `bind -p'
- instead. If you were using `bind -v' to list the keybindings, use
+ the readline key bindings in a form that can be re-read, use `bind -p'
+ instead. If you were using `bind -v' to list the key bindings, use
`bind -P' instead.
4. The `long' invocation options must now be prefixed by `--' instead
"\C-\\": self-insert
-6. A number of people complained above having to use ESC to terminate an
- incremental search, and asked for an alternate mechanism. Bash-2.0
- allows ^J to terminate the search without accepting the line. Use
- ^M to terminate the search and accept the line, as in bash-1.14.
+6. A number of people complained about having to use ESC to terminate an
+ incremental search, and asked for an alternate mechanism. Bash-2.03
+ uses the value of the settable readline variable `isearch-terminators'
+ to decide which characters should terminate an incremental search. If
+ that variable has not been set, ESC and Control-J will terminate a
+ search.
7. Some variables have been removed: MAIL_WARNING, notify, history_control,
command_oriented_history, glob_dot_filenames, allow_null_glob_expansion,
An interactive shell started in posix mode reads and executes commands
from the file named by $ENV.
+
+11. The <> redirection operator was changed to conform to the POSIX.2 spec.
+ In the absence of any file descriptor specification preceding the `<>',
+ file descriptor 0 is used. In bash-1.14, this was the behavior only
+ when in POSIX mode. The bash-1.14 behavior may be obtained with
+
+ <>filename 1>&0
+
+12. The `alias' builtin now checks for invalid options and takes a `-p'
+ option to display output in POSIX mode. If you have old aliases beginning
+ with `-' or `+', you will have to add the `--' to the alias command
+ that declares them:
+
+ alias -x='chmod a-x' --> alias -- -x='chmod a-x'
+
+13. The behavior of range specificiers within bracket matching expressions
+ in the pattern matcher (e.g., [A-Z]) depends on the current locale,
+ specifically the value of the LC_COLLATE environment variable. Setting
+ this variable to C or POSIX will result in the traditional ASCII behavior
+ for range comparisons. If the locale is set to something else, e.g.,
+ en_US (specified by the LANG or LC_ALL variables), collation order is
+ locale-dependent. For example, the en_US locale sorts the upper and
+ lower case letters like this:
+
+ AaBb...Zz
+
+ so a range specification like [A-Z] will match every letter except `z'.
+ Other locales collate like
+
+ aAbBcC...zZ
+
+ which means that [A-Z] matches every letter except `a'.
+
+ The portable way to specify upper case letters is [:upper:] instead of
+ A-Z; lower case may be specified as [:lower:] instead of a-z.
+
+ Look at the manual pages for setlocale(3), strcoll(3), and, if it is
+ present, locale(1).
+
+ You can find your current locale information by running locale(1):
+
+ caleb.ins.cwru.edu(2)$ locale
+ LANG=en_US
+ LC_CTYPE="en_US"
+ LC_NUMERIC="en_US"
+ LC_TIME="en_US"
+ LC_COLLATE="en_US"
+ LC_MONETARY="en_US"
+ LC_MESSAGES="en_US"
+ LC_ALL=en_US
+
+ My advice is to put
+
+ export LC_COLLATE=C
+
+ into /etc/profile and inspect any shell scripts run from cron for
+ constructs like [A-Z]. This will prevent things like
+
+ rm [A-Z]*
+
+ from removing every file in the current directory except those beginning
+ with `z' and still allow individual users to change the collation order.
+ Users may put the above command into their own profiles as well, of course.
+
+14. Bash versions up to 1.14.7 included an undocumented `-l' operator to
+ the `test/[' builtin. It was a unary operator that expanded to the
+ length of its string argument. This let you do things like
+
+ test -l $variable -lt 20
+
+ for example.
+
+ This was included for backwards compatibility with old versions of the
+ Bourne shell, which did not provide an easy way to obtain the length of
+ the value of a shell variable.
+
+ This operator is not part of the POSIX standard, because one can (and
+ should) use ${#variable} to get the length of a variable's value.
+ Bash-2.x does not support it.
+
+15. Bash no longer auto-exports the HOME, PATH, SHELL, TERM, HOSTNAME,
+ HOSTTYPE, MACHTYPE, or OSTYPE variables. If they appear in the initial
+ environment, the export attribute will be set, but if bash provides a
+ default value, they will remain local to the current shell.
+
+16. Bash no longer initializes the FUNCNAME, GROUPS, or DIRSTACK variables
+ to have special behavior if they appear in the initial environment.
+
+17. Bash no longer removes the export attribute from the SSH_CLIENT or
+ SSH2_CLIENT variables, and no longer attempts to discover whether or
+ not it has been invoked by sshd in order to run the startup files.
+
+18. Bash no longer requires that the body of a function be a group command;
+ any compound command is accepted.
+
+19. As of bash-3.0, the pattern substitution operators no longer perform
+ quote removal on the pattern before attempting the match. This is the
+ way the pattern removal functions behave, and is more consistent.
+
+20. After bash-3.0 was released, I reimplemented tilde expansion, incorporating
+ it into the mainline word expansion code. This fixes the bug that caused
+ the results of tilde expansion to be re-expanded. There is one
+ incompatibility: a ${paramOPword} expansion within double quotes will not
+ perform tilde expansion on WORD. This is consistent with the other
+ expansions, and what POSIX specifies.
+
+21. A number of variables have the integer attribute by default, so the +=
+ assignment operator returns expected results: RANDOM, LINENO, MAILCHECK,
+ HISTCMD, OPTIND.
+
+22. Bash-3.x is much stricter about $LINENO correctly reflecting the line
+ number in a script; assignments to LINENO have little effect.
+
+23. By default, readline binds the terminal special characters to their
+ readline equivalents. As of bash-3.1/readline-5.1, this is optional and
+ controlled by the bind-tty-special-chars readline variable.
+
+24. The \W prompt string expansion abbreviates $HOME as `~'. The previous
+ behavior is available with ${PWD##/*/}.
+
+25. The arithmetic exponentiation operator is right-associative as of bash-3.1.
+
+26. The rules concerning valid alias names are stricter, as per POSIX.2.
+
+27. The Readline key binding functions now obey the convert-meta setting active
+ when the binding takes place, as the dispatch code does when characters
+ are read and processed.
+
+28. The historical behavior of `trap' reverting signal disposition to the
+ original handling in the absence of a valid first argument is implemented
+ only if the first argument is a valid signal number.
+
+29. In versions of bash after 3.1, the ${parameter//pattern/replacement}
+ expansion does not interpret `%' or `#' specially. Those anchors don't
+ have any real meaning when replacing every match.
+
+30. Beginning with bash-3.1, the combination of posix mode and enabling the
+ `xpg_echo' option causes echo to ignore all options, not looking for `-n'
+
+31. Beginning with bash-3.2, bash follows the Bourne-shell-style (and POSIX-
+ style) rules for parsing the contents of old-style backquoted command
+ substitutions. Previous versions of bash attempted to recursively parse
+ embedded quoted strings and shell constructs; bash-3.2 uses strict POSIX
+ rules to find the closing backquote and simply passes the contents of the
+ command substitution to a subshell for parsing and execution.
+
+32. Beginning with bash-3.2, bash uses access(2) when executing primaries for
+ the test builtin and the [[ compound command, rather than looking at the
+ file permission bits obtained with stat(2). This obeys restrictions of
+ the file system (e.g., read-only or noexec mounts) not available via stat.
+
+33. Bash-3.2 adopts the convention used by other string and pattern matching
+ operators for the `[[' compound command, and matches any quoted portion
+ of the right-hand-side argument to the =~ operator as a string rather
+ than a regular expression.
+
+34. Bash-4.0 allows the behavior in the previous item to be modified using
+ the notion of a shell `compatibility level'. If the compat31 shopt
+ option is set, quoting the pattern has no special effect.
+
+35. Bash-3.2 (patched) and Bash-4.0 fix a bug that leaves the shell in an
+ inconsistent internal state following an assignment error. One of the
+ changes means that compound commands or { ... } grouping commands are
+ aborted under some circumstances in which they previously were not.
+ This is what Posix specifies.
+
+36. Bash-4.0 now allows process substitution constructs to pass unchanged
+ through brace expansion, so any expansion of the contents will have to be
+ separately specified, and each process subsitution will have to be
+ separately entered.
+
+37. Bash-4.0 now allows SIGCHLD to interrupt the wait builtin, as Posix
+ specifies, so the SIGCHLD trap is no longer always invoked once per
+ exiting child if you are using `wait' to wait for all children. As
+ of bash-4.2, this is the status quo only when in posix mode.
+
+38. Since bash-4.0 now follows Posix rules for finding the closing delimiter
+ of a $() command substitution, it will not behave as previous versions
+ did, but will catch more syntax and parsing errors before spawning a
+ subshell to evaluate the command substitution.
+
+39. The programmable completion code uses the same set of delimiting characters
+ as readline when breaking the command line into words, rather than the
+ set of shell metacharacters, so programmable completion and readline
+ should be more consistent.
+
+40. When the read builtin times out, it attempts to assign any input read to
+ specified variables, which also causes variables to be set to the empty
+ string if there is not enough input. Previous versions discarded the
+ characters read.
+
+41. Beginning with bash-4.0, when one of the commands in a pipeline is killed
+ by a SIGINT while executing a command list, the shell acts as if it
+ received the interrupt. This can be disabled by setting the compat31 or
+ compat32 shell options.
+
+42. Bash-4.0 changes the handling of the set -e option so that the shell exits
+ if a pipeline fails (and not just if the last command in the failing
+ pipeline is a simple command). This is not as Posix specifies. There is
+ work underway to update this portion of the standard; the bash-4.0
+ behavior attempts to capture the consensus at the time of release.
+
+43. Bash-4.0 fixes a Posix mode bug that caused the . (source) builtin to
+ search the current directory for its filename argument, even if "." is
+ not in $PATH. Posix says that the shell shouldn't look in $PWD in this
+ case.
+
+44. Bash-4.1 uses the current locale when comparing strings using the < and
+ > operators to the `[[' command. This can be reverted to the previous
+ behavior (ASCII collating and strcmp(3)) by setting one of the
+ `compatNN' shopt options, where NN is less than 41.
+
+45. Bash-4.1 conforms to the current Posix specification for `set -u':
+ expansions of $@ and $* when there are no positional parameters do not
+ cause the shell to exit.
+
+46. Bash-4.1 implements the current Posix specification for `set -e' and
+ exits when any command fails, not just a simple command or pipeline.
+
+47. Command substitutions now remove the caller's trap strings when trap is
+ run to set a new trap in the subshell. Previous to bash-4.2, the old
+ trap strings persisted even though the actual signal handlers were reset.
+
+48. When in Posix mode, a single quote is not treated specially in a
+ double-quoted ${...} expansion, unless the expansion operator is
+ # or % or the new `//', `^', or `,' expansions. In particular, it
+ does not define a new quoting context. This is from Posix interpretation
+ 221.
+
+49. Posix mode shells no longer exit if a variable assignment error occurs
+ with an assignment preceding a command that is not a special builtin.
+
+50. Bash-4.2 attempts to preserve what the user typed when performing word
+ completion, instead of, for instance, expanding shell variable
+ references to their value.
+
+51. When in Posix mode, bash-4.2 exits if the filename supplied as an argument
+ to `.' is not found and the shell is not interactive.
+
+52. When compiled for strict Posix compatibility, bash-4.3 does not enable
+ history expansion by default in interactive shells, since it results in
+ a non-conforming environment.
+
+53. Bash-4.3 runs the replacement string in the pattern substitution word
+ expansion through quote removal. The code already treats quote
+ characters in the replacement string as special; if it treats them as
+ special, then quote removal should remove them.
+
+Shell Compatibility Level
+=========================
+
+Bash-4.0 introduced the concept of a `shell compatibility level', specified
+as a set of options to the shopt builtin (compat31, compat32, compat40,
+compat41, and compat42 at this writing). There is only one current
+compatibility level -- each option is mutually exclusive. This list does not
+mention behavior that is standard for a particular version (e.g., setting
+compat32 means that quoting the rhs of the regexp matching operator quotes
+special regexp characters in the word, which is default behavior in bash-3.2
+and above).
+
+Bash-4.3 introduces a new shell variable: BASH_COMPAT. The value assigned
+to this variable (a decimal version number like 4.2, or an integer
+corresponding to the compatNN option, like 42) determines the compatibility
+level.
+
+compat31 set
+ - the < and > operators to the [[ command do not consider the current
+ locale when comparing strings; they use ASCII ordering
+ - quoting the rhs of the regexp matching operator (=~) has no
+ special effect
+
+compat32 set
+ - the < and > operators to the [[ command do not consider the current
+ locale when comparing strings; they use ASCII ordering
+
+compat40 set
+ - the < and > operators to the [[ command do not consider the current
+ locale when comparing strings; they use ASCII ordering
+ - interrupting a command list such as "a ; b ; c" causes the execution
+ of the entire list to be aborted (in versions before bash-4.0,
+ interrupting one command in a list caused the next to be executed)
+
+compat41 set
+ - interrupting a command list such as "a ; b ; c" causes the execution
+ of the entire list to be aborted (in versions before bash-4.1,
+ interrupting one command in a list caused the next to be executed)
+ - when in posix mode, single quotes in the `word' portion of a
+ double-quoted parameter expansion define a new quoting context and
+ are treated specially
+
+compat42 set
+ - the replacement string in double-quoted pattern substitution is not
+ run through quote removal, as in previous versions
+-------------------------------------------------------------------------------
+
+Copying and distribution of this file, with or without modification,
+are permitted in any medium without royalty provided the copyright
+notice and this notice are preserved. This file is offered as-is,
+without any warranty.
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