This document details the incompatibilities between this version of bash,
bash-3.2, and the previous widely-available versions, bash-1.14 (which is
still the `standard' version for a few Linux distributions) and bash-2.x.
These were discovered by users of bash-2.x and 3.x, so this list is not
comprehensive. Some of these incompatibilities occur between the current
version and versions 2.0 and above. (The differences between bash-1.14 and
bash-2.0 were significant.)
1. Bash uses a new quoting syntax, $"...", to do locale-specific
string translation. Users who have relied on the (undocumented)
behavior of bash-1.14 will have to change their scripts. For
instance, if you are doing something like this to get the value of
a variable whose name is the value of a second variable:
eval var2=$"$var1"
you will have to change to a different syntax.
This capability is directly supported by bash-2.0:
var2=${!var1}
This alternate syntax will work portably between bash-1.14 and bash-2.0:
eval var2=\$${var1}
2. One of the bugs fixed in the YACC grammar tightens up the rules
concerning group commands ( {...} ). The `list' that composes the
body of the group command must be terminated by a newline or
semicolon. That's because the braces are reserved words, and are
recognized as such only when a reserved word is legal. This means
that while bash-1.14 accepted shell function definitions like this:
foo() { : }
bash-2.0 requires this:
foo() { :; }
This is also an issue for commands like this:
mkdir dir || { echo 'could not mkdir' ; exit 1; }
The syntax required by bash-2.0 is also accepted by bash-1.14.
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 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
of `-'. (The old form is still accepted, for the time being.)
5. There was a bug in the version of readline distributed with bash-1.14
that caused it to write badly-formatted key bindings when using
`bind -d'. The only key sequences that were affected are C-\ (which
should appear as \C-\\ in a key binding) and C-" (which should appear
as \C-\"). If these key sequences appear in your inputrc, as, for
example,
"\C-\": self-insert
they will need to be changed to something like the following:
"\C-\\": self-insert
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,
nolinks, hostname_completion_file, noclobber, no_exit_on_failed_exec, and
cdable_vars. Most of them are now implemented with the new `shopt'
builtin; others were already implemented by `set'. Here is a list of
correspondences:
MAIL_WARNING shopt mailwarn
notify set -o notify
history_control HISTCONTROL
command_oriented_history shopt cmdhist
glob_dot_filenames shopt dotglob
allow_null_glob_expansion shopt nullglob
nolinks set -o physical
hostname_completion_file HOSTFILE
noclobber set -o noclobber
no_exit_on_failed_exec shopt execfail
cdable_vars shopt cdable_vars
8. `ulimit' now sets both hard and soft limits and reports the soft limit
by default (when neither -H nor -S is specified). This is compatible
with versions of sh and ksh that implement `ulimit'. The bash-1.14
behavior of, for example,
ulimit -c 0
can be obtained with
ulimit -S -c 0
It may be useful to define an alias:
alias ulimit="ulimit -S"
9. Bash-2.01 uses a new quoting syntax, $'...' to do ANSI-C string
translation. Backslash-escaped characters in ... are expanded and
replaced as specified by the ANSI C standard.
10. The sourcing of startup files has changed somewhat. This is explained
more completely in the INVOCATION section of the manual page.
A non-interactive shell not named `sh' and not in posix mode reads
and executes commands from the file named by $BASH_ENV. A
non-interactive shell started by `su' and not in posix mode will read
startup files. No other non-interactive shells read any startup files.
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. Beginning with bash-3.1/readline-5.1, the readline key binding code obeys
the current setting of the `convert-meta' variable.