source: vendor/bash/3.1/COMPAT

This document details the incompatibilites between this version of bash,
bash-3.1, and a previous widely-available version, bash-1.14 (which
is still the `standard' version for a few Linux distributions).  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.

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.