Starting bash with the `-posix' command-line option or setting the variable
POSIXLY_CORRECT while bash is running will cause bash to conform more
closely to the Posix.2 standard by changing the behavior to match that
specified by Posix.2 in areas where the bash default differs.

The following list is what's changed when `posixly_correct' is enabled:

1.  When a command in the hash table no longer exists, bash will re-search
    $PATH to find the new location.

2.  The >& redirection does not redirect stdout and stderr.

3.  The message printed by the job control code and builtins when a job
    exits with a non-zero status is `Done(status)'.

4.  The <> redirection does not open a file for both stdin and stdout, but
    rather opens it for read-write on fd 0.

5.  Reserved words may not be aliased.

6.  The Posix.2 PS1 and PS2 expansions of `!' -> history number and `!!' -> `!'
    are enabled.

7.  Interactive comments are enabled by default.  (Note that this version has
    them on by default anyway.)

8.  The Posix.2 startup files are executed ($ENV) rather than the normal bash
    files.

9.  The first word after `command' in `bash -c command' becomes $0 and the
    rest of the arguments become $1..$n.

10. Tilde expansion is only performed on assignments preceding a command name,
    rather than on all assignment statements on the line.

11. The default history file is ~/.sh_history (default value of $HISTFILE).

12. The output of `kill -l' prints all the signal names on a single line,
    separated by spaces.

13. Non-interactive shells exit if `file' in `. file' is not found.

There is other Posix.2 behavior that bash does not implement.  Specifically:

1.  There are no `special builtins' and `regular builtins'.  All builtins
    are equivalent.  This means that:

	o assignment statements affect the execution environment of all
	  builtins, not just special ones
	o temporary assignments do not persist after Posix.2 special
	  builtins complete
	o Functions are found before Posix.2 special builtins
	o The shell does not exit upon errors while executing Posix.2
	  special builtins

2.  $LINENO does not represent the line number of a command within a function

3.  The arithmetic evaluator does not implement the `e ? e1 : e2' conditional
    expression