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Imported from ../bash-3.1.tar.gz.

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Jari Aalto 2005-12-07 14:08:12 +00:00
commit 95732b497d
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95
POSIX
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@ -1,5 +1,5 @@
Bash POSIX Mode
===============
6.11 Bash POSIX Mode
====================
Starting Bash with the `--posix' command-line option or executing `set
-o posix' while Bash is running will cause Bash to conform more closely
@ -22,58 +22,59 @@ The following list is what's changed when `POSIX mode' is in effect:
is stopped is `Stopped(SIGNAME)', where SIGNAME is, for example,
`SIGTSTP'.
4. Reserved words may not be aliased.
4. The `bg' builtin uses the required format to describe each job
placed in the background, which does not include an indication of
whether the job is the current or previous job.
5. The POSIX 1003.2 `PS1' and `PS2' expansions of `!' to the history
5. Reserved words appearing in a context where reserved words are
recognized do not undergo alias expansion.
6. The POSIX 1003.2 `PS1' and `PS2' expansions of `!' to the history
number and `!!' to `!' are enabled, and parameter expansion is
performed on the values of `PS1' and `PS2' regardless of the
setting of the `promptvars' option.
6. The POSIX 1003.2 startup files are executed (`$ENV') rather than
7. The POSIX 1003.2 startup files are executed (`$ENV') rather than
the normal Bash files.
7. Tilde expansion is only performed on assignments preceding a
8. Tilde expansion is only performed on assignments preceding a
command name, rather than on all assignment statements on the line.
8. The default history file is `~/.sh_history' (this is the default
9. The default history file is `~/.sh_history' (this is the default
value of `$HISTFILE').
9. The output of `kill -l' prints all the signal names on a single
10. The output of `kill -l' prints all the signal names on a single
line, separated by spaces, without the `SIG' prefix.
10. The `kill' builtin does not accept signal names with a `SIG'
11. The `kill' builtin does not accept signal names with a `SIG'
prefix.
11. Non-interactive shells exit if FILENAME in `.' FILENAME is not
12. Non-interactive shells exit if FILENAME in `.' FILENAME is not
found.
12. Non-interactive shells exit if a syntax error in an arithmetic
13. Non-interactive shells exit if a syntax error in an arithmetic
expansion results in an invalid expression.
13. Redirection operators do not perform filename expansion on the word
14. Redirection operators do not perform filename expansion on the word
in the redirection unless the shell is interactive.
14. Redirection operators do not perform word splitting on the word in
15. Redirection operators do not perform word splitting on the word in
the redirection.
15. Function names must be valid shell `name's. That is, they may not
16. Function names must be valid shell `name's. That is, they may not
contain characters other than letters, digits, and underscores, and
may not start with a digit. Declaring a function with an invalid
name causes a fatal syntax error in non-interactive shells.
16. POSIX 1003.2 `special' builtins are found before shell functions
17. POSIX 1003.2 special builtins are found before shell functions
during command lookup.
17. If a POSIX 1003.2 special builtin returns an error status, a
18. If a POSIX 1003.2 special builtin returns an error status, a
non-interactive shell exits. The fatal errors are those listed in
the POSIX.2 standard, and include things like passing incorrect
options, redirection errors, variable assignment errors for
assignments preceding the command name, and so on.
18. If the `cd' builtin finds a directory to change to using
`$CDPATH', the value it assigns to the `PWD' variable does not
contain any symbolic links, as if `cd -P' had been executed.
19. If `CDPATH' is set, the `cd' builtin will not implicitly append
the current directory to it. This means that `cd' will fail if no
valid directory name can be constructed from any of the entries in
@ -105,9 +106,10 @@ The following list is what's changed when `POSIX mode' is in effect:
27. The `trap' builtin doesn't check the first argument for a possible
signal specification and revert the signal handling to the original
disposition if it is. If users want to reset the handler for a
given signal to the original disposition, they should use `-' as
the first argument.
disposition if it is, unless that argument consists solely of
digits and is a valid signal number. If users want to reset the
handler for a given signal to the original disposition, they
should use `-' as the first argument.
28. The `.' and `source' builtins do not search the current directory
for the filename argument if it is not found by searching `PATH'.
@ -134,19 +136,44 @@ The following list is what's changed when `POSIX mode' is in effect:
argument does not refer to an existing directory, `cd' will fail
instead of falling back to PHYSICAL mode.
There is other POSIX 1003.2 behavior that Bash does not implement.
Specifically:
35. When the `pwd' builtin is supplied the `-P' option, it resets
`$PWD' to a pathname containing no symlinks.
1. Assignment statements affect the execution environment of all
builtins, not just special ones.
36. The `pwd' builtin verifies that the value it prints is the same as
the current directory, even if it is not asked to check the file
system with the `-P' option.
2. When a subshell is created to execute a shell script with execute
permission, but without a leading `#!', Bash sets `$0' to the full
pathname of the script as found by searching `$PATH', rather than
the command as typed by the user.
37. When listing the history, the `fc' builtin does not include an
indication of whether or not a history entry has been modified.
3. When using `.' to source a shell script found in `$PATH', bash
checks execute permission bits rather than read permission bits,
just as if it were searching for a command.
38. The default editor used by `fc' is `ed'.
39. The `type' and `command' builtins will not report a non-executable
file as having been found, though the shell will attempt to
execute such a file if it is the only so-named file found in
`$PATH'.
40. The `vi' editing mode will invoke the `vi' editor directly when
the `v' command is run, instead of checking `$FCEDIT' and
`$EDITOR'.
41. When the `xpg_echo' option is enabled, Bash does not attempt to
interpret any arguments to `echo' as options. Each argument is
displayed, after escape characters are converted.
There is other POSIX 1003.2 behavior that Bash does not implement by
default even when in POSIX mode. Specifically:
1. The `fc' builtin checks `$EDITOR' as a program to edit history
entries if `FCEDIT' is unset, rather than defaulting directly to
`ed'. `fc' uses `ed' if `EDITOR' is unset.
2. As noted above, Bash requires the `xpg_echo' option to be enabled
for the `echo' builtin to be fully conformant.
Bash can be configured to be POSIX-conformant by default, by specifying
the `--enable-strict-posix-default' to `configure' when building (*note
Optional Features::).