4 Starting Bash with the `--posix' command-line option or executing `set
5 -o posix' while Bash is running will cause Bash to conform more closely
6 to the POSIX 1003.2 standard by changing the behavior to match that
7 specified by POSIX in areas where the Bash default differs.
9 The following list is what's changed when `POSIX mode' is in effect:
11 1. When a command in the hash table no longer exists, Bash will
12 re-search `$PATH' to find the new location. This is also
13 available with `shopt -s checkhash'.
15 2. The `>&' redirection does not redirect stdout and stderr.
17 3. The message printed by the job control code and builtins when a job
18 exits with a non-zero status is `Done(status)'.
20 4. Reserved words may not be aliased.
22 5. The POSIX 1003.2 `PS1' and `PS2' expansions of `!' to the history
23 number and `!!' to `!' are enabled, and parameter expansion is
24 performed on the values of `PS1' and `PS2' regardless of the
25 setting of the `promptvars' option.
27 6. Interactive comments are enabled by default. (Bash has them on by
30 7. The POSIX 1003.2 startup files are executed (`$ENV') rather than
31 the normal Bash files.
33 8. Tilde expansion is only performed on assignments preceding a
34 command name, rather than on all assignment statements on the line.
36 9. The default history file is `~/.sh_history' (this is the default
37 value of `$HISTFILE').
39 10. The output of `kill -l' prints all the signal names on a single
40 line, separated by spaces.
42 11. Non-interactive shells exit if FILENAME in `.' FILENAME is not
45 12. Non-interactive shells exit if a syntax error in an arithmetic
46 expansion results in an invalid expression.
48 13. Redirection operators do not perform filename expansion on the word
49 in the redirection unless the shell is interactive.
51 14. Redirection operators do not perform word splitting on the word in
54 15. Function names must be valid shell `name's. That is, they may not
55 contain characters other than letters, digits, and underscores, and
56 may not start with a digit. Declaring a function with an invalid
57 name causes a fatal syntax error in non-interactive shells.
59 16. POSIX 1003.2 `special' builtins are found before shell functions
60 during command lookup.
62 17. If a POSIX 1003.2 special builtin returns an error status, a
63 non-interactive shell exits. The fatal errors are those listed in
64 the POSIX.2 standard, and include things like passing incorrect
65 options, redirection errors, variable assignment errors for
66 assignments preceding the command name, and so on.
68 18. If the `cd' builtin finds a directory to change to using
69 `$CDPATH', the value it assigns to the `PWD' variable does not
70 contain any symbolic links, as if `cd -P' had been executed.
72 19. If `$CDPATH' is set, the `cd' builtin will not implicitly append
73 the current directory to it. This means that `cd' will fail if no
74 valid directory name can be constructed from any of the entries in
75 `$CDPATH', even if the a directory with the same name as the name
76 given as an argument to `cd' exists in the current directory.
78 20. A non-interactive shell exits with an error status if a variable
79 assignment error occurs when no command name follows the assignment
80 statements. A variable assignment error occurs, for example, when
81 trying to assign a value to a readonly variable.
83 21. A non-interactive shell exits with an error status if the iteration
84 variable in a `for' statement or the selection variable in a
85 `select' statement is a readonly variable.
87 22. Process substitution is not available.
89 23. Assignment statements preceding POSIX 1003.2 special builtins
90 persist in the shell environment after the builtin completes.
92 24. The `export' and `readonly' builtin commands display their output
93 in the format required by POSIX 1003.2.
96 There is other POSIX 1003.2 behavior that Bash does not implement.
99 1. Assignment statements affect the execution environment of all
100 builtins, not just special ones.