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 `$PATH' to find the new location. This is also
13 available with `shopt -s checkhash'.
15 2. The message printed by the job control code and builtins when a job
16 exits with a non-zero status is `Done(status)'.
18 3. The message printed by the job control code and builtins when a job
19 is stopped is `Stopped(SIGNAME)', where SIGNAME is, for example,
22 4. Reserved words may not be aliased.
24 5. The POSIX 1003.2 `PS1' and `PS2' expansions of `!' to the history
25 number and `!!' to `!' are enabled, and parameter expansion is
26 performed on the values of `PS1' and `PS2' regardless of the
27 setting of the `promptvars' option.
29 6. Interactive comments are enabled by default. (Bash has them on by
32 7. The POSIX 1003.2 startup files are executed (`$ENV') rather than
33 the normal Bash files.
35 8. Tilde expansion is only performed on assignments preceding a
36 command name, rather than on all assignment statements on the line.
38 9. The default history file is `~/.sh_history' (this is the default
39 value of `$HISTFILE').
41 10. The output of `kill -l' prints all the signal names on a single
42 line, separated by spaces.
44 11. Non-interactive shells exit if FILENAME in `.' FILENAME is not
47 12. Non-interactive shells exit if a syntax error in an arithmetic
48 expansion results in an invalid expression.
50 13. Redirection operators do not perform filename expansion on the word
51 in the redirection unless the shell is interactive.
53 14. Redirection operators do not perform word splitting on the word in
56 15. Function names must be valid shell `name's. That is, they may not
57 contain characters other than letters, digits, and underscores, and
58 may not start with a digit. Declaring a function with an invalid
59 name causes a fatal syntax error in non-interactive shells.
61 16. POSIX 1003.2 `special' builtins are found before shell functions
62 during command lookup.
64 17. If a POSIX 1003.2 special builtin returns an error status, a
65 non-interactive shell exits. The fatal errors are those listed in
66 the POSIX.2 standard, and include things like passing incorrect
67 options, redirection errors, variable assignment errors for
68 assignments preceding the command name, and so on.
70 18. If the `cd' builtin finds a directory to change to using
71 `$CDPATH', the value it assigns to the `PWD' variable does not
72 contain any symbolic links, as if `cd -P' had been executed.
74 19. If `CDPATH' is set, the `cd' builtin will not implicitly append
75 the current directory to it. This means that `cd' will fail if no
76 valid directory name can be constructed from any of the entries in
77 `$CDPATH', even if the a directory with the same name as the name
78 given as an argument to `cd' exists in the current directory.
80 20. A non-interactive shell exits with an error status if a variable
81 assignment error occurs when no command name follows the assignment
82 statements. A variable assignment error occurs, for example, when
83 trying to assign a value to a readonly variable.
85 21. A non-interactive shell exits with an error status if the iteration
86 variable in a `for' statement or the selection variable in a
87 `select' statement is a readonly variable.
89 22. Process substitution is not available.
91 23. Assignment statements preceding POSIX 1003.2 special builtins
92 persist in the shell environment after the builtin completes.
94 24. Assignment statements preceding shell function calls persist in the
95 shell environment after the function returns, as if a POSIX
96 special builtin command had been executed.
98 25. The `export' and `readonly' builtin commands display their output
99 in the format required by POSIX 1003.2.
101 26. The `trap' builtin displays signal names without the leading `SIG'.
103 27. The `.' and `source' builtins do not search the current directory
104 for the filename argument if it is not found by searching `PATH'.
106 28. Subshells spawned to execute command substitutions inherit the
107 value of the `-e' option from the parent shell. When not in POSIX
108 mode, Bash clears the `-e' option in such subshells.
110 29. Alias expansion is always enabled, even in non-interactive shells.
112 30. When the `set' builtin is invoked without options, it does not
113 display shell function names and definitions.
116 There is other POSIX 1003.2 behavior that Bash does not implement.
119 1. Assignment statements affect the execution environment of all
120 builtins, not just special ones.
122 2. When a subshell is created to execute a shell script with execute
123 permission, but without a leading `#!', Bash sets `$0' to the full
124 pathname of the script as found by searching `$PATH', rather than
125 the command as typed by the user.
127 3. When using `.' to source a shell script found in `$PATH', bash
128 checks execute permission bits rather than read permission bits,
129 just as if it were searching for a command.