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