1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
|
Starting bash with the `--posix' command-line option or executing
`set -o posix' 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 `posix mode' is in effect:
1. When a command in the hash table no longer exists, bash will re-search
$PATH to find the new location. This is also available with
`shopt -s checkhash'.
2. The >& redirection does not redirect stdout and stderr.
3. The message printed by the job control code and builtins when a job
exits with a non-zero status is `Done(status)'.
4. Reserved words may not be aliased.
5. The Posix.2 PS1 and PS2 expansions of `!' -> history number and
`!!' -> `!' are enabled, and parameter expansion is performed on
the value regardless of the setting of the `promptvars' option.
6. Interactive comments are enabled by default. (Note that bash has
them on by default anyway.)
7. The Posix.2 startup files are executed ($ENV) rather than the normal
bash files.
8. Tilde expansion is only performed on assignments preceding a command
name, rather than on all assignment statements on the line.
9. The default history file is ~/.sh_history (default value of $HISTFILE).
10. The output of `kill -l' prints all the signal names on a single line,
separated by spaces.
11. Non-interactive shells exit if `file' in `. file' is not found.
12. Redirection operators do not perform pathname expansion on the word
in the redirection unless the shell is interactive
13. Function names must be valid shell identifiers. 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 illegal name
causes a fatal syntax error in non-interactive shells.
14. Posix.2 `special' builtins are found before shell functions during command
lookup.
15. If a Posix.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.
16. The environment passed to executed commands is not sorted. Neither is
the output of `set'. This is not strictly Posix.2 behavior, but sh
does it this way. Ksh does not. It's not necessary to sort the
environment; no program should rely on it being sorted.
17. If the `cd' builtin finds a directory to change to using $CDPATH, the
value it assigns to $PWD does not contain any symbolic links, as if
`cd -P' had been executed.
18. A non-interactive shell exits with an error status if a variable
assignment error occurs when no command name follows the assignment
statements. A variable assignment error occurs, for example, when
trying to assign a value to a read-only variable.
19. A non-interactive shell exits with an error status if the iteration
variable in a for statement or the selection variable in a select
statement is a read-only variable.
20. Process substitution is not available.
21. Assignment statements preceding POSIX.2 `special' builtins persist in
the shell environment after the builtin completes.
There is other Posix.2 behavior that bash does not implement. Specifically:
1. Assignment statements affect the execution environment of all builtins,
not just special ones.
|
