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1 | Bash POSIX Mode |
2 | =============== | |
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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.2 standard by changing the behavior to match that | |
7 | specified by POSIX.2 in areas where the Bash default differs. | |
726f6388 | 8 | |
ccc6cda3 | 9 | The following list is what's changed when `POSIX mode' is in effect: |
726f6388 | 10 | |
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11 | 1. When a command in the hash table no longer exists, Bash will |
12 | re-search `$PATH' to find the new location. This is also | |
13 | available with `shopt -s checkhash'. | |
726f6388 | 14 | |
ccc6cda3 | 15 | 2. The `>&' redirection does not redirect stdout and stderr. |
726f6388 | 16 | |
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17 | 3. The message printed by the job control code and builtins when a job |
18 | exits with a non-zero status is `Done(status)'. | |
726f6388 | 19 | |
ccc6cda3 | 20 | 4. Reserved words may not be aliased. |
726f6388 | 21 | |
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22 | 5. The POSIX.2 `PS1' and `PS2' expansions of `!' to the history |
23 | number and `!!' to `!' are enabled, and parameter expansion is | |
24 | performed on the value regardless of the setting of the | |
25 | `promptvars' option. | |
726f6388 | 26 | |
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27 | 6. Interactive comments are enabled by default. (Note that Bash has |
28 | them on by default anyway.) | |
726f6388 | 29 | |
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30 | 7. The POSIX.2 startup files are executed (`$ENV') rather than the |
31 | normal Bash files. | |
726f6388 | 32 | |
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33 | 8. Tilde expansion is only performed on assignments preceding a |
34 | command name, rather than on all assignment statements on the line. | |
726f6388 | 35 | |
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36 | 9. The default history file is `~/.sh_history' (this is the default |
37 | value of `$HISTFILE'). | |
726f6388 | 38 | |
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39 | 10. The output of `kill -l' prints all the signal names on a single |
40 | line, separated by spaces. | |
726f6388 | 41 | |
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42 | 11. Non-interactive shells exit if FILENAME in `.' FILENAME is not |
43 | found. | |
726f6388 | 44 | |
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45 | 12. Redirection operators do not perform filename expansion on the word |
46 | in the redirection unless the shell is interactive. | |
726f6388 | 47 | |
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48 | 13. Function names must be valid shell `name's. That is, they may not |
49 | contain characters other than letters, digits, and underscores, and | |
50 | may not start with a digit. Declaring a function with an illegal | |
51 | name causes a fatal syntax error in non-interactive shells. | |
726f6388 | 52 | |
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53 | 14. POSIX.2 `special' builtins are found before shell functions during |
54 | command lookup. | |
726f6388 | 55 | |
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56 | 15. If a POSIX.2 special builtin returns an error status, a |
57 | non-interactive shell exits. The fatal errors are those listed in | |
58 | the POSIX.2 standard, and include things like passing incorrect | |
59 | options, redirection errors, variable assignment errors for | |
60 | assignments preceding the command name, and so on. | |
726f6388 | 61 | |
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62 | 16. If the `cd' builtin finds a directory to change to using |
63 | `$CDPATH', the value it assigns to the `PWD' variable does not | |
64 | contain any symbolic links, as if `cd -P' had been executed. | |
726f6388 | 65 | |
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66 | 17. A non-interactive shell exits with an error status if a variable |
67 | assignment error occurs when no command name follows the assignment | |
68 | statements. A variable assignment error occurs, for example, when | |
69 | trying to assign a value to a read-only variable. | |
70 | ||
71 | 18. A non-interactive shell exits with an error status if the iteration | |
72 | variable in a `for' statement or the selection variable in a | |
73 | `select' statement is a read-only variable. | |
74 | ||
75 | 19. Process substitution is not available. | |
76 | ||
77 | 20. Assignment statements preceding POSIX.2 `special' builtins persist | |
78 | in the shell environment after the builtin completes. | |
79 | ||
80 | ||
81 | There is other POSIX.2 behavior that Bash does not implement. | |
82 | Specifically: | |
83 | ||
84 | 1. Assignment statements affect the execution environment of all | |
85 | builtins, not just special ones. | |
726f6388 | 86 |