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Chet Ramey
83 lines
3.5 KiB
Plaintext
83 lines
3.5 KiB
Plaintext
Starting bash with the `--posix' command-line option or executing
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`set -o posix' while bash is running will cause bash to conform more
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closely to the Posix.2 standard by changing the behavior to match that
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specified by Posix.2 in areas where the bash default differs.
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The following list is what's changed when `posix mode' is in effect:
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1. When a command in the hash table no longer exists, bash will re-search
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$PATH to find the new location. This is also available with
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`shopt -s checkhash'.
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2. The >& redirection does not redirect stdout and stderr.
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3. The message printed by the job control code and builtins when a job
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exits with a non-zero status is `Done(status)'.
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4. Reserved words may not be aliased.
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5. The Posix.2 PS1 and PS2 expansions of `!' -> history number and
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`!!' -> `!' are enabled, and parameter expansion is performed on
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the value regardless of the setting of the `promptvars' option.
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6. Interactive comments are enabled by default. (Note that bash has
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them on by default anyway.)
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7. The Posix.2 startup files are executed ($ENV) rather than the normal
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bash files.
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8. Tilde expansion is only performed on assignments preceding a command
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name, rather than on all assignment statements on the line.
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9. The default history file is ~/.sh_history (default value of $HISTFILE).
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10. The output of `kill -l' prints all the signal names on a single line,
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separated by spaces.
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11. Non-interactive shells exit if `file' in `. file' is not found.
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12. Redirection operators do not perform pathname expansion on the word
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in the redirection unless the shell is interactive
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13. Function names must be valid shell identifiers. That is, they may not
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contain characters other than letters, digits, and underscores, and
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may not start with a digit. Declaring a function with an illegal name
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causes a fatal syntax error in non-interactive shells.
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14. Posix.2 `special' builtins are found before shell functions during command
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lookup.
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15. If a Posix.2 special builtin returns an error status, a non-interactive
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shell exits. The fatal errors are those listed in the POSIX.2 standard,
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and include things like passing incorrect options, redirection errors,
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variable assignment errors for assignments preceding the command name,
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and so on.
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16. The environment passed to executed commands is not sorted. Neither is
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the output of `set'. This is not strictly Posix.2 behavior, but sh
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does it this way. Ksh does not. It's not necessary to sort the
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environment; no program should rely on it being sorted.
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17. If the `cd' builtin finds a directory to change to using $CDPATH, the
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value it assigns to $PWD does not contain any symbolic links, as if
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`cd -P' had been executed.
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18. A non-interactive shell exits with an error status if a variable
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assignment error occurs when no command name follows the assignment
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statements. A variable assignment error occurs, for example, when
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trying to assign a value to a read-only variable.
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19. A non-interactive shell exits with an error status if the iteration
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variable in a for statement or the selection variable in a select
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statement is a read-only variable.
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20. Process substitution is not available.
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21. Assignment statements preceding POSIX.2 `special' builtins persist in
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the shell environment after the builtin completes.
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There is other Posix.2 behavior that bash does not implement. Specifically:
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1. Assignment statements affect the execution environment of all builtins,
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not just special ones.
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