Options
Options are settings that change shell and/or script
behavior. The set command
enables options within a script. At the point in the script
where you want the options to take effect, use set
-o option-name or, in short form, set
-option-abbrev. These two forms are equivalent. #!/bin/bash
set -o verbose
# Echoes all commands before executing.
|
#!/bin/bash
set -v
# Exact same effect as above.
|
| To disable an option within a script,
use set +o option-name or set
+option-abbrev. |
#!/bin/bash
set -o verbose
# Command echoing on.
command
...
command
set +o verbose
# Command echoing off.
command
# Not echoed.
set -v
# Command echoing on.
command
...
command
set +v
# Command echoing off.
command
exit 0
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An alternate method of enabling options in a script is
to specify them immediately following the
#! script header. #!/bin/bash -x
#
# Body of script follows.
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It is also possible to enable script options from the command
line. Some options that will not work with
set are available this way. Among these
are -i, force script to run
interactive. bash -v script-name bash -o verbose script-name The following is a listing of some useful options. They may be
specified in either abbreviated form or by complete name. Table 31-1. bash options | Abbreviation | Name | Effect |
|---|
| -C | noclobber | Prevent overwriting of files by redirection (may be
overridden by >|) | | -D | (none) | List double-quoted strings prefixed by $,
but do not execute commands in script | | -a | allexport | Export all defined variables | | -b | notify | Notify when jobs running in background terminate (not of
much use in a script) | | -c ... | (none) | Read commands from ... | | -f | noglob | Filename expansion (globbing) disabled | | -i | interactive | Script runs in interactive mode | | -p | privileged | Script runs as "suid" (caution!) | | -r | restricted | Script runs in restricted
mode (see Chapter 21). | | -u | nounset | Attempt to use undefined variable
outputs error message, and forces an exit | | -v | verbose | Print each command to stdout before executing it | | -x | xtrace | Similar to -v, but expands commands | | -e | errexit | Abort script at first error (when a command exits with
non-zero status) | | -n | noexec | Read commands in script, but do not execute them (syntax check) | | -s | stdin | Read commands from stdin | | -t | (none) | Exit after first command | | - | (none) | End of options flag. All other arguments
are positional
parameters. | | -- | (none) | Unset positional parameters.
If arguments given (-- arg1 arg2),
positional parameters set to arguments. |
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