Chapter 30. 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
      

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.
      

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 (preceded by a single dash) or by complete name (preceded by a double dash or by -o).