Actions tell optparse what to do when it encounters an option on the
command line. There is a fixed set of actions hard-coded into optparse;
adding new actions is an advanced topic covered in section 14.3.5, Extending optparse.
Most actions tell optparse to store a value in some variable--for
example, take a string from the command line and store it in an
If you don't specify an option action, optparse defaults to
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