The command line arguments for your script live in the array @ARGV:

#!/usr/bin/perl -w

if (!@ARGV)
{
    print STDERR << "SYNTAX";
myprogram [option][filename]
            -x does something
            -y does something else
SYNTAX
    exit 1;
}
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Also, take a look at the Getopt::Std module to handle your switch processing.

-Matt