There are a great number of ways to do that.
Perhaps the most common would be by passing the values during the execution of the script (at the command line in *nix).

./script.pl foo bar baz
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Now the values 'foo','bar', and 'baz' are available in @ARGV within script.pl as $ARGV[0], $ARGV[1], and $ARGV[2] repectively.

If you haven't already, a good trip to the Library or a copy of "Programming Perl" (ORA - the camel) might come in really handy. =)