Well, lets assume the original programmer was considerate and used meaningful variable names. If the things with the "$parm" are of this style:

  if ( $parm{something} eq 'a value' ) {
      #do something
  }
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Then the $parm is really a hash (see page 50 onwards in your Camel). You may find that a number of different values being passed to the program are grouped in the %parm hash (note the name now starting with a percent sign). So somewhere at the start of the program could be a routine to read the command line parameters, and set the key / value pairs of a hash.

Another good Perl book is the "Perl Cookbook" (also called the Ram book because of the funky big horn sheep on the cover). Jam packed full of real life examples - this shows you how you actually use all those cool things written about in the Camel.