#! /usr/bin/perl
use strict;
use warnings;

use Getopt::Long;

### MAIN

my $call_external_program = 0;

GetOptions(
  'extern' => \$call_external_program,
) or exit 127;


if ( $call_external_program ) {
  # if option was set to execute external program, do that and terminate this script
  # provide rest of @ARGV to the external program
  exec( "external_program", @ARGV );
}

### else do some other stuff