#!/usr/bin/perl -w
use strict;

# variable to hold the previous header 
my($header);

foreach (<>) {
  if (/^Header Line (\S+)$/) {
    die "Error - header repeated in line $.\n" if ($header && $header eq $1);
    $header = $1;
    next;
  }
  if (/^[\w\*\/]{3}-[\w\*\/]{3}/) {
    # do whatever processing on the line
    print "Got a matching line...\n";
  }
}