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

my $file_contents;
while( <DATA> ){
  next unless ( /^--/ || /^$/ );
  $file_contents .= $_;
}
print $file_contents;

__DATA__
--keep me
delete me

-- don't not throw this one out.
-- delete every line that does NOT begin with two dashes...
-- is the same as keep every line that begins with two dashes