extract-dkim-header.pl

#!/usr/bin/perl
#
# Parse some file or text, looking for what would appear to be a valid
# RFC-821 style email header.  Attempt to pull out the DKIM-Signature
# portion of that file and print it.
#
# Author:	pete (at) killallhumans (dot) ca

use strict;

my $text = do { local $/; <>; };

$text =~ s/\r//g;
my $dkim = undef;

if ( $text =~ /(DKIM-Signature:.*?)(?=^\s*$)/gsm ){
	$dkim = $1;
}
elsif ( $text =~ /(DKIM-Signature:.*?)(?=^\S)/gsm ){
	$dkim = $1;
}
else {
	$dkim = $1 if ( $text =~ /(DKIM-Signature:.*)/gsm );
}

die( "Could not parse DKIM-Signature\n" ) 
	unless $dkim;

print $dkim;