#!/usr/bin/env perl 
# delta.pl
use strict;
use warnings                                                                           

use Time::Local; 

print getGMDelta() . qq(\n);

sub getGMDelta
{
    ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =
        localtime(time);
    $ltime = timelocal($sec,$min,$hour,$mday,$mon,$year);
    $gtime = timegm($sec,$min,$hour,$mday,$mon,$year);
    $rv = $gtime - $ltime;
    return($rv);
}

__END__

Karls-Mac-mini:monks karl$ export TZ=UTC
Karls-Mac-mini:monks karl$ ./delta.pl
0
Karls-Mac-mini:monks karl$ unset TZ
Karls-Mac-mini:monks karl$ ./delta.pl
7200