#! perl -slw
use strict;
use constant MONTHS => { qw[
    Jan 0 Feb 31 Mar 59 Apr 90 May 120 Jun 151
    Jul 181 Aug 212 Sep 242 Oct 272 Nov 303 Dec 334
] };

sub str2epoch {
    my( $d, $m, $y, $H, $M, $S ) = $_[0] =~
        m[^.... (\d\d) (...) (\d\d\d\d) (\d\d):(\d\d):(\d\d)] 
        or die "Bad format $_[0]";
        
    my $leaps =  int( ($y - 1970) / 4 + 0.5 );
    (((($y-1970)*365 +$leaps+MONTHS->{$m}+($d-1))*24 +$H)*60 +$M)*60 +$S;
}

my $date = 'Fri, 01 Mar 2013 01:21:14 +0000';;
print str2epoch( $date );

print scalar localtime str2epoch( $date );

print scalar localtime str2epoch( 'Fri, 12 Jul 2013 01:20:34' );;

__END__
C:\test\primes>..\str2epoch.pl
1362100874
Fri Mar  1 01:21:14 2013
Fri Jul 12 02:20:34 2013