use strict;
use Date::Manip;

my $line = qq{1.2.3.4 - - [15/May/2003:01:05:02 -0600] "GET /foobar"};

my( @mon ) = ( "Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep" , "Oct", "Nov", "Dec" );
my $i = 0;
my %mon = map { $_ => ++$i } @mon;

if ($aline =~ m/
		([\d\.]+)   # IP		
		.*?\[([^\s]+?)\s  # date		
		 ([-+]\d+)  # zone
		 \]\s
		 (.*)       # text
		 /x) 
 {

	my ($ip, $date, $zone, $text) = ($1, $2, $3, $4);	
	print "($ip, $date, $zone, $text)\n";
	my ($d, $mon, $timestr) = split("/", $date);
	$d =~ s/^0//g; 
	my ($y, $h, $mn, $s) = split(":", $timestr);

	# calculate zone offset (in seconds)
	my $zf = ($zone =~ m/^-/) ? -1 : 1; # zone factor
	my @z = split("",$zone); shift @z; 
	my $zsec = $z[0]*216000+$z[1]*3600+$z[2]*60+$z[3];

	print "Log date values: $mon{$mon}, $d, $y, $h, $mn, $s\n";
	print "*** ERROR ***>> Date_SecsSince1970($mon{$mon}, $d, $y, $h, $mn, $s) = " . 
		localtime(Date_SecsSince1970($mon{$mon}, $d, $y, $h, $mn, $s)) . " <<***\n";

	my $time = Date_SecsSince1970($mon{$mon}, $d, $y, $h, $mn, $s) + $zf*$zsec;
    print "parsed time: ".localtime($time)."; original: $date $zone\n";
}

##</code><code>##

(1.2.3.4, 15/May/2003:01:05:02, -0600, "GET /foobar")
Log date values: 5, 15, 2003, 01, 05, 02
*** ERROR ***>> Date_SecsSince1970(5, 15, 2003, 01, 05, 02) = Wed May 14 18:05:02 2003 <<***
parsed time: Wed May 14 12:05:02 2003; original: 15/May/2003:01:05:02 -0600