Hope fully this helps.

#!/usr/local/bin/perl
use strict;
use Date::Manip;

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

my $date = '';

if ($line =~ /\[([^\]]+)\]/) {
    $date = $1;
}

my $secs = UnixDate(ParseDate($date),"%s");
print "$secs\n";
print localtime($secs)."\n";
[download]

You can also throw the DateCalc sub in there for your time zone.

UPDATE: Better solution

$Date::Manip::TZ = '-0800';
my $line = qq{1.2.3.4 - - [15/May/2003:01:05:02 -0600] "GET /foobar"};

my $date = '';

if ($line =~ /\[([^\]]+)\]/) {
    $date = $1;
}
my $tz = (split(/\s+/,$date))[1];

print "$date $tz\n";
my $secs = UnixDate(Date_ConvTZ(ParseDate($date),$tz,'GMT' ),"%s");
print "$secs\n";
print localtime($secs)."\n";
[download]

grep

Mynd you, mønk bites Kan be pretti nasti...