#!/usr/bin/perl -w
use strict;

$_ = "[27/Feb/2002:05:05:51 -0800]";
my %months = (
	Jan => '01',
	Feb => '02',
	# ...
	Dec => '12',
);

m|\[(\d*)/(\D*)/(\d*):(\d*:\d*:\d*) [^\]]*\]|;
print "$3-$months{$2}-$1 $4";