#!/usr/bin/env perl 
use strict;
use warnings;
use Data::Dumper;

my $initialStr = "[20150302 22:01:05] [1, 2, 3, 4] String0\n [20150302 22:01:05] [1, 2, 3, 4] String1\n [20150302 22:01:05] [1, 2, 3, 4] String2\n [20150302 22:01:05] [1, 2, 3, 4] String3\n [20150302 22:01:05] [1, 2, 3, 4] String4\n [20150302 22:01:05] [1, 2, 3, 4] String5\n [20150302 22:01:05] [1, 2, 3, 4] String6\n [20150302 22:01:05] [1, 2, 3, 4] String7\n";

my @matches = $initialStr =~ /\[\d+ \d{2}:\d{2}:\d{2}\]\s+(.+)\n/g;

print Dumper \@matches;