#!/usr/bin/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+:\d+/ );

print Dumper \@matches;

__END__

$VAR1 = [
          1
        ];

##</code><code>##

$VAR1 = [
          [1, 2, 3, 4] String0,
          [1, 2, 3, 4] String1,
          [1, 2, 3, 4] String2,
          [1, 2, 3, 4] String3,
          [1, 2, 3, 4] String4,
          [1, 2, 3, 4] String5,
          [1, 2, 3, 4] String6,
          [1, 2, 3, 4] String7
        ];