#!/usr/bin/perl

# https://perlmonks.org/?node_id=1217751

use strict;
use warnings;

my $string = "firstname1:::surname1:::middlename1:::firstname2:::surname2:::middlename2:::firstname3:::surname3:::middlename3";

my @arr = $string =~ /\w+:::\w+:::\w+/g;

use Data::Dumper;
print Dumper \@arr;