#! /usr/bin/perl
use warnings;
use strict;

my @input = (1, 2, 3, 5, 6, 8, 10);

my @ranges = ($input[0]);
for my $i (1 .. $#input) {
    warn "\t@ranges";
    if ($input[ $i - 1 ] + 1 == $input[$i]) {
        $ranges[-1] = (split /:/, $ranges[-1])[0] . ":$input[$i]";
    } else {
        push @ranges, $input[$i];
    }
}

use Test::More tests => 1;
is_deeply \@ranges, [ '1:3', '5:6', '8', '10' ];