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

sub by_the_number_at_the_end {
    $a =~ /(\d+)$/;
    my $end_of_a = $1;
    $b =~ /(\d+)$/;
    my $end_of_b = $1;
    return -1 if $end_of_a < $end_of_b;
    return 0  if $end_of_a == $end_of_b;
    return 1  if $end_of_a > $end_of_b;
}

my @array=("ch1","ch11","ch2","ch5","ch55","ch16");

print join ("\n", sort by_the_number_at_the_end @array);