# first num
sub num_from_str {
    my $str = shift;
    my ($num) = $str =~ /(\d+)/;
    return $num;
}
my @a = qw( ch1 ch11 ch55 ch5 ch2 ch16 );
my @sorted = sort { num_from_str($a) <=> num_from_str($b) } @a;
print "$_\n" for @sorted;
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update: ... but Sort::Key::Natural is a more complete solution, because it sorts based on the alphabetical bits as well.