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

my @list = qw( C1 C12 R5 C3 C21 C2 C12 );

my @sort =
    map { $_->[0] }
    sort { $a->[1] cmp $b->[1] || $a->[2] <=> $b->[2] }
    map { [ $_, m/^(\D+)(\d+)/ ] }
    @list;


print "@sort\n";