#!/usr/bin/perl -w

use strict ;
use warnings;

for my $d qw(2005-12 2005-100 2005-1- 2005-12- 2005-123- 2005-1000) {
    printf "%-10s: ", $d;
    if ( $d =~ /\d{4}-\d{1,3}([^-\d]|$)/ ) {
      print "yep\n" ;
    } else {
      print "nope\n";
    }
}

##</code><code>##

2005-12   : yep
2005-100  : yep
2005-1-   : nope
2005-12-  : nope
2005-123- : nope
2005-1000 : nope