2010-12-another-file.html
2010-7-this-is-an.html

##</code><code>##

2010-07-this-is-an.html
2010-12-another-file.html

##</code><code>##

$month =~ s/^(\d)$/0$1/; # adds leading zero if there is just a single
                         # digit- otherwise has no effect
                         # *** I recommend this idea for 
                         #     your application. ****

$month = sprintf("%02d", $month); # re-assigns a new string value 
                                  # to $month no matter what