• Use the Unix command find to find files accessed recently (-anewer):

  touch -t 200205010000 /tmp/x
  find /usr/lib/perl5/lib -anewer /tmp/x
  rm /tmp/x
  [download]

• Use Find::File and Perl's stat function:

  #!/usr/bin/perl
  use strict;
  use warnings;
  use File::Find;
  
  find ( sub {
               print $Find::File::name, "\n"
                  if (stat($Find::File::name))[8] > time - 60*60*24*30
             }
        )
  [download]

update: added find example
update2: added File::Find example