Several people have already mentioned a few ways to grab files and use the -M test for modification times -- However, you might want to consider using the File::Find module for this, as it will take care of recursively searching a given directory for you and some of the other menial labour involved. The following will give you all the files under the './misc' directory that have been modified within the last day (relative to script start time):

#!/usr/bin/perl -w
use strict;
use File::Find;
my @files;
find(sub{
        push @files, $File::Find::name if -M $_ < 1;
     },
     './misc');

print join "\n", @files;
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See the docs on File::Find for further information.