You can use glob with a single directory or File::Find for a directory tree.

#! /usr/bin/perl
#

use strict;
use warnings;

use File::Find;

foreach (glob('*.txt')) {
    print "Found $_ using glob\n";
}

find(\&wanted, '.');

sub wanted {
    return unless /\S+\.txt/i;
    print "Found $_ using File::Find\n";
    
    #Do something with $_
}
[download]