#!/usr/bin/perl -l

use strict;
use warnings;
use File::Find::Rule;

my $dir = '/tmp';
my @subdirs = File::Find::Rule->in($dir);

my $rule = File::Find::Rule->new;
$rule->file;
$rule->name('*.txt');

my @files = $rule->in(@subdirs);
foreach my $file(@files) {
    print $file;
}