#!/usr/local/bin/perl

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

my @argv;
my $dir = $ARGV[0];

find(\&recursiveDir, $dir);

sub recursiveDir{
        my @directories = glob "*";
        if (-d)
        {
                opendir(DIR, $dir);
                while(readdir DIR)
                {
                        my @files = glob "${dir}/*pl";
                        foreach (@files) {
                        next if -d;
                        (my $txt = $_) =~ s/pl$/txt/;
                        rename($_, $txt);
                        closedir (DIR);
                        }
                }
        }
}