sub find_all_textfiles {
    my ($dir) = @_;
    my $fh = new IO::File;
    opendir($fh, $dir) or die "Failed to read dir '$dir' ($!)\n";
    my @files = readdir($fh);
    closedir $fh;

    my @found = ( );
    foreach my $fname (@files) {
        next if $fname eq '.' or $fname eq '..';
        my $path = "$dir/$fname";
        if (-f $path and $path =~ /[.]txt$/) {
            push @found, $path;
        } elsif (-d $path) {
            push @found, find_all_textfiles($path);
        }
    }

    return @found;
}