for (my $i=0; $i < 5; $i++){
    opendir(DIR,$i) or die();
    foreach my $file (readdir(DIR)) {
        # if the filename ends in "test.txt"...
        # adjust the regex as needed
        if ($file =~ /test\.txt$/) {
            print "$i, -${file}-\n";
        }
    }
    closedir(DIR);
}