#!/usr/local/bin/perl -w
use strict;
use File::Find;

my $bench_file = 'bench.txt';

my @new_files;
find( { follow => 1,  no_chdir => 1,
        wanted => \&callback }, '/');

sub callback {
  if (! /\.$/) {            # ignore unwanted . or ..
    if ( ! `grep '$_' $bench_file` ) {
      push @new_files, $_;  # remember this file
    }
  }
}

# append unseen filenames to bench.txt file
open BENCH, ">>bench.txt"
     or die "Can not append to bench.txt";
print BENCH "$_\n" foreach (@new_files);
close BENCH;