sub find_hash_core {
  my $dir = './';

  opendir my $dirh, $dir or die "$dir: $!\n";
  # if you need the current workdir, see Cwd how to retrieve that and restore it later
  chdir $dir;
  my @files = grep { -f $_ } readdir $dirh;

  for ( @files ) {
    if ( m/1234yourhashvalue/ ) {
      print "found hash";
}