I suggested a $File::Find::prune approach in the chatterbox, but now I wonder whether readdir() together with -f wouldn't be better (untested):

  opendir DIR, "/";
  my @files = readdir DIR;
  closedir DIR;
 
  @files = grep { -d "/$_" } @files;

  my $dirname;
  foreach $dirname @DIR {
    if (-f "/$dirname/foo.bar") {
      print "$dirname has foo.bar\n"
    };
  };
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