use File::Find;

$source = '/somedir';
$somefile = 'somefile.txt';

traverse();

sub traverse {
    my %opts = (  wanted       =>    \&eval_files,
    );

    finddepth(\%opts, $source);
}

sub eval_files {
      if (-f && $_ eq $somefile) {
          print 'Got ', $_,"\n";
      }
}
[download]

For each item within a directory, File::Find will invoke the sub &eval_files. eval_files() does blissfully throw away items that aren't files and will shriek if the the file matches the given filename. $_ contains magically the name of the current item (dir / file).