sub changelinks {
 my ($file) = @_;
 if (-d $file) {
  opendir(DIR, $file) || die "$!";
  my @filenames = readdir(DIR);
  foreach my $filename (@filenames) {
   if (($filename ne "." && $filename ne "..")) {
    changelinks($file."/".$filename);
   }
  }
  closedir(DIR);
 } else {
  if ($file =~ /.shtml/i) {

   And then whatever method of opening and editing each file goes here

  }
 }
}