Mea culpa for being obscure. By "left as an exercise" I meant that like_arg() was a piece that you would need to supply yourself.

The idea is to form the wildcard string at runtime. It will look something like the following (from memory):

  sub like_arg {
      my ($prewild, $string, $postwild) = @_;
      return "%" if $string eq "";
      return "%" . $string . "%" if $prewild and $postwild;
      return "%" . $string if $prewild;
      return $string . "%" if $postwild;
      "";
  }
[download]