AltBlue wanted to test a given string to see if was syntactically valid as a domain name. Here's the code that was too long to type into the chatterbox.
sub could_be_a_host {
  my @a = split /\./, shift, -1;
  @a > 0 and
    not grep !/^[a-z0-9\-]+$/i, @a and
    not grep /^\d+$/, @a and
    not grep /^-|-$/, @a;
}

[download]
or, a slightly faster version: 
sub could_be_a_host {
  my @a = split /\./, shift, -1;
  return 0 unless @a;
  for (@a) {
    return 0 unless /^[a-z0-9\-]+$/i;
    return 0 if /^\d+$/;
    return 0 if /^-/;
    return 0 if /-$/;
  }
  1;
}

[download]
(Modified slightly per tye's suggestion, thanks!)

In reply to Test the syntactic validity of a domain name by merlyn

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