my ($pre, $suf) = split ("." , $DOMAIN);

The mistake here is that you used "" for split's first argument. split takes a regex as its first argument. There is one exception: the string ' ' (a single chr(32) character), which is special. Every other string you pass it is interpreted as a regex.

If you write it as it is interpreted, the mistake is easier to find:

split /./, $DOMAIN
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It is now clear even to human beings that the . is a regex. It is a metacharacter, so you need to escape it if you want it to be matched literally:

split /\./, $DOMAIN  # or split /[.]/, $DOMAIN
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