I'm also not quite sure what you're going for here. If you have a word such as 'foo.bar', you'd probably just want to do something like

my($before, $after) = split(/\./, $word);
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Or, if the word might contain multiple periods

my @tokens = split(/\./, $word);
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If you need to check that there is a period in the word, you should use the if statement posted above before splitting. If you want to verify that a word contains only letters, you'd want to do a matching regular expression prior to the split

$word =~ /^[a-zA-Z]+\.[a-zA-Z]*$/;
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And potentially throw in some /s* if you want to check for whitespace in it.