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"be consistent"
 
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Current Perl documentation can be found at perldoc.perl.org.

Here is our local, out-dated (pre-5.6) version:

Both grep and map build a return list, regardless of their context. This means you're making Perl go to the trouble of building up a return list that you then just ignore. That's no way to treat a programming language, you insensitive scoundrel!