I don't so much object to the destructive grep as to the fact that it's using a substitution for what should be a negated pattern match: 
my @lines = grep { s/^\s+//; s/\s+$//; length > 0 && !/^#/ } <$in>;

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But this is all aesthetics anyway,

In reply to Re: A perverse use of grep by Errto
in thread A perverse use of grep by eyepopslikeamosquito

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