in reply to grepping
{ my %data; @data{@data} = 1; # turn @data into a lookup hash foreach ( @data2 ) { print "This $_ was not found.\n" if not exists $data{$_} } }
Update: An aside with MeowChow has convinced me that @data{@data} = undef; # turn @data into a lookup hash is less misleading. As with the "= 1" form above, only the value for the first key is set, and all remaining values are set to undef. Since we're just using the hash as a way to trade time for space in detecting the presense of keys, values don't matter. But the originally was slightly misleading nonetheless.
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Seekers of Perl Wisdom