From: PerlFAQ Server on
This is an excerpt from the latest version perlfaq6.pod, which
comes with the standard Perl distribution. These postings aim to
reduce the number of repeated questions as well as allow the community
to review and update the answers. The latest version of the complete
perlfaq is at .


6.22: What's wrong with using grep in a void context?

The problem is that grep builds a return list, regardless of the
context. This means you're making Perl go to the trouble of building a
list that you then just throw away. If the list is large, you waste both
time and space. If your intent is to iterate over the list, then use a
for loop for this purpose.

In perls older than 5.8.1, map suffers from this problem as well. But
since 5.8.1, this has been fixed, and map is context aware - in void
context, no lists are constructed.


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