But as a side note, perlsub has an example for grep :

      And here’s a reimplementation of the Perl "grep" operator:

           sub mygrep (&@) {
               my $code = shift;
               my @result;
               foreach $_ (@_) {
                   push(@result, $_) if &$code;
               }
               @result;
           }
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HTH!

There is one instance where while sets $_ (or at the very least has the appearance to do so), and that's in the special while( <$filehandle> ) {...} construction (or ... while <$filehandle> for that matter, I believe).