I could just as well use (and more efficient too):

if ($&) { print; }
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Ummm, no. $& is one of the "ugly three" variables (the other two are $` and $') that kill performance. From perlvar:

The use of this variable anywhere in a program imposes a considerable performance penalty on all regular expression matches. To avoid this penalty, you can extract the same substring by using @-. Starting with Perl 5.10, you can use the /p match flag and the ${^MATCH} variable to do the same thing for particular match operations.

Apart from that, it may work for this special problem, but it does not work if $& evaluates to false:

perl  -E '$x="a0b"; $x=~/0/; say $&; if ($&) { die "not reached!" } if
+ ($x=~/0/) { say "matched zero" }'
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Output:

0
matched zero
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Alexander