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The Basics
Id: 84734
Status: new
Priority: 0/
Queue: Perl-Critic

Owner: Nobody in particular
Requestors: EDAVIS [...]

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Subject: Suggested policy: while (<$fh>) inside subroutine
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The following subroutine looks harmless enough: sub count_lines { my $filename = shift; open my $fh, '<', $filename or die; my $count = 0; while (<$fh>) { ++$count; } return $count; } However it is not safe to use in general because it will trample on the caller's $_. This is an easy mistake to make, because the more common foreach (...) is safe and won't affect the caller's $_. The somewhat less common while (<$fh>) construct looks like it works similarly to foreach (...) but has this hidden side effect. Perlcritic should warn about use of while (<$fh>) in a subroutine unless $_ has been explicitly localized first.

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