http://www.perlmonks.org?node_id=1026261


in reply to Wrong idioms

sub readfile {
    my $filename = shift or return;
    ...
}

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If this code should only check that filename is defined (i.e. allow empty string), you can write (even for perl <5.10) it like this: 
defined(my $filename = shift) or return;

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In Section Seekers of Perl Wisdom