The condition will be false if $_ is undef or 0 or the empty string (or whatever else perl deems to evaluate to false.)

So, if your last line is not terminated by a newline and is the string "0", you'll get tripped on this if don't for defined-ness.

Update: Considering the discussion below, I should have made it clear that this is a potential problem only for if statements (which is what the OP asked about), not while statements.

What is interesting is that even though the condition expression for while and if statements is executed in "boolean" context, the magic of the diamond operator only happens in while statements. 

use strict;
use warnings;
use Contextual::Return;
use Carp;

while (foo()) { last; }
while (my $x = foo()) { last; }
if (foo()) { }
if (my $z = foo()) { }

sub foo {
  return
    BOOL          { carp "BOOL"; 1; }
    SCALAR        { carp "SCALAR"; 1; }
  ;
}
__END__
BOOL at ./cr line 6
BOOL at ./cr line 7
BOOL at ./cr line 8
BOOL at ./cr line 9

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In reply to Re: Doubt on defined-ness by pc88mxer
in thread Doubt on defined-ness by waldner

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