The camel book lists the following (among others) as being equivalent: 
while (defined($_=<STDIN>)) ...
while ($_=<STDIN>) ...
while (<STDIN>) ...

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so I guess that only in the case of a while both the second and third form are equivalent to the first. This is not true for other boolean context like eg if.

In reply to Re^2: Doubt on defined-ness by waldner
in thread Doubt on defined-ness by waldner

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