in reply to Explaining Perl truth to beginners

For beginners: the output of a boolean operation is reliably interpreted as true or false. Everything else should be tested by comparison.

The one idiomatic exception I can think of is 

while (<INPUT>) {
...

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which has an implicit boolean test in it. Nothing else springs to my mind.
Caution: Contents may have been coded under pressure.

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Re^2: Explaining Perl truth to beginners
by ysth (Canon) on Nov 22, 2005 at 12:51 UTC
    which has an implicit boolean test in it.
    Actually, an implicit defined() test in it: 
    $ perl -MO=Deparse -e'while (<INPUT>) {}'
while (defined($_ = <INPUT>)) {
    ();
}
-e syntax OK

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    so that e.g. a 0 with no following newline at the end of a file still goes into the body of the loop.
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[d/l]

In Section Seekers of Perl Wisdom