Documented in For Loops in perlsyn:
As a special case, if the test in the for loop (or the corresponding while loop) is empty, it is treated as true. That is, both 
        for (;;) {
            ...
        }

[download]
and 
        while () {
            ...
        }

[download]
are treated as infinite loops.
Not very well placed documentation, and counter-intuitive from my perspective, but documented.

Update:: A little Googling pulled up while () vs. while (1), particularly Re: while () vs. while (1).

#11929 First ask yourself `How would I do this without a computer?' Then have the computer do it the same way.

In reply to Re: Why is the null while-loop condition expression true? by kennethk
in thread Why is the null while-loop condition expression true? by AnomalousMonk

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