Truthiness is also discussed in Truth and Falsehood in perlsyn. As has been pointed out by others, you were testing "0\n" in the while-loop conditional and not the truly false string "0".

Update: At last, I see the point first made by LanX here: even if  <STDIN> managed to return a plain, nominally false  "0" character, the loop would still execute because  "0" is defined and the special-case while-loop is conditional upon defined-ness! Thanks to BillKSmith (here) and LanX (here) for helping the scales to fall from my eyes.

Give a man a fish:  <%-{-{-{-<

In reply to Re: truth in while condition (updated) by AnomalousMonk
in thread truth in while condition by TISON

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