You'll stop iterating prematurely if you have a file named 0 (zero).
That hasn't been true for a very long time: 
perl -MO=Deparse -e 'while ($f = readdir $h) {1;}'
while (defined($f = readdir $h)) {
    '???';
}
-e syntax OK

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In reply to Re^4: readdir missing one file by JavaFan
in thread readdir missing one file by true

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