It's possible to avoid the warning by using 1 (or 0) instead of 42. 
>perl -w -e 42
Useless use of a constant in void context at -e line 1.

>perl -w -e 1

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It's a special case to allow 1 while ...;.

In reply to Re^4: expression which does nothing by ikegami
in thread expression which does nothing by jesuashok

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