in reply to Warning messages about useless constants ignore '0's and '1's

From perldiags (5.8.1):

Useless use of %s in void context

...

This warning will not be issued for numerical con- stants equal to 0 or 1 since they are often used in statements like

1 while sub_with_side_effects() ;
String constants that would normally evaluate to 0 or 1 are warned about.