C:\>perl -we"{my $pop;}"

C:\>perl -we"{my $pop;$pop;}"
seless use of private variable in void context at -e line 1.

C:\>perl -Mdiagnostics -we"{my $pop;$pop;}"
Useless use of private variable in void context at -e line 1 (#1)
   (W void) You did something without a side effect in a context that 
+does
   nothing with the return value, such as a statement that doesn't ret
+urn a
   value from a block, or the left side of a scalar comma operator.  V
+ery
   often this points not to stupidity on your part, but a failure of P
+erl
   to parse your program the way you thought it would.  For example, y
+ou'd
   get this if you mixed up your C precedence with Python precedence a
+nd
   said

       $one, $two = 1, 2;

   when you meant to say

       ($one, $two) = (1, 2);

   Another common error is to use ordinary parentheses to construct a 
+list
   reference when you should be using square or curly brackets, for
   example, if you say

       $array = (1,2);

   when you should have said

       $array = [1,2];

   The square brackets explicitly turn a list value into a scalar valu
+e,
   while parentheses do not.  So when a parenthesized list is evaluate
+d in
   a scalar context, the comma is treated like C's comma operator, whi
+ch
   throws away the left argument, which is not what you want.  See
   perlref for more on this.

   This warning will not be issued for numerical constants 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.


C:\>
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