In recent version of perl (5.6.0 and above) you can suppress this warning using the lexically scoped:

no warnings "once";
[download]

The following script will complain about tigers, but not lions...

#!/usr/bin/perl -wT

{
  no warnings "once";
  $lions = 123;
}

$tigers = 456;

print "Hello world\n";
[download]

The full list of default categories can be found at perllexwarn.

-Blake