[paul@paul-laptop nqp]$ perl -we '$x = 1'
Name "main::x" used only once: possible typo at -e line 1.

##</code><code>##

my $value = $SOME_PKG::SOME_VAL
   || $SOME_PKG::SOME_VAL; # warn clean

##</code><code>##

use warnings qw(single_use_vars);