$ perl -wle 'my $i; print $i'
Use of uninitialized value in print at -e line 1.
$ perl -wle 'my $i; $i += $i'
Use of uninitialized value in addition (+) at -e line 1.
$ perl -wle 'my $i; if ($i>0) {}'
Use of uninitialized value in numeric gt (>) at -e line 1.