perl -we 'my $foo; $fooo = 42'
Name "main::fooo" used only once: possible typo at -e line 1.

##</code><code>##

perl -we 'my $fooo; $foo = 42'
Name "main::foo" used only once: possible typo at -e line 1.

##</code><code>##

perl -we 'my $fooo;'