#!/usr/bin/perl

use strict;
use warnings;

my $val = $Some::Nonexistent::Pkg::variable;

##</code><code>##

$ ./warnme.pl
Name "Some::Nonexistent::Pkg::variable" used only once: possible typo at ./warnme.pl line 6.
$ _

##</code><code>##

package WarnMe;

use strict;
use warnings;

my $val = $Some::Nonexistent::Pkg::variable;

1;

##</code><code>##

#!/usr/bin/perl

use strict;
use warnings;

use WarnMe;

# ...

##</code><code>##

$ ./warnme.pl
$ _