# foo.pl
use strict;
use warnings;

require 'bar.pl';

frobozz( 2 );

__END__


# bar.pl
use strict;
use warnings;

{
  my $x;    # same thing with "my $x = 'whatever';"

  frobozz( 1 ) unless caller;

  sub frobozz {
    ( $x ) = @_;
    print 'NOT ' unless defined eval( '$x' );
    print "OK\n";
    quux();
  }

  sub quux {
#    $x = $x;
    print 'NOT ' unless defined eval( '$x' );
    print "OK\n";
  }
}

1;

__END__