package AAA;
require "111.pl";
longestLineLength(@a);  # Works.
package BBB;
require "111.pl";       # Does nothing. Already required.
longestLineLength(@a);  # ERROR.

-vs-

package AAA;
do "111.pl";            # Creates &AAA::longestLineLength
longestLineLength(@a);  # Works.
package BBB;
do "111.pl";            # Creates &BBB::longestLineLength
longestLineLength(@a);  # Works.