c:\@Work\Perl>perl -wMstrict -le
"print 'perl version ', $];
 ;;
 print 'undefined A: >', defined(),      '<';
 print 'undefined B: >', defined(undef), '<';
 print 'defined: >',     defined(42),    '<';
"
perl version 5.008009
undefined A: ><
undefined B: ><
defined: >1<

perl version 5.014004
undefined A: ><
undefined B: ><
defined: >1<