D:\>perl -we"print 1 <=> undef
Use of uninitialized value in numeric comparison (<=>) at -e line 1.
1
D:\>perl -we"print 1 + undef
Use of uninitialized value in addition (+) at -e line 1.
1
D:\>perl -we"print 1 - undef
Use of uninitialized value in subtraction (-) at -e line 1.
1
D:\>