You’re just having precedence problems with the various operators. Change the second print statement to:

print 'a' cmp 'b', "\n"; # -1
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i.e., use the comma operator instead of the concatenation operator. And repeat for the other print statements. You should then get the results you’re expecting.

Update: To clarify: the concatenation operator . has a higher precedence than the stringwise comparison operator cmp, so your second print statement is parsed as print 'a' cmp ( 'b' . "\n" ); But the comma operator , has lower precedence, so it parses as you expect. See Operator Precedence and Associativity.

Hope that helps,