This... uh... doesn't meet your first criteria for good software. (And it didn't even before he updated his spec.)

Set @b = qw( a foobar c ) to see it fail.

You might get away with something like that by including some "\0"s in your join but I certainly would not recommend it. Even before he added the additional constraint that there could be no missing elements, this would be easily solved with a single loop.

-sauoq
"My two cents aren't worth a dime.";