$a is a poor choice for a variable name there... particularly if you don't lexicalize it with my. $a is special you see. It has to do with sort and globalness...

In any case, you'd probably benifit from closing the rsh when you're done with it. Oh, dear. I just noticed Net::Rsh uses $a in it's example and doesn't mention a close method. That module may not be any good — I've never tried it, so I couldn't say, but the documentation is giving it a bad name.