What do you mean with "prints nothing"? What are you trying to print? Note that you are trying to eval the string sub which is a syntax error:

    $ perl -w
    $b = "bus";
    eval reverse $b;
    print $@;
    __END__
    syntax error at (eval 1) line 2, at EOF
[download]

And if the code doesn't compile, eval will return undef.

-- Abigail