Just to be different:

# $str defined elsewhere 
$str =~ s/\A
    (.{0,17})
    (.*)       # Normal rules about .* don't apply--we 
               # really do need everything that's left
\z/$1(?($2) \. \. \.)/x;
[download]

Update: Never mind. Doesn't work.

----
I wanted to explore how Perl's closures can be manipulated, and ended up creating an object system by accident.
-- Schemer

Note: All code is untested, unless otherwise stated