That's just ugly.
Ugly? It's true that one doesn't automatically get a printout of the last expression evaluated (one has to ask for it with p or x or print, etc.), but getting readline/history, trace mode option, and the joy of x alone makes this well worth it, IMO.
BTW, I'm not sure what you had intended with
perl -wlne'print eval//$@//""'
but it bombs:
% perl -wlne 'print eval//$@//""'
Warning: Use of "eval" without parentheses is ambiguous at -e line 1.
Scalar found where operator expected at -e line 1, near "//$@"
(Missing operator before $@?)
syntax error at -e line 1, near "//$@"
Search pattern not terminated at -e line 1.
the lowliest monk |