in reply to
output of one program doesn't show in another on server
What AnomalousMonk said. What happens there is that length evaluates @ret in scalar context which gives either 0 or 1 and then takes the length of this string which is 1 in both cases.
Your real problem though is one with the working directory as Apache doesn't change it to that where the CGI lives so ./runthis.pl is not found. Try an absolute path or FindBin (ISTR the latter had some problems with CGI environments as well but it's worth a try)