See CGI on how to accept parameters in a CGI script. You should remove the manual CGI parsing from your script and use CGI for the query parsing.

There is no $? command in Perl. If you mean that you inspected the $? variable in Perl, then that means that the shell that runs the sqlplus command did complete without error. Most likely the user your webserver runs your program as does not have access to sqlplus or maybe the Oracle libraries are not available when the webserver runs sqlplus. You will have to debug this yourself, most likely by inspecting %ENV when you run your program from the command line and when you run it from the webserver.