Hi,
On isql you can execute the procedure with the procedure name and argument/s. If you want to execute only a part of the entire procedure, you may comment the unrequired part through vi editor and save the file. The command to create the procedure is :r <filename>
Thereafter, you may try executing the procedure from the same isql window and you can check the result. Similarly you can go step by step to check the complete procedure.
I am not sure whether this is what you are looking for. Pls write to me in case you want something else.
Regards,
Joson