SQL & PL/SQL

Hi,

I want to be able to pass a variable back to the Unix script,and I have the following code

******************

sqlplus myuser/mypass << EOF
WHENEVER SQLERROR EXIT 41;
WHENEVER OSERROR EXIT 81;
execute pkonp.run_onp;
exit
EOF

ERRORCODE=$?

if [$ERRORCODE != 0] #test for successful onp
then
#Notify Administrator of ONP failure.
echo "ONP failure at `date`\n"
fi

******************
However, I am unable to get my PL/SQL to pass an error code back to SQL*Plus.

how do you trap an error in PL/SQL, and pass the error code to SQL*plus, so that SQL*Plus can then pass the error back to the Unix Shell script ?

Thank you very much.