hi,
as for catching errors in sql this might help.
u can have an exception block in the sqplus block and catch the return code once u come out of the block.
so if u have an error u can abort the script so that the next in line functions r not executed.

....script
.....
....
spout=`sqlplus -s $UP <<EOJ

SET HEAD OFF
SET AUTOPRINT OFF

WHENEVER SQLERROR EXIT;
(this way if u have an sql error u get an exit condition)
(either have this or catch it in the excepton block)

ALTER TRIGGER XX ENABLE;

CREATE ........ON ........(......)
TABLESPACE .......... PCTFREE 10
STORAGE(INITIAL 104K NEXT 104K PCTINCREASE 0 );

DECLARE

v_alter_statement VARCHAR2(255);

CURSOR c_constraint_name IS
SELECT constraint_name
FROM dba_constraints
WHERE table_name = 'YYYY';

BEGIN
FOR REC IN c_constraint_name
LOOP
v_alter_statement := 'ALTER TABLE YYYY';
v_alter_statement := v_alter_statement || ' ENABLE CONSTRAINT ';
v_alter_statement := v_alter_statement || REC.constraint_name;
DBMS_UTILITY.EXEC_DDL_STATEMENT(v_alter_statement);
END LOOP;


Exception

when OTHERS then
Rollback;
dbms_output.put_line ('Script failed : Sqlcode: ' || SQLCODE || ' Error message :' ||
SQLERRM);
return;


END;
/
EOJ`

....pl sql ends here!!
you have to define FATAL and sucess in ur env file afaik!

ret_code=$?

echo "$spout" >> ${logfile}

if [ $ret_code -ne $SUCCESS ]
then
cat ${logfile}
echo
echo
echo Script Failed.
echo "Script Ended : " `date`
echo

exit $FATAL
fi

if test $ret_code -ne 0
then
cat ${logfile}
echo
echo
echo Script Failed.
echo "Script Ended : " `date`
echo

exit ${OXYGEN_FATAL}
fi

# no errors.
cat ${logfile}
echo
echo
echo Script completed sucessfully
echo "Script Ended : " `date`
echo


exit $SUCCESS



well this is just an example script!
hope this helps.
Regards
Manish