Calculate the line number to comment out, sed

#look just below logout($user) function
cd /usr/share/zabbix/include/classes/api/services
#show some output of active configuration
grep -n -A5 "public function logout" CUser.php
#backup configuration
cp CUser.php ~
#calculate line to comment out
ln=$(grep -n -A5 "public function logout" CUser.php | grep ZBX_API_ERROR_PARAMETERS | egrep -o "^[0-9]+")
#echo line number
echo "$ln"
#uncomment line
sed -i "$ln {s/^/#/}" CUser.php
#show what has been commented
grep -n -A5 "public function logout" CUser.php