sed substitute with variable

var=FpingLocation

conf=$(whereis zabbix_server | sed "s/^.* //g")
echo $conf

fping=$(whereis fping | cut -d' ' -f2)
echo $fping

Check if the replacement works:

sed "s|^.*$var=.*$|$var=$fping|" $conf | grep "^$var"

Replace:

sed -i "s|^.*$var=.*$|$var=$fping|" $conf | grep "^$var"

Final check:

grep "^$var" $conf