ubuntu add or change config file entry

a.sh

function add_or_change {
        TARGET_KEY=$1
        REPLACEMENT_VALUE=$2
        CONFIG_FILE=$3
        if grep -e "^\s*$TARGET_KEY\s*=" "$CONFIG_FILE"; then
           sed -i 's/^\('"$TARGET_KEY"'\s*=\s*\).*$/\1'"$REPLACEMENT_VALUE"'/' $CONFIG_FILE
           grep -e "^\s*$TARGET_KEY\s*=" "$CONFIG_FILE"
        else
           echo "$TARGET_KEY=$REPLACEMENT_VALUE" >> "$CONFIG_FILE"
        fi
}