how to use if inside a command in bash script?

I am writing a script in bash, and i have a problem with it :

select opt in "${options[@]}" do case $opt in "1) Check Cassandra Status.") ssh skyusr@"$IP" "export JAVA_HOME=/opt/mesosphere && /var/lib/mesos/slave/slaves/*/frameworks/*/executors/*/runs/latest/apache-cassandra-3.0.10/bin/nodetool -p 7199 status" | sed -n '6,10p' | awk '{print $1,$2}' | DN="$(grep DN)" | [[if [[!DN]]; echo "All Good" else "Node(s) "$DN" is Down" ;fi]] ;; "2) Run Repair on all nodes.") echo "you chose choice 2" ;; "3) Run Refresh on specific keyspace/Table.") echo "you chose choice 3" ;; "4) Optional") echo "This option disabled" ;; "Quit") break ;; *) echo invalid option;; esac done

All was working until i added this if command, i need to echo a message if "$DN" is empty else echo another message .

Please help !!!!