check multiple ports using netcat nc

Question

I'm using the follow to wait till a port opens.

while ! nc -z 127.0.0.1 8080; do sleep 0.1; done

how can the above be modified to check multiple ports. So the script should stop only when all ports are occupied, e.g. 8080, 8081, and 8082.

Answer 1

You need to run nc separately for each port:

while ! (nc -z 127.0.0.1 8080 && nc -z 127.0.0.1 8081 && nc -z 127.0.0.1 8082)
    do sleep 0.1
done

(split across multiple lines for readability)

This uses a shell subshell with a list of commands with a logical "and" && operator; the second nc command is only run if the first one succeeded, etc.; once all nc commands are successful, the exit status of the subshell is true, this is negated by the ! and the while loop terminates.