bash - How to wait for an open port with netcat?

Question

I'm trying to do a custom dockerfile with jenkins on it. I would to wait until port 8080 is open instead of doing an ugly 'sleep 60' with netcat but I'm not very confident with bash scripts and netcat.

Here is an example of what i'm trying to do:

#!/bin/bash
 
opened=0
 
while [ "$opened"  == "0" ]; do
  echo "Waiting jenkins to launch on 8080..."
  nc -vz localhost 8080
done
 
echo "Jenkins launched"

Answer 1

You can't set netcat to wait until some port is open, so you have to add part for waiting before next check is made. Try this:

#!/bin/bash

echo "Waiting jenkins to launch on 8080..."

while ! nc -z localhost 8080; do   
  sleep 0.1 # wait for 1/10 of the second before check again
done

echo "Jenkins launched"