Example wait for script

wait_for.sh

#!/usr/bin/env bash

STOP_TIME=`date -d "now + 30 seconds" +%s`
# loop until we get a connection
until nc -z localhost 3306
do
  # if current time is > STOP_TIME, timeout has been exceeded so exit
  if [[ `date +%s` -gt $STOP_TIME ]]; then
    echo Timed out waiting for connection
    exit 1
  fi
  sleep 1
done

echo Successfully connected