Network - netcat (nc, ncat)

Simple if statement

TOMCAT_PORT=6006
if [[ $(nc -z localhost ${TOMCAT_PORT}) -eq 0 ]]; then
	echo "Tomcat is up"
else
	echo "Tomcat is shutdown"
fi

While Statement

• while A port may be not open but still locked by a process. See the second statement

while [[ $(nc -z localhost ${TOMCAT_PORT}) -eq 1 ]]; do
        echo "Waiting for the tomcat port ${INFA_TOMCAT_PORT} to be closed before starting"
	sleep 5 # wait 5 second before check again
done
###############################################################
# It seems that a port may returns 0 even if a process is still bound to a port
###############################################################
while [[ ! $(netstat -t|grep ${TOMCAT_PORT} | wc -l) -eq 0 ]]; 
do
	echo "Waiting for the tomcat port ${INFA_TOMCAT_PORT} to be closed before starting"
	sleep 5 # wait 5 second before check again
done

Wait function with timeout

# usage
# wait_for_service service_name port
wait_for_service() {
  local SERVICE_NAME=$1
  local PORT=$2
  SERVICE_WAIT_TIMEOUT_SEC=20
  echo "Waiting for $SERVICE_NAME to start..."
  local CURRENT_WAIT_TIME=0

  while [[ $(echo | nc -w1 localhost $PORT >/dev/null 2>&1 ;echo $?) -ne 0 ]]; do
      printf '.'
      sleep 1
      if [ $((++CURRENT_WAIT_TIME)) -eq $SERVICE_WAIT_TIMEOUT_SEC ]; then
        printf "\nError: timed out while waiting for $SERVICE_NAME to start.\n"
        exit 1
      fi
  done
  printf '\n'
  echo "$SERVICE_NAME has started";
}

Wait for it

For a full functional example, see wait-for-it.sh