Bash: how to check process availability

If you have script which deploys some product / runs some service, you may need to check whether it’s actually started. For example:

#check if some process is running
if [ ps aux | grep $PROCESS_NAME -c == '0' ]; then
    echo Process not started
else
    echo Process started!
fi

#check if some application occupied some port
l_TELNET=echo "quit" | telnet 127.0.0.1 $PORT_NUMBER | grep "Escape character is"
if [ “$?” -ne 0 ]; then
     sleep 1
fi

But what if your script need to wait until application started? I suggest to use recurrent function to do that:

check_whether_service_started(){
  sleep 3
  if [ ps aux | grep $PROCESS_NAME -c == '0' ]; then
	echo Waiting for process to start...
	check_whether_service_started
  else
	echo Process is running.
  fi
}

It will wait for 3 seconds and recheck process availability until it will be running.