如果某些内容正在运行，如何检入bash脚本，如果是，则退出

I have a script that runs every 15 minutes but sometimes if the box is busy it hangs and the next process will start before the first one is finished creating a snowball effect. How can I add a couple lines to the bash script to check to see if something is running first before starting?I have a script that runs every 15 minutes but