下面是我的脚本
#!/bin/bash

this_pid=$$
ps -ef | grep nginx | grep -v grep | grep -v $this_pid

if [ $? -eq 0 ];then
echo "Nginx is running well"
else
systemctl start nginx
echo "Nginx is down,start it"
fi

在我将nginx服务停掉之后，执行上述脚本
[vagrant@docker-host shell]$ sudo bash -x nginx_daemon.sh

• this_pid=9071
• grep nginx
• grep -v grep
• grep -v 9071
• ps -ef
  root 9069 8446 0 16:06 pts/0 00:00:00 sudo bash -x nginx_daemon.sh
• ‘[’ 0 -eq 0 ‘]’
• echo 'Nginx is running well’
  Nginx is running well

$$获取到的进程id和实际的id不一样