利用linux shell脚本监控py进程是否存在

#!/bin/sh
PWD=`pwd`
while true;do
    ps -fe|grep bcdn.py |grep -v grep
    if [ $? -ne 0 ] # 判断进程是否存在
    then
        echo "start process....."
        cd /root
        python bcdn.py
       cd ${PWD}
    else
        echo "bcdn.py is running....."
    fi
    sleep 60 #延时60秒继续循环
done