secUser=`who am i | awk '{print $1}'` 
#echo $secUser 
su $secUser -c 指令> > /dev/null 2>1  #這一條命令的執行權限是臨時的，只在本條語句起作用 
id -u # 結果為0，還是root用戶權限 

 -c, --command COMMAND   pass COMMAND to the invoked shell
 -h, --help     display this help message and exit
 -, -l, --login    make the shell a login shell
 -m, -p,
 --preserve-environment  do not reset environment variables, and
        keep the same shell
 -s, --shell SHELL    use SHELL instead of the default in passwd