linux 如何判断当前用户

linux 中，如何判断当前用户是否是root  呢？

判断当前用户是否是root

#---------------------------- root user check ---------------------start   
if [ `id -u` -ne 0 ]; then  
    echo "Please re-run ${this_file} as root."  
    exit 1   
fi   
#---------------------------- root user check ---------------------end  
 

if [ x"$USER" = x"" ];then  
    if  id |grep "^uid=0(root)">/dev/null ;then  
        :   
    else  
        echo "Please rerun `basename $0` as root ."  
        exit 1   
    fi   
else  
    if [ ! x"$USER" = x"root" ];then  
        echo "Please rerun `basename $0` as root ."  
        exit 1   
    fi   
fi  
 

#=============== check current user start ================   
if [ ! $USER = root  ];then  
    echo "Please rerun this script as root ."  
    exit 1   
fi   
#=============== check current user end ================  
 

#!/bin/sh   
if  id |grep "^uid=0(root)">/dev/null ;then  
    echo is  root   
else  
    echo not  root   
fi   
 

check_user(){   
    if [ $UID -ne 0 ];then  
        echo "Current user is not ROOT."  
        echo "Please rerun the installer as Root user."  
        exit 11   
    fi   
}