How to know user identity.

id
id (1p) - return user identity
id (1) - print user identity

root id is 0
id -u return 0 then u r root else not.

e.g
[root@vikas 18-feb]# id -u
0
[root@vikas 18-feb]# id
uid=0(root) gid=0(root) groups=0(root),1(bin),2(daemon),3(sys),4(adm),6(disk),10(wheel)
[root@vikas 18-feb]# su vikas
[vikas@vikas 18-feb]$ id
uid=500(vikas) gid=500(vikas) groups=500(vikas)
[vikas@vikas 18-feb]$ id -u
500
[vikas@vikas 18-feb]$ su

if [ `id -u` = "0" ] ; then
echo "u r root"
else
echo " u r not root"
fi