root@test:/home/test/shell# time=`uptime`
root@test:/home/test/shell# echo $time
22:07:03 up 1:02, 2 users, load average: 1.08, 0.98, 0.97
root@test:/home/test/shell# time=$(uptime)
root@test:/home/test/shell# echo $time
22:07:10 up 1:03, 2 users, load average: 1.15, 1.00, 0.98
root@test:/home/test/shell# sum=$[5+1]
root@test:/home/test/shell# echo $sum
6
root@test:/home/test/shell#
root@test:/home/test/shell# echo $((1+2))
3
