echo back character, that is the character to the screen output
[root@localhost ~]# [root@localhost ~]# a=1 [root@localhost ~]# aa=2 [root@localhost ~]# echo a a [root@localhost ~]# echo aa aa [root@localhost ~]# [root@localhost ~]#
echo back is variable, then the screen output to the value of the variable
[root@localhost ~]# [root@localhost ~]# echo $a 1 [root@localhost ~]# echo $aa 2 [root@localhost ~]#