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| 管道符号： 将前面命令的输出送给后面的命令作为输入 借花献佛，中间人

grep 是文本过滤命令，默认情况下符合要求（匹配的）会整行显示出来

^d 代表一行里以d开头

[root@localhost log]# ls -l|grep  "^d"
drwxr-xr-x. 2 root  root       176 Sep  8  2017 anaconda
drwx------. 2 root  root        23 Sep  8  2017 audit
drwxr-xr-x  2 mysql mysql      103 Oct  6  2017 mysql
drwx------  2 nginx nginx      159 Nov 13 10:14 nginx
drwx------. 2 root  root         6 Jun 10  2014 ppp
drwxr-xr-x. 2 root  root         6 Sep  8  2017 rhsm
drwxr-xr-x  2 root  root       139 Nov 27 09:40 sa
drwxr-xr-x. 2 root  root        23 Sep  8  2017 tuned
[root@localhost log]#
[root@localhost log]# ll|grep "^d"|wc -l
8
[root@localhost log]# 
[root@localhost log]# ll|grep "^-"|wc -l
38
[root@localhost log]# 

[root@localhost log]# exit 退出当前bash返回到父bash
exit
[root@localhost log]#