1.什么是正则式表达
正则式表达就是处理字符的方法，是以行为单位来进行字符串的处理行为。对于管理员来说，正则式表达是不得不学的好东西。这里需要记住的是，正则式表达和通配符没有任何的关系。
2.grep的一些高级参数
2.1.基础正则式表达练习
首先在鸟哥的网站上进行数据的下载。
zhangsan@Aliyun:~$ wget http://linux.vbird.org/linux_basic/0330regularex/regular_express.txt
zhangsan@Aliyun:~$ vim regular_express.txt
1 "Open Source" is a good mechanism to develop programs.
2 apple is my favorite food.
3 Football game is not use feet only.
4 this dress doesn't fit me.
5 However, this dress is about $ 3183 dollars.^M
6 GNU is free air not free beer.^M
7 Her hair is very beauty.^M
8 I can't finish the test.^M
9 Oh! The soup taste good.^M
10 motorcycle is cheap than car.
11 This window is clear.
12 the symbol '*' is represented as start.
13 Oh! My god!
14 The gd software is a library for drafting programs.^M
15 You are the best is mean you are the no. 1.
16 The world <Happy> is the same with "glad".
17 I like dog.
18 google is the best tools for search keyword.
19 goooooogle yes!
20 go! go! Let's go.
21 # I am VBird
22
上面的内容就是鸟哥连接的内容了。
首先要进行特定的字符串的查找，如下所示。
zhangsan@Aliyun:~$ grep -n 'the' regular_express.txt
8:I can't finish the test.
12:the symbol '*' is represented as start.
15:You are the best is mean you are the no. 1.
16:The world <Happy> is the same with "glad".
18:google is the best tools for search keyword.
其次，我们利用中括号进行查找
zhangsan@Aliyun:~$ grep -n 't[ea]st' regular_express.txt
8:I can't finish the test.
9:Oh! The soup taste good.
通过这个例子，可得知[]的作用就是替换[ea]表示e和a都可以。
行首^与行尾$
此外，我们也可以通过行首字符^与行尾字符$去掉一些特殊的字符
# ^ 代表的是以tom为开头的字条
zhangsan@Aliyun:~$ grep '^tom' passwd
tom sys:x:3:3:sys:/dev:/usr/sbin/nologin
# $ 代表的是以tom为结尾的字条
zhangsan@Aliyun:~$ grep 'tom$' passwd
games:x:5:60:games:/usr/games:/usr/sbin/nologintom
如果我想要找出哪一行是空白行，我的操作就是：
zhangsan@Aliyun:~$ grep -n '^$' regular_express.txt
22:
任意字符.与重复字符*
zhangsan@Aliyun:~$ grep -n 'g..d' regular_express.txt
1:"Open Source" is a good mechanism to develop programs.
9:Oh! The soup taste good.
16:The world <Happy> is the same with "glad".
限定连续RE字符{}
# 查找tm之间有四个o的字符
zhangsan@Aliyun:~$ grep 'to\{4\}m' passwd
toooom sys:x:3:3:sys:/dev:/usr/sbin/nologin
# 查找tm之间有4~9个o的字符
zhangsan@Aliyun:~$ grep 'to\{4,9\}m' passwd
toooom sys:x:3:3:sys:/dev:/usr/sbin/nologin
tooooooooomsync:x:4:65534:sync:/bin:/bin/sync
tooooomman:x:6:12:man:/var/cache/man:/usr/sbin/nologin
3.sed工具
sed命令能够将满足要求的字符找出来并进行修改。
zhangsan@Aliyun:~$ sed '1,2d' hosts
# 删除hosts 文件的第一行与第二行
# sed把文件放到内存，然后修改，只在内存修改
zhangsan@Aliyun:~$ sed -i '1,2d' hosts
# 直接修改到文件中
4.awk好用的数据处理工具
awk命令能够帮助我们找到感兴趣的内容然后排版，其操作的格式为：awk -F ‘条件{操作}’ 文件
zhangsan@Aliyun:~$ ifconfig eth0
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 162.17.172.171 netmask 255.255.240.0 broadcast 162.16.165.255
ether 00:16:3e:10:b4:c7 txqueuelen 1000 (Ethernet)
RX packets 41449753 bytes 9972007192 (9.9 GB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 41068356 bytes 6352574318 (6.3 GB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
# 抓取 162.17.172.171 这一段
zhangsan@Aliyun:~$ ifconfig eth0 | grep 'inet' | awk -F" " '{print $2}'
162.17.172.171
来源：CSDN
作者：kaitokuroba_777
链接：https://blog.csdn.net/qq_21481459/article/details/104305045