Linux大神养成之正则表达式（grep，sed）

Linux大神养成之正则表达式

grep命令

参数：

• -A后面加数字，代表after，表示把该行的后续n行也列出来
• -B后面加数字，代表befer，表示把改行的前面n行也列出来

$ dmesg | grep -n -A3 -B2 --color=auto 'eth'

1. 查找特定字符串

$ cat -n 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  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

$ grep -n 'the' regular_express.txt 

8:I can’t finish the test.^M
12:the symbol ‘*’ is represented as start.
15:You are the best is mean you are the no. 1.
16:The world is the same with “glad”.
18:google is the best tools for search keyword.

2.利用中括号来查找集合字符

$ grep -n 't[ae]st' regular_express.txt 

8:I can’t finish the test.^M
9:Oh! The soup taste good.^M
查找包含tast或test的字符的句子

$ grep -n '[^g]oo' regular_express.txt 

2:apple is my favorite food.
3:Football game is not use feet only.
18:google is the best tools for search keyword.
19:goooooogle yes!
^反向选择，即非的意思，就是oo的前面的字母不是g的

$ grep '[^a-z]oo' -n regular_express.txt 

3:Football game is not use feet only.
oo前面是非小写的

3.行首与行尾符^$

$ grep -n '^[a-z]' regular_express.txt


2:apple is my favorite food.
4:this dress doesn’t fit me.
10:motorcycle is cheap than car.
12:the symbol ‘*’ is represented as start.
18:google is the best tools for search keyword.
19:goooooogle yes!
20:go! go! Let’s go.
^放在外面表示行首的意思，表示选出以小写字母开始的行

$ grep -n '^[^a-zA-Z]' regular_express.txt 

1:”Open Source” is a good mechanism to develop programs.
21:# I am VBird
不是以字母开头的行

$ grep -n '\.$' 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.
10:motorcycle is cheap than car.
11:This window is clear.
12:the symbol ‘*’ is represented as start.
15:You are the best is mean you are the no. 1.
16:The world is the same with “glad”.
17:I like dog.
18:google is the best tools for search keyword.
20:go! go! Let’s go.
$表示行尾，表示以 ‘.’ 结尾的行，其中 ‘\’ 是转义符

$ grep -v '^$' /etc/syslog.conf | grep  '^#'

# Log all kernel messages to the console.
# Logging much else clutters up the screen.
#kern.* /dev/console
# Log anything (except mail) of level info or higher.
# Don’t log private authentication messages!
# The authpriv file has restricted access.
# Log all the mail messages in one place.
# Log cron stuff
# Everybody gets emergency messages
# Save news errors of level crit and higher in a special file.
# Save boot messages also to boot.log
选出非空行的，然后在选出以#开头的文字

4.任意一个.和重复的*


$ grep -n 'g..d' regular_express.txt


1:”Open Source” is a good mechanism to develop programs.
9:Oh! The soup taste good.^M
16:The world is the same with “glad”.
‘g..d’表示g和d中间有两个连续任意字符的都可以匹配

$ grep -n 'goo*g' regular_express.txt 

18:google is the best tools for search keyword.
19:goooooogle yes!
‘goo*g’前一个o必须有，后一个’o *’表示一个或多个，所以为至少一个o

$ grep -n g.*g regular_express.txt 

1:”Open Source” is a good mechanism to develop programs.
14:The gd software is a library for drafting programs.^M
18:google is the best tools for search keyword.
19:goooooogle yes!
20:go! go! Let’s go.
表示由g开头g结尾的行

$ grep -n '[0-9][0-9]*' regular_express.txt

5:However, this dress is about $ 3183 dollars.^M
15:You are the best is mean you are the no. 1.
表示以数字开头，后面有0个到任意个数字的行

5.限定连续RE字符的范围{}


$ grep -n 'o\{2\}' 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.
9:Oh! The soup taste good.^M
18:google is the best tools for search keyword.
19:goooooogle yes!
表示包含两个‘o’的行

$ grep -n 'go\{2,\}g' regular_express.txt

18:google is the best tools for search keyword.
19:goooooogle yes!
g和g中间包含两个以上的o

sed工具

参数：

• -n 安静模式，只列出经过特殊处理的行
• -i 直接修改文件内容，而不是屏幕输出
• -e 直接在命令行模式上sed动作编辑
• -f sed动作写在一个文件中
• -r扩展正则语法

函数参数;

• a 新增
• c 替换
• d 删除
• i 插入
• p打印

• s 替换（和c的不同看练习）

  1.以行为单位进行新增/删除

$ nl /etc/passwd | sed '2,5d'

1 root:x:0:0:root:/root:/bin/bash
 6  sync:x:5:0:sync:/sbin:/bin/sync
 7  shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
 8  halt:x:7:0:halt:/sbin:/sbin/halt
 9  mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
 PS:表示删除第2-5行

$ nl /etc/passwd | sed '2a Drink tea or .....\ 
> drink bear ?'

1 root:x:0:0:root:/root:/bin/bash
2 bin:x:1:1:bin:/bin:/sbin/nologin
Drink tea or …..
drink bear ?
3 daemon:x:2:2:daemon:/sbin:/sbin/nologin
4 adm:x:3:4:adm:/var/adm:/sbin/nologin
5 lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
PS:给第二行之后添加后面的字符串，用’\’表示新行进行增加

2.以行为单位进行替换显示的功能

$ nl /etc/passwd | sed '2,5c No 2-5 number'


1 root:x:0:0:root:/root:/bin/bash
No 2-5 number
6 sync:x:5:0:sync:/sbin:/bin/sync
7 shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
PS:将2-5行替换成‘No 2-5 number’

$ nl /etc/passwd | sed -n '2,5p'

2 bin:x:1:1:bin:/bin:/sbin/nologin
 3  daemon:x:2:2:daemon:/sbin:/sbin/nologin
 4  adm:x:3:4:adm:/var/adm:/sbin/nologin
 5  lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
 PS：注意这里 '-n' 安静模式，只列出特殊处理的行

$ /sbin/ifconfig eth1

eth1 Link encap:Ethernet HWaddr 6C:AE:8B:21:98:9B
inet addr:10.209.102.43 Bcast:10.209.102.127 Mask:255.255.255.128
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:47103902950 errors:0 dropped:7743 overruns:7743 frame:0
TX packets:11073405019 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:59771891524541 (54.3 TiB) TX bytes:810933823454 (755.2 GiB)

$ /sbin/ifconfig eth1  | grep 'inet addr'

     inet addr:10.209.102.43  Bcast:10.209.102.127  Mask:255.255.255.128

$ /sbin/ifconfig eth1  | grep 'inet addr' | sed 's/^.*addr://g'

10.209.102.43 Bcast:10.209.102.127 Mask:255.255.255.128
PS:”sed ‘s/要替换字符/新字符/g’”

$ /sbin/ifconfig eth1  | grep 'inet addr' | sed 's/^.*addr://g' | sed 's/Bcast.*//g'

10.209.102.43
PS:其实就相当于hostname -i

$ cat /etc/man.config | grep 'MAN' | sed 's/#.*$//g' | sed '/^$/d'

MANPATH /usr/share/man
MANPATH /usr/man
MANPATH /usr/local/share/man
MANPATH /usr/local/man
MANPATH /usr/X11R6/man
MANPATH_MAP /bin /usr/share/man
MANPATH_MAP /sbin /usr/share/man
MANPATH_MAP /usr/bin /usr/share/man
MANPATH_MAP /usr/sbin /usr/share/man
PS:先选出包含‘MAN’的行，然后替换掉’#’开头的，即注释，然后把空行删除，注意最后的空行表示是写在一对 ‘/ /’中

• 直接修改文件（危险操作）

 $ sed -i 's/\.$/\!/g' regular_express.txt 

PS:直接把原文件中的‘.’结尾的全部替换成‘！’

 $ sed -i '$a # This is a tese' regular_express.txt 

PS:给文章的最后一行添加一句话