Use of Linux Regular expressions

Use of regular expressions

1.1 Creating an environment

Cat >q.txt<<eof

Oldboy Oldboy

Hellooldboy Hellooldboy

Awkoldboy Awkoldboy

Sedoldboy Sedoldboy

oldboyedu oldboyedu

Eof

Take out only the Oldboy line

grep "\boldboy\b" Q.txt

Instance 1-1 Reverse Reference

[Email protected]~]# # # # #第一个里程碑-Reverse reference (first protected and then used)

[Email protected]~]# echo 123456|sed-r ' s#. (..).. #\1#g '

34

[Email protected]/]# echo 123456|sed-r ' s# (.). (..). (.) #\1\2\3#g '

1346

1. * 0 or more times + 1 or more times? 0 or 1 times {} Customize several or several times to several times

1.2 Summary of regular expressions

Egrep/grep understand, simple look effect, result.

Egrep/grep-o the parameters to see exactly what the regular match is.

With Grep,egrep,sed-r,awk more powerful.

1.3 References to regular expressions

Mans grep

Infogrep

Mans 7 Glob

Linux Regular expression syntax

http://aresxin.blog.51.cto.com/4734097/1602624

Regular Expressions 30-minute introductory tutorial

Http://deerchao.net/tutorizls/regex/regex.htm.htm#mission

The use of 1.4 sed in regular expressions

Example 1-2 removing 644 or 0644 in/etc/hosts

Enter the environment: [[email protected] ~]# stat/etc/hosts

# # #方法一

[Email protected] ~]# stat/etc/hosts

[Email protected] ~]# Stat/etc/hosts|awk ' nr==4 ' |sed ' s#^.* (0# #g ' |sed ' s#/.*$# #g '

644

Method Two:

[[email protected] ~]# Stat/etc/hosts|awk ' nr==4 ' |sed-r ' s#^.*\ (0 (. *)/-.*$#\1#g '

644

# # #方法三 Awk

[Email protected] ~]# stat/etc/hosts

[[Email protected]~]# stat/etc/hosts |awk ' nr==4 ' |awk-f ' [0/] ' ' {print $} '

644

1.5 sed Reverse Reference remove/etc/hosts file permission plot

Example 1-3

# #找出oldboy a line in. txt that begins with M or N and ends with. or M

[Email protected]~]# cat Oldboy.txt

[[Email protected]~]# # # #第一个里程碑-M or N

[[email protected] ~]# grep "^[mn]" oldboy.txt

[Email protected]~]# # # #第二个里程碑-Find the end of. or M

[[email protected] ~]# grep "[. m]$" Oldboy.txt

[[Email protected]~]# ####[] There is no special meaning to the symbol special symbol in the expression.

[Email protected]~]# grep ". $" Oldboy.txt

[Email protected]~]# # # # #第三个里程碑-and

[[email protected] ~]# grep "^[mn].*[.m]$" Oldboy.txt

1.6 Remove the IP address and 10.0.0.255 of the network card

Example 1-4

[Email protected] ~]# #取出网卡的ip地址和10.0.0.255

[Email protected] ~]# ifconfig eth0

[Email protected] ~]# ifconfig eth0 |sed-n ' 2p '

[[email protected] ~]# ifconfig eth0 |sed-n ' 2p ' |sed-r ' S#^.*DR: (. *) Bc.*t: (. *) M.*$#\1#g '

10.0.0.200

[[email protected] ~]# ifconfig eth0 |sed-n ' 2p ' |sed-r ' S#^.*DR: (. *) Bc.*t: (. *) M.*$#\2#g '

10.0.0.255

[[email protected] ~]# ifconfig eth0 |sed-n ' 2p ' |sed-r ' S#^.*DR: (. *) Bc.*t: (. *) M.*$#\1\2#g '

10.0.0.20010.0.0.255

[[email protected] ~]# ifconfig eth0 |sed-n ' 2p ' |sed-r ' S#^.*DR: (. *) Bc.*t: (. *) m.*$#\1 \2#g '

10.0.0.200

1.7 Use awk to remove the IP address and 10.0.0.255 of the network card

Method Three Awk method

[Email protected] ~]# ifconfig Eth0|awk ' nr==2 '

[[email protected] ~]# ifconfig eth0|awk ' nr==2 ' |awk-f "[:]" ' {Print $13} '

10.0.0.200

[Email protected]~]# ifconfig eth0|awk ' nr==2 ' |awk-f ' [:]+ ' ' {print $4} '

10.0.0.200

10.0.0.255

[Email protected]~]# ifconfig eth0|awk-f "[:]+" ' Nr==2{print $4,$6} '

10.0.0.20010.0.0.255

Method Four

Remove IP address and 255.255.255.0

[Email protected] ~]# ifconfig eth0 |awk ' nr==2 ' |awk-f "[:]+" ' {print $4, $NF} '

10.0.0.200

255.255.255.0

Method Five

Take IP address permissions

[Email protected] ~]# ifconfig eth0

[[email protected] ~]# ifconfig eth0 |awk-f "addr: ' Nr==2{print $} '

[[email protected] ~]# ifconfig eth0 |awk-f "Addr:|bcast: ' Nr==2{print $} '

10.0.0.200

1.8 + Usage

Re-recognize the next + consecutive occurrences

Example 1-5

Usage One

[Email protected] ~]# echo "##########[email protected]@@@@@@@@@2"

##########[email protected]@@@@@@@@@2

[Email protected] ~]# echo "##########[email protected]@@@@@@@@@2" |grep "[#@]"

##########[email protected]@@@@@@@@@2

[Email protected] ~]# echo "##########[email protected]@@@@@@@@@2" |grep "[#@]"-O

#

Usage Two

[Email protected] ~]# echo "##########[email protected]@@@@@@@@@2" |egrep "[#@]+]

##########[email protected]@@@@@@@@@2

[[email protected] ~]# echo "##########[email protected]@@@@@@@@@2" |egrep "[#@]+"-O

##########

@@@@@@@@@@

[Email protected] ~]#

[Email protected] ~]# echo "##@@@@@@###@@@@#####[email protected]@@###@@@@@@@2" |egrep "[#@]+]

##@@@@@@###@@@@#####[email protected]@@###@@@@@@@2

[Email protected] ~]# echo "##@@@@@@########[email protected]@@###@@@@@@@2" |egrep "[#@]+]

##@@@@@@########[email protected]@@###@@@@@@@2

[[email protected] ~]# echo "##@@@@@@########[email protected]@@###@@@@@@@2" |egrep "[#@]+"-O

##@@@@@@########

@@@###@@@@@@@

1.9 [] use in regular expressions

###[] Regular expressions will assume that the contents of the brackets are the same ABC

# # #1. In my basket

# # #2. Not in my basket.

Example 1-6

[[email protected] ~]# echo "##########[email protected]@@@@@@@@@2" |awk-f "[#@]+" ' {print $} '

1

[Email protected] ~]# ifconfig eth0 |awk ' nr==2 ' |sed ' s#:# #g '

Use of 1.10 cut

Method Four-cut

# #先把冒号替换为空格取第13列

Example 1-7

[Email protected] ~]# ifconfig eth0 |awk ' nr==2 ' |sed ' s#:# #g '

[Email protected] ~]# ifconfig eth0 |awk ' nr==2 ' |sed ' s#:# #g ' |cut-d ' "-f13

10.0.0.200

# #先通过: Split, then split by space

[Email protected] ~]# ifconfig eth0 |awk ' nr==2 ' |cut-d ":"-f2

10.0.0.200

Bcast

[Email protected] ~]# ifconfig eth0 |awk ' nr==2 ' |cut-d ":"-f2|cut-d ""-f1

10.0.0.200

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Use of Linux Regular expressions