The grep command is detailed

Reference Links:

Http://www.cnblogs.com/ggjucheng/archive/2013/01/13/2856896.html

the grep family includes grep, Egrep, and Fgrep. Egrep and Fgrep commands are only a small difference from grep.

Egrep is the extension of grep, which supports more re metacharacters , and fgrep is fixed grep or fast grep, which regards all the letters as words, that is to say, The metacharacters in a regular expression represents a literal meaning back to itself, no longer special .

Linux uses the GNU version of grep. It is more powerful and can use the Egrep and FGREP functions with the-G,-e,-f command line options.

grep common usage:

-A: binary files are searched for data in the form of a text file

-C: Calculates the number of ' search string ' found

-I : ignores case differences , so case is considered the same

-N: Output line number by the way

- V: Reverse selection , which shows the line without the ' search string ' content!

--color=auto: Can be found in the keyword part of the color display OH !

eg

Remove the/etc/passwd, where Root is present.

[[email protected] ~]# grep root/etc/passwd

Root:x:0:0:root:/root:/bin/bash

Operator:x:11:0:operator:/root:/sbin/nologin

Remove the/etc/passwd, which is the root row, and display the line numbers of the rows in/etc/passwd

[Email protected] ~]# grep-n root/etc/passwd

1:root:x:0:0:root:/root:/bin/bash

11:operator:x:11:0:operator:/root:/sbin/nologin

Show the last three lines of the keyword with the first two lines

[Email protected] ~]# dmesg |grep-n-a3-b2 ' eth '

476-udev:starting version 147

477-piix4_smbus 0000:00:01.3:smbus Base Address Uninitialized-upgrade BIOS or use force_addr=0xaddr

478:initialising Xen Virtual Ethernet driver.

479-alloc Irq_desc for 928 on node 0

480-alloc Kstat_irqs on Node 0

481-alloc Irq_desc for 927 on node 0

grep tar * searches the current directory for lines with tar, displaying rows and files

grep-r tar * searches the current directory and its subdirectories for rows with tar, displaying rows and files

grep-l-R Tar * searches the current directory and its subdirectories for a file with a tar line, but does not display matching rows, only matching files are displayed

grep and regular expressions

[] There are a few bytes in it, he would like to represent a "one" byte

[[email protected] ~]# grep-n "t[ae]st" Agc.txt #只能匹配a或e, cannot match ae simultaneously

4:i can ' t finish the test.

5:oh! The soup taste good.

inverse selection of the character class [^] want to search for a line with Oo, but do not want oo preceded by G

[Email protected] ~]# grep-n [^g]oo agc.txt

7:apple is my favorite food.

8:football game isn't use feet only.

9:google is the best tools for search keyword. #有一个too

10:goooooogle yes! #这个oo前面还有o

Don't want lowercase/uppercase/numeric characters in front of OO

grep-n [^a-za-z0-9]oo Agc.txt

Want to get the line with numbers

[Email protected] ~]# grep-n [0-9] Agc.txt

6:oh! The soup teaste good 9.

Beginning of line with trailing bytes ^ $

List only the lines that begin with the

[Email protected] ~]# grep-n "^the" Agc.txt

5:the soup taste good.

6:the Soup Teaste Good 9.

List only lines beginning with uppercase characters

[Email protected] ~]# grep-n "^[a-z]" Agc.txt

4:i can ' t finish the test.

8:football game isn't use feet only.

To list lines that do not begin with the English alphabet

[[email protected] ~]# grep-n "^[^a-za-z]" Agc.txt # character class reverse selection [^]

1:9tar

Take it out? End of Line

[Email protected] ~]# grep-n "? $" agc.txt

2:ddddddddddddd?

remove the line that ends with. because the decimal point has a special meaning, you need to escape escaping　　　　

[Email protected] ~]# grep-n "\.$" Agc.txt

4:i can ' t finish the test.

8:football game isn't use feet only.

9:google is the best tools for search keyword.

Find Blank Lines

[Email protected] ~]# grep-n "^$" Agc.txt

8:

Any one of the bytes. With repeating bytes *

. (decimal point): Represents "must have an arbitrary byte " meaning;

* (asterisk): represents "repeating the previous character, 0 to infinity " meaning, for the combined form

Find out g?? A string of D

[Email protected] ~]# grep-n "G.. D "Agc.txt

5:the Soup Taste good

6:the Soup Teaste Good 9

Want to list data with Oo, OOO, oooo, etc.

Analysis:

* Represents the meaning of "repeating 0 or more preceding RE characters", so "o*" stands for: "Having empty bytes or an O or more bytes ",

Therefore, " grep-n ' o* ' Regular_express.txt" will print out all the data on the terminal !

So, when we need a "minimum of two + O" strings, we need ooo*

[Email protected] ~]# grep-n "ooo*" Agc.txt

5:the Soup Taste good

6:the Soup Teaste Good 9

7:apple is my favorite foo

9:football game isn't use feet only.

10:google is the best tools for search keyword.

11:goooooogle yes!

Want string start and end is G, but two g can only exist between at least one o, that is Gog, Goog, Gooog ....

[Email protected] ~]# grep-n "Goo*g" Agc.txt

10:google is the best tools for search keyword.

11:goooooogle yes!

Find the line where G begins with G and the characters are optional

[[email protected] ~]# grep-n "G.*g" Agc.txt #. * The RE means that any character is very common

8:gg

10:google is the best tools for search keyword.

11:goooooogle yes!

Find the "any number" line, because there are only numbers, so

[Email protected] ~]# grep-n "[0-9][0-9]*" Agc.txt

1:9tar

6:the Soup Teaste Good 9

Qualifying Continuous RE character range {}

For example, I want to find out two to five o continuous string, how to do? This is the time to use the qualified character {}. But since the symbol {and} is of special significance in the shell , we have to use the character \ To make him lose special meaning .

The syntax for {} is this, to find two strings of O

[[email protected] ~]# grep-n "o\{2\}" Agc.txt

5:the Soup Taste good

6:the Soup Teaste Good 9

7:apple is my favorite foo

9:football game isn't use feet only.

10:google is the best tools for search keyword.

11:goooooogle yes!

To find the G followed by 2 to 6 O, and then followed by a G string

[Email protected] ~]# grep-n "Go\{2,6\}g" Agc.txt

10:google is the best tools for search keyword.

11:goooooogle yes!

Want to be 2 o GOOOO....G

[Email protected] ~]# grep-n "Go\{2,\}g" Agc.txt

10:google is the best tools for search keyword.

11:goooooogle yes!

Extended grep (GREP-E or Egrep):

The main benefit of using the extended grep is the addition of additional regular expression meta-character sets.

Print All rows that contain NW or EA

[Email protected] ~]# egrep "nw| EA "Agc.txt

Northwest NW Charles Main 3.0.98 3 34

Eastern EA TB Savage 4.4.84 5 20

[Email protected] ~]# grep-e "nw| EA "Agc.txt

Northwest NW Charles Main 3.0.98 3 34

Eastern EA TB Savage 4.4.84 5 20

For standard grep, extended option-E is automatically enabled if \,grep is preceded by an extension metacharacters.

[[email protected] ~]# grep "nw\| EA "Agc.txt

Northwest NW Charles Main 3.0.98 3 34

Eastern EA TB Savage 4.4.84 5 20

Search all rows that contain one or more 3

[[email protected] ~]# grep "3\+" Agc.txt

The Soup teaste Good 93

Northwest NW Charles Main 3.0.98 3 34

[Email protected] ~]# egrep "Agc.txt "

The Soup teaste Good 93

Northwest NW Charles Main 3.0.98 3 34

[Email protected] ~]# grep-e "Agc.txt "

The Soup teaste Good 93

Northwest NW Charles Main 3.0.98 3 34

Search for one or more consecutive no rows

[Email protected] ~]# egrep "(NO) +" Agc.txt

Ggnono

Adbcnoinonodd

Northwest NW Charles Main 3.0.. 98 3 34

Football game isn't use feet only.

[Email protected] ~]# grep-e "(NO) +" Agc.txt

Ggnono

Adbcnoinonodd

Northwest NW Charles Main 3.0.. 98 3 34

Football game isn't use feet only.

[[email protected] ~]# grep "\ (no\) \+" Agc.txt

Ggnono

Adbcnoinonodd

Northwest NW Charles Main 3.0.. 98 3 34

Football game isn't use feet only.

Do not use regular expressions

The fgrep query is faster than the grep command , but not flexible enough: it can only find fixed text, not regular expressions.

If you want to find a line that contains an asterisk character in a file or output

[Email protected] ~]# grep-f "*" Agc.txt

9tar**

**ggnono

[Email protected] ~]# fgrep "*" Agc.txt

9tar**

**ggnono

This article is from the "Youth Deng Yong" blog, please be sure to keep this source http://dengyong.blog.51cto.com/8409869/1871005

The grep command is detailed