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This article mainly introduces how to use grep, sed and awk in Shell regular expressions. It has certain reference value. Interested friends can refer to it. I hope you will gain a lot after reading this article. Let Xiaobian take you to understand it together.

First, copy an example:

The code is as follows:

# vi regular_express.txt

-------------------------------

"Open Source" is a good mechanism to develop programs.

apple is my favorite food.

Football game is not use feet only.

this dress doesn't fit me.

However, this dress is about $ 3183 dollars.

GNU is free air not free beer.

Her hair is very beauty.

I can't finish the test.

Oh! The soup taste good.

motorcycle is cheap than car.

This window is clear.

the symbol '*' is represented as start.

Oh! My god!

The gd software is a library for drafting programs.

You are the best is mean you are the no. 1.

The world is the same with "glad".

I like dog.

google is the best tools for search keyword.

goooooogle yes!

go! go! Let's go.

# I am VBird

--------------------------------

Set the language family to C

The code is as follows:

#export LANG=C

grep

1. Search for specific string "the"

Note: n is the display line number

The code is as follows:

# grep -n 'the' regular_express.txt

2. Reverse search for specific string "the"

The code is as follows:

# grep -vn 'the' regular_express.txt

3. Get this string with any case of "the"

The code is as follows:

# grep -in 'the' regular_express.txt

4. Use brackets [] to search for set characters

When searching for the words test or taste, you find that they have a common't? st', so you can search like this

The code is as follows:

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

So what we're looking for is t[a]st and t[e]st, two separate characters.

If you are searching for characters with oo, you can use:

The code is as follows:

# grep -n 'oo' regular_express.txt

If we don't want to find a g before oo when searching oo, we can use reverse selection [^] to achieve:

The code is as follows:

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

If you don't want lowercase characters before the search oo, then:

The code is as follows:

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

Note: Upper/Lower case English/Numbers can be written in [a-z]/[A-Z]/[0-9], etc., or can be written together

[a-zA-Z0-9] indicates that the required string is numeric and English

If we want to get the row with numbers, then:

The code is as follows:

# grep -n '[0-9]' regular_express.txt

Note: However, considering the influence of language families on coding order, in addition to using minus [-] for continuous coding,[:lower:] can also be used instead of a-z and [:digit:] can be used instead of 0-9.

The code is as follows:

# grep -n '[^[:lower:]]oo' regular_express.txt

# grep -n '[[:digit:]]' regular_express.txt

5. Display strings starting with 'the'

The code is as follows:

# grep -n '^the' regular_express.txt

Display lines begin with lowercase characters

The code is as follows:

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

6. Display line ends with dots. the line that

The code is as follows:

# grep -n '\.$ ' regular_express.txt

7. Display 5-9 rows of data

The code is as follows:

# cat -An regular_express.txt |head -n 10 |tail -n 6

8. Display blank lines

The code is as follows:

# grep -n '^$' regular_express.txt

9. Find out g d string, four strings starting with g and ending with d

The code is as follows:

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

10. o* stands for empty characters (that is, with or without characters) or one to N o characters, so grep -n 'o*' regular_express.txt will print out all lines,

11.oo* stands for o+ null characters or one to N o characters, so grep -n 'oo*' regular_express.txt will print out all the lines o,oo,ooo, etc.

12. "goo*g" stands for gog,goog,gooog... such

The code is as follows:

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

13. Find out what contains g... g line of string

Note: Represents any character, .* then it represents a null character or one to N arbitrary characters.

The code is as follows:

# grep -n 'g.* g' regular_express.txt

14. Find the rows that contain numbers

The code is as follows:

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

or # grep -n '[0-9]' regular_express.txt

15. Find a string with two o's

Note:{} Because it has a special meaning in the shell, it needs to add the escape character\to make it meaningless.

The code is as follows:

# grep -n 'o\{2\}' regular_express.txt

Find a string with 2 to 5 o's after g and ending with g

The code is as follows:

# grep -n 'go\{2,5\}g' regular_express.txt

Find a string with an o after g and then ending in g

The code is as follows:

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

Summary:

^word indicates string with search (word) at the beginning of the line

word$indicates the string with search (word) at the end of the line

. Represents 1 arbitrary character

\means escape character, adding\before special character will remove the original special character meaning

* Represents repeating 0 to an infinite number of previous RE(regular expression) characters

[list] means to search for strings containing lists

[n1-n2] means to search the specified string range, for example,[0-9] [a-z] [A-Z], etc.

[^list] indicates a range of inverted strings, e.g.[0-9] for non-numeric characters,[A-Z] for non-upper case character ranges

\{n,m\} means find n to m previous RE characters

\{n,\} indicates more than n previous RE characters

egrep Summary:

+ Indicates repetition of one or more previous RE characters

Example:egrep 'go+d' regular_express.txt

indicates search for (god)(good)(goood)... string, o+ stands for [more than one o]

? Indicates a repeat of zero or one previous RE character

Example:egrep 'go? d' regular_express.txt

The search for (gd)(god) string, o? stands for [blank or 1 o]

Note: 'go+d' and 'go' under egrep? the result set of d'is equal to'go*d'under grep

| Indicates finding several strings by or (or)

Example:egrep 'gd| good| dog' regular_express.txt

indicates search for (gd) or (god) or (god) strings,| representative or

() means find group string

Example:egrep 'g(la| oo)d' regular_express.txt

indicates a search (glad) or (good) string

() + indicates identification of multiple duplicate groups

Example: echo 'AxyzC'| egrep 'A(xyz)+C'

Indicates that the search starts with A and ends with C, with more than one 'xyz' string in between.

sed:

Insert:

1. List the contents of/etc/passwd and print the line numbers. At the same time, delete lines 2-5 and display them.

The code is as follows:

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

Note: sed is short for sed -e, followed by single quotation marks

Ibid. Delete line 2

The code is as follows:

# nl /etc/passwd | sed '2d'

Same as above Delete third line to last line

The code is as follows:

# nl /etc/passwd | sed '3,$d'

2. Add a test line after the second line

The code is as follows:

# nl /etc/passwd | sed '2a test'

Add a test line before the second line

The code is as follows:

# nl /etc/passwd | sed '2i test'

Add two lines of test after the second line

The code is as follows:

# nl /etc/passwd | sed '2a test \

> test'

Replace line:

3. Replace lines 2-5 with No 2-5 number

The code is as follows:

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

4 List lines 5-7 in/etc/passwd

The code is as follows:

# nl /etc/passwd |sed -n '5,7p'

Replacement string:

sed 's/substituted string/new string/g'

1. Get the line of native IP

The code is as follows:

# /sbin/ifconfig eth0 |grep 'inet addr'

Delete the first part of IP

The code is as follows:

# /sbin/ifconfig eth0 |grep 'inet addr'| sed 's/^.* addr://g'

Delete the part after IP

The code is as follows:

# /sbin/ifconfig eth0 |grep 'inet addr'| sed 's/^.* addr://g'| sed 's/Bcast:.*$// g'

-------------------

192.168.100.74

-------------------

2. Use grep to extract the keyword MAN from the row

The code is as follows:

# cat /etc/man.config |grep 'MAN'

Delete comment line

The code is as follows:

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

Delete blank rows

The code is as follows:

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

3. Use sed to convert each line in regular_express.txt to. Change it!

Note: The-i parameter modifies text directly, not output directly

The code is as follows:

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

4.#This is a test

Note: $stands for the last line and a stands for adding after the line

The code is as follows:

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

Change the selinux profile enforcing to disabled

The code is as follows:

# sed -i '6,6c SELINUX=disabled' /etc/selinux/config

Extended normal notation:

The code is as follows:

# grep -v '^$' regular_express.txt |grep -v '^#'

Extended Writing:

The code is as follows:

# egrep -v '^$'|'^#' regular_express.txt

1. + indicates repetition of one or more previous RE characters

egrep -n 'go+d' regular_express.txt

Common spelling: grep -n 'goo*d' regular_express.txt

2. ? Indicates repetition of zero or one previous RE character

For example: egrep -n 'go? d' regular_express.txt

3. |Indicates to find several strings using or

For example: egrep -n 'gd| good' regular_express.txt

4. () means find group string

egrep -n 'g(la)| oo)d' regular_express.txt

which is to search for the two strings glad or good.

5. ()+ Multiple repeat group discrimination

For example: echo 'AxyzC'| egrep 'A(xyz)+C'

That is to say, it is necessary to find the meaning of the string that starts with A and ends with C and has more than one 'xyz' character in the middle.

awk:

1. Use last to extract the first five lines of landing data

The code is as follows:

# last -n 5

Take out the account and login IP, and the account and IP are separated by TAB.

The code is as follows:

# last -n 5 |awk '{print $1 "\t" $3}'

Note:$1 represents the first field separated by a space or TAB, and so on.

$0 represents all fields in the row

The code is as follows:

# last -n 5 |awk '{print $1 "\t lines:" NR "\t columes:" NF}'

Note: NF stands for the total number of fields per line for $0

NR represents the line number of data awk is currently in.

FS stands for target delimiter, default is space

2. In/etc/passwd with: as a segmentation character, we have to look up the third column less than 10 data, and only list the account number and the third column

The code is as follows:

# cat /etc/passwd | awk '{FS=":"} $3

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