The egrep of the Linux base regular expression

First, the basic regular expression

• A regular expression is a pattern written by a class of special characters and text characters, some of which do not represent the literal meaning of a character, but are a function of control or wildcard that supports grep, SED, awk, vim;
• Regular expression is a kind of grammatical rule used to describe character arrangement and matching pattern, which is mainly used for the operation of pattern segmentation, matching and finding substitution of string.
• GREP-V Reverse Search

-I ignores case

-n Displays matching line numbers

-C Statistics match the number of rows without displaying search results

-O displays only the characters that match

-Q does not display results

(1)^: match with what begins---^ab to match lines that begin with AB;

(2)$: matches the line with what ends---ab$ represents a line that matches the end of AB;

(3)^$: match blank line---means match blank line, do not match space;

(4). : matches any single character---ab. Indicates that the match is ABC or ABC, does not match ABCD or ABCE, including spaces

(5)\: escape character, escape the special symbol------A\.B represents the line that matches the A.B, the actual property of the escape point, and does not represent any character;

(6)*: match the preceding item 0 or more times---ab* means match a or AB or B or ABB, as long as one or more lines match the AB character;

(7). *: matches any character---ab.* means match ab or either ABC or ABD, including spaces;

(8)[]: matches any single character within the set---AB[CD] means match ABC or ABC, does not match Abe or ABF;

(9)[^]: matches any single character other than the set---AB[^CD] b means match Abe or ABF, does not match abc,abd;

1. Expression test Data

[email protected]/]# cat test
I am Oldboy Teacher!
Iteach Linux.

I like Badminton Ball,billard Ball and Chinese chess.

My blog is http//:oldboy.blog.51cto.com
Our site is http://www.etiantian.org

My QQ num is 49000048

Not 4900000048
My god,i am not oldbey,but Oldboy

Oldb y

(1) ^: match with what begins

[[email protected]/]# grep "^m" test
My blog is http//:oldboy.blog.51cto.com
My QQ num is 49000048
My god,i am not oldbey,but Oldboy

(2) $: match the line with what ends

[[email protected]/]# grep "m$" test
My blog is http//:oldboy.blog.51cto.com

(3) ^$: Match blank line (use-VN parameter to troubleshoot blank lines, show only non-blank lines)

[Email protected]/]# grep-vn "^$" test
1:i am Oldboy Teacher!
2:iteach Linux.
5:i like Badminton Ball,billard Ball and Chinese chess.
7:my Blog is http//:oldboy.blog.51cto.com
8:our site is http://www.etiantian.org
12:my QQ num is 49000048
15:not 4900000048
16:my god,i am not oldbey,but Oldboy
18:oldb y

(4). : Matches any single character

[[email protected]/]# grep "M." Test
I am Oldboy Teacher!
I like Badminton Ball,billard Ball and Chinese chess.
My blog is http//:oldboy.blog.51cto.com
My QQ num is 49000048
My god,i am not oldbey,but Oldboy

(5) \: Escape character, escape special symbol

[Email protected]/]# grep "\.$" Test #以点结尾的行
Iteach Linux.
I like Badminton Ball,billard Ball and Chinese chess.

(6) *: Matches the previous item 0 or more times

[Email protected]/]# grep-o "0*" Test #精确匹配显示匹配的数据
0000
000000

(7). *: Matches any character

[[email protected]/]# grep ". *" Test all matches, including spaces
I am Oldboy Teacher!
Iteach Linux.

I like Badminton Ball,billard Ball and Chinese chess.

My blog is http//:oldboy.blog.51cto.com
Our site is http://www.etiantian.org

My QQ num is 49000048

Not 4900000048
My god,i am not oldbey,but Oldboy

Oldb y

(8) []: matches any single character within the set

[[email protected]/]# grep "[0-9]" test #匹配有数字的行
My blog is http//:oldboy.blog.51cto.com
My QQ num is 49000048
Not 4900000048

(9) [^]: matches any single character other than the set

[[email protected]/]# grep "[^0-9]" test #匹配非数字的行;
I am Oldboy Teacher!
Iteach Linux.
I like Badminton Ball,billard Ball and Chinese chess.
My blog is http//:oldboy.blog.51cto.com
Our site is http://www.etiantian.org
My QQ num is 49000048
Not 4900000048
My god,i am not oldbey,but Oldboy
Oldb y

Second, extended regular expression

Test data

[email protected] ~]# cat Test1
I am Oldboy Teacher!
Iteach Linux.

I like Badminton Ball,billard Ball and Chinese chess.

My blog is http//:oldboy.blog.51cto.com
Our site is http://www.etiantian.org

My QQ num is 49000048

Not 4900000048
My god,i am not oldbey,but Oldboy

Good
Goood

Gd

(1) +: match the previous 1 or more---ab+ indicates a match AB or ABB, does not match A;

[Email protected] ~]# grep-e "Go+d" test1
My god,i am not oldbey,but Oldboy
Good
Goood

(2)? : Match the previous 0 or 1 times---ab? Indicates matching A or AB, does not match ABB;

[Email protected] ~]# grep-e "Go?d" test1
My god,i am not oldbey,but Oldboy
Gd

(3) | : Match any of the---ab|cd to match ab or CD;

[Email protected] ~]# grep-e "God|good" test1
My god,i am not oldbey,but Oldboy
Good

(4) (): Match Expression---A (CD) e indicates matching Ace or ADE, does not match AE;

[[email protected] ~]# grep-e "G (a|oo) d" test1
Good

[Email protected] ~]# grep-e "G (OO) d" test1
Good
Gd

(5) {n,m}: Matches the previous item n~m times---ab{2,3} indicates matching ABB or ABBB, and {} needs to be escaped;

[[email protected] ~]# grep-e "0{3,5}" test1
My QQ num is 49000048
Not 4900000048

(6) {n,}: matches the preceding item at least n times, contains n times---ab{2,} indicates matching ABB or ABBB, need to escape {};

[Email protected] ~]# grep-e "0{3,}" test1
My QQ num is 49000048
Not 4900000048

(7) {n}: matches the preceding item n times---ab{2} matches ABB, need to escape {};

[[email protected] ~]# grep-e "O{1}" test1
My god,i am not oldbey,but Oldboy

(8) {, m}: matches the preceding item up to M times, contains m times,---ab{,2} matches a or AB or ABB, need to escape {};

The egrep of the Linux base regular expression