-12,grep regular expressions and extended regular expressions for Linux basic articles

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Basic Regular Expressions: Grep uses patterns defined by regular expressions to filter text

Grep

-I: Case insensitive

--color

-V: Displays any rows that are not matched

-O: Show only strings that are matched

The-e extension is exactly the expression =egerp

-a#: #为数字

-b#:

-c#:

[[email protected] testcp]# grep-o ' root '/etc/passwd--color

Root

Root

Root

Root

Metacharacters

.: Matches any single character

[]: matches a single character within a specified range

[^]: matches any single character outside the specified range

Number of matches:

*: matches the preceding character any time

. *: Matches any string

\? Match the preceding character 1 or 0 times

\{m,n\}: Matches the preceding character m-n times

Location Anchorage

^: Anchoring the beginning of the line

\< or \b: Any character after the first anchor word must appear as a word header

\<root

$: Anchor Line End

\> or \b: Any character in front of the anchor ending appears as a word in the tail

Root\>

\ (abc\) as content occurrence and extended regular expression similarity

Support for back-to-reference

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Extended Regular expression: REGular expression regexp

Metacharacters

.: Matches any single character

[]: matches a single character within a specified range

[^]: matches any single character outside the specified range

Number of matches:

*: matches the preceding character any time

. *: Matches any character

\? Match the preceding character 1 or 0 times

+: Match the preceding character at least 1 times

{M,n}: match the preceding character

[Email protected] ~]# Cat/tmp/t.txt

It is open no opening

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Location Anchorage

^: Anchoring the beginning of the line

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$: Anchor Line End

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^$: Blank Line

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\< or \b: Any character after the first anchor word must appear as a word header

\<root

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\> or \b: Any character in front of the anchor ending appears as a word in the tail

Root\>

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(AB) * Grouping (usually expanded with parentheses as the word appears)

[[email protected] ~]# grep ' (ABC) * '-e--color/tmp/t.txt

Ab

Abc

AaB

Aaac

Support for back reference \1,\2

[[email protected] ~]# grep-e ' (open). *\1 '/tmp/t.txt--color

It is open no opening

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|: OR OR

Write 1-255 in full expression

\<[1-9]| [1-9] [0-9]|1[0-9][0-99]|2[0-4][0-9]|25[0-5]\>

Filter out numbers between 0-255 in the NIC configuration file

Ifconfig | Grep-e ' (\<[0-9]|[ 1-9][0-9]|1[0-9][0-99]|2[0-4][0-9]|25[0-5]\>) '--color

[Email protected] ~]# CAT/ETC/PASSWD | grep ' nologin\> '--color

Bin:x:1:1:bin:/bin:/sbin/nologin

Daemon:x:2:2:daemon:/sbin:/sbin/nologin

Adm:x:3:4:adm:/var/adm:/sbin/nologin

Lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin

Mail:x:8:12:mail:/var/spool/mail:/sbin/nologin

Uucp:x:10:14:uucp:/var/spool/uucp:/sbin/nologin

This article is from the "James Zhan Linux Advanced ops" blog, so be sure to keep this source http://jameszhan.blog.51cto.com/10980469/1875541

-12,grep regular expressions and extended regular expressions for Linux basic articles