Basic usage of Grep,egrep regular expressions in Linux

Regular expressions

I wrote the blog for the first time. The basic use of regular expressions has just been learned recently. Organized, and later used to review the search.

The basic description of regular expressions:

Basically, a regular expression is a pattern used to describe a certain amount of text, and the shorthand for regular expressions is the Regex full name regular Express.

The first regular expression is very important for Linux OPS engineers, which will accompany every operational engineer's career. Speaking of regular expressions so have to say grep and Egrep,grep full name is globally search for a Regular expression and print out of the line, the global search regular expression and print the meaning of matching results, good Now let's uncover the mystery of regular expressions together.

Common formats:

grep [option] "pattern" FILE

Common options:

--color indicates that the matching result is displayed in highlight color

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-I: Indicates case insensitive

. : (decimal point) means any single character that matches any

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-V: Indicates everything except the displayed result (without the-V effect above)

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-O: Indicates that only matching content is displayed

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*: Indicates the character before the match any time

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. *: Indicates any character that matches any length

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-N is a number that shows the matched content and the n rows following it

Example:

-a 1, such as:

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-B N: = n is a number, showing the match to the content and the rows preceding it

Example:

-B 1, such as:

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-C-N is a number, showing the matched content and its n rows

Example:

-C 1, such as:

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Regular expression meta-characters:

^: Indicates the beginning of the anchor, format:

' ^pattern '

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$: Indicates the beginning of the anchor, format:

' pattern$ '

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Note: Special usage, matching whitespace behavior ' ^$ '

[]: Indicates any character in the match range

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[^]: Indicates any single content outside of the matching range

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Common Range Representation format:

[0-9]: means all numbers equal to [[:d Igit:]]

[A-Z]: Indicates that all lowercase letters are equal to [[: Lower:]]

[A-Z]: Indicates that all uppercase letters are equivalent to [[: Upper:]]

[A-za-z]: Indicates that all letters are equal to [[: Alpha:]]

[a-za-z0-9]: means that letters and numbers are equal to [[: Alnum:]]

[[: Graph:]]: denotes non-null characters (non-spaces, control characters)

[[: Cntrl:]]: Indicates control character

[[:p UNCT:]]: denotes punctuation

[[:p Rint:]]: Indicates non-null characters (including spaces)

[[: Space:]]: denotes whitespace characters

\? : Indicates a match before the character 0 or 1 times

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\{m,n\}: Indicates that the character before the match is at least m times, up to N times

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\{0,n\}: Indicates that the character before the match is up to N times

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\{m,\}: Indicates that the character before the match is at least n times

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\{m\}: Indicates that the character before the match is at least m times

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\<: Indicates the first anchor of the word, the same as the use of \b

\>: Indicates the word ending anchor, equivalent to the use of \b

such as:\<word\>: The anchor word, the equivalent of \bword\b personally feel \b easier haha

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Grouping and referencing:

\ (pattern\): Represents the character to which this PATTERN is matched as an inviolable whole

\ (pattern\). *\1: Indicates references to previously grouped content

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Egrep Meta-characters:

+: Indicates that the preceding character matches at least once

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| : The pipe character is represented here | on either side of the symbol

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( | ) : With parentheses

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？ : Equal to \ in grep?

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(): equivalent to \ (\) in grep

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{}: Equivalent to grep in \{\}

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Case:

1. Show rows in Test.txt that do not end in CB

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2. Locate the three-bit or four-digit number in the test file

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3. Locate the/etc/grub2.cfg file, starting with at least one whitespace character followed by a non-whitespace character line;

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4. Find the result of "fdisk-l" command, including the line with/dev/followed by SD or HD and a small letter;

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This article is from the Linux OPS blog, so be sure to keep this source http://lailai900201.blog.51cto.com/3094187/1750221

Basic usage of Grep,egrep regular expressions in Linux