Basic usage of regular expressions and grep 9

1. grep: Global RE Printing

Regular Expression

Text filtering tool, which can perform row-by-row search based on the specified pattern)

The content of the file and the matched lines are displayed;

Mode: it is a matching condition consisting of metacharacters of regular expressions and other characters;

RE: Regular Expression

Base RE

Extended RE

Grep [option]... 'pattern' FILE...

-V reverse value;

-- Color = auto-matched characters are displayed in red and bold;

1. Basic Regular Expression metacharacters

.: Match any single character;

For example, grep 'C. U'/proc/cpuinfo;

..: Match 2 characters;

[]: Any single character in the specified range;

For example, grep -- color = auto'c .. [a-z] '/proc/cpuinfo;

[^]: Any character out of the specified range;

2. Times matching greedy match)

*: Match the first character 0, 1 or multiple times;

For example, AB * c: abc, abbc, and ac do not match.) abdc (indicating the appearance of B

Times );

Job (grep.txt file, one of which has the tab key ):

Find AB, a B, accccb;

Grep 'a [[: space:] * B '/tmp/grep.txt;

? : Match the first character 0 or 1 time;

\ {M, n \}: Where \ is conversion, {} is to avoid shell expansion, at least m

N times at most;

\ {M, \}: At least m times;

\ {0, n \}: up to n times;

\ {M \}: m times;

Job:

Exercise the following match:

A [a-z] \ {0, 2 \} c: abc, aaaac, accccc;

3. Anchor

R.. t: root, chroot, rooter;

This is root.

There is chroot.

Word anchoring:

\ <: The beginning of the anchor; for example, \ <r. t;

\>: Specifies the end of a word, for example, root \>;

First line anchored:

^ Escape Character): for example, ^ root;

Anchor at the end of the line:

$: For example, root $;

Job:

A. How to display the rows whose end is root and can contain a punctuation mark;

Grep 'root [[: punct:]? $ 'File = grep' root [[: punct:] \ {0, 1 \} $ 'file;

B. How to display blank rows starting with "root;

Grep '^ [[: space:] * root 'file;

. *: Match any character of any length;

For example, a. * B, a and B can contain any character of any length;

4. Group

Xabababy and AB appear in groups;

\ (\), X \ (AB \) * y

Forward reference:

He love his lover.

She like her liker.

He love his liker.

She like her lover.

L. e. * l.. er;

\ (L. e \). * \ 1r is followed by a number 1 );

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