Shulou(Shulou.com)06/01 Report--

Need for text lookup:

Grep,egrep,fgrep

Grep: search for text based on the pattern and display lines of text that match the pattern.

Pattern: a matching condition formed by the combination of text characters and metacharacters of regular expressions

Grep [OPTIONS] PATTERN [FILE...]

-I: ignore case

-- color: match highlight color

-v: displays lines that have not been matched

-o: only the strings matched by the pattern are displayed

Regular expressions: GEGular,EXPression,REGEXP

Metacharacters:

.: match any single character

Number of matches:

*: match the characters before them any number of times

[]: matches any single character in the specified range

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

[: digit:], [: lower:], [: upper:], [: punct:], [: space:], [: alpha:], [: alnum:] this is a collection of characters

Add double parentheses when using, for example: [: digit:]

A,b,ab,aab,acb,adb,amnb

Axib

[root@one ~] # grep ahumb test.txt

B

Ab

Aab

Acb

Adb

Amnb

A. Roomb

[root@one ~] # grep 'a.roomb' test.txt

Ab

Aab

Acb

Adb

Amnb

\?: match the character in front of it 1 or 0 times

[root@one] # grep'a\? B 'test.txt

B

Ab

Aab

Acb

Adb

Amnb

\ {mdirection n\}: match the characters before them at least m times and n times at most

\ {1,\} at least once, no limit

\ {0pr 3\} 3 times at most

[root@one ~] # grep'a\ {1Jing 3\} b'test.txt

Ab

Aab

Position Anchor:

^: anchor the beginning of the line, and anything after this character must appear at the beginning of the line

[root@one ~] # grep'^ r.. t'/ etc/passwd

Root:x:0:0:root:/root:/bin/bash

$: anchors the end of the line, and anything before the secondary character must appear at the end of the line

[root@one ~] # grep'b.. hackers'/ etc/passwd

Root:x:0:0:root:/root:/bin/bash

Vagrant:x:500:500:vagrant:/home/vagrant:/bin/bash

Tom:x:501:501::/home/tom:/bin/bash

User3:x:2002:1002:User3,be,110,119:/home/user3:/bin/bash

User4:x:1003:1003:Tony Blare:/home/blare:/bin/bash

User7:x:1006:1006::/home/user7:/bin/bash

Apache:x:497:497::/home/apache:/bin/bash

Hadoop:x:2003:2003::/home/hadoop:/bin/bash

^ $: blank line

Any character in front of it must appear at the end of the word

\ b put before or after a word to indicate an anchor prefix or suffix

Grouping:

\ (\)

\ (ab\) *

Latter item reference

\ 1: reference everything contained in the first left parenthesis and the corresponding closing parenthesis.

\ 2:

\ 3:

He love his lover.

She like her liker.

He like his lover.

[root@one ~] # grep'\ (ab\) * 'test.txt

A

B

Ab

Aab

Acb

Adb

Amnb

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