Linux_egrep and extended Regular expressions

05_01_egrep and extended Regular expressions

Regular expressions are divided into two categories:

Basic REGEXP: base Regular Expression

Extended REGXP: extending regular Expressions

grep: A command to filter text using a template defined by a basic regular expression

- e: using extended regular expressions, grep-e = Egrep

- A number: When grep matches, the next number of rows ( the number of rows is the number after a) is immediately displayed.

- b numbers: ..... ..... Front..............

- c number: ..... ..... Before and after ......

An extended regular expression:

Character Matching:

Same as the basic regular expression

. Single character

[] in-range characters

[^] out of range characters

Number of matches:

*: The first 0 or any time. Is the same as the basic regular expression.

？ : the first 0 or 1 times. The basic regular expression needs to be preceded by the addition of \, the extension does not need to add.

+: Match its first character at least once

{M,n} does not require \:

Positional anchoring is the same as the basic regular expression.

Group:

(): Group, do not need \

\1,\2,\3 ...

Or

|: Indicates or a|b represents a or B ... c|cat: denotes C or cat, (C|C) at: Indicates cat or cat

650) this.width=650; "src=" Http://s3.51cto.com/wyfs02/M00/72/6E/wKioL1Xj8YyBuPbyAABPMQanKko108.jpg "title=" 3cbb4811-3cf7-400b-afa0-da97fb38e1be.jpg "alt=" Wkiol1xj8yybupbyaabpmqankko108.jpg "/>

The number of 1-9, or 10-99, or 100-199, or 200-249, or 250-255.

Fgrep: Regular expressions are not supported, but fast

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Linux_egrep and extended Regular expressions