grep, egrep and corresponding regular expression usage

Regular Expressions (REGGXP):

A regular expression is a filtering logic (that is, a pattern) of a string. is a pattern written by metacharacters and normal characters, in which the metacharacters do not represent the meaning of the character itself, but are used to express control or to function as a wildcard, and can be divided into two types:

1. Basic Regular Expressions

2. Extending the regular expression

Grep:

A text Search tool to complete text filtering based on basic regular expressions

Egrep

A text Search tool to complete text filtering based on extended regular expressions

Regular Expressions Common meta-character meanings :

Listing 1: For basic regular expressions

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Listing 2: For extended regular expressions

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Note: the patterns in the grouping, the characters that are matched during a specific match, can be memorized by grep (stored in the built-in variables, these variables are \1,\2,... ), so that it can also be referenced

\1: Reference, from left to right in a pattern, matched by the first opening parenthesis and the pattern in the right parenthesis corresponding to it

\2: Reference, from left to right in a pattern, matched by the second opening parenthesis and the pattern in the right parenthesis corresponding to it

grep:

The Text Search tool searches the target file on a per-line basis according to the user-specified text pattern and displays the rows that can be matched to.

Use format:

grep [OPTIONS] PATTERN [FILE ...]

                     --color[=when],--colour[=when]        &NBSP,                

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-O: Displays only the content that is matched by the pattern;                    

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-i:ignore case, character case insensitive;

-V: Displays rows that cannot be matched to the pattern;

-E: Using extended regular expressions;

-A #: Displays the number of rows specified after matching rows;

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-B #: Displays the number of rows specified before matching the line;

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-C #: Displays the number of rows specified before and after the matching line;

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Egrep:

Use format:

Egrep [OPTIONS] PATTERN [FILE ...]

This article is from "Just like the Beginning" blog, please be sure to keep this source http://10066605.blog.51cto.com/10056605/1629046

grep, egrep and corresponding regular expression usage