The application of-grep and regular expressions in the learning path of Linux

The application of grep and regular expressions

Linux Text Processing Three musketeers:

grep: text filtering tools;

sed : Text editor (line); stream Editor

awk : Text report Generator; awk implementation on Linux is Gawk

grep : Global search REgular expression and Print out Theline.

Function: Text Search tool, according to user-specified "pattern" line to search for target text, print the matching line;

pattern : The filter condition written by metacharacters and text characters of regular expressions;

grep [OPTIONS] PATTERN [FILE ...] :

Options:

--color=auto : The matching string is highlighted;

- v : Displays the lines that the pattern does not match;

- I.: ignores character case;

- o: display only the string lines that can be matched to the pattern, and each match to a row, you can easily count the number of times;

- Q: silent mode;

- e : Using an extended regular expression;

The basic regular expression is divided into 2 categories:

Basic Regular Expressions: BRE

Extended Regular expression: ERE

Metacharacters of the basic Regular expression: (character does not represent its literal meaning, but is used to denote a wildcard or control function)

character matching:

                .: match any single character;

[]: matches any single character within the specified range;

                [^] : matches any single character within the specified range;

[: Lower:],[:upper:], ...

number of matches: used to specify the number of times the character behind, can only be used for the previous character;

                *: any time;

Abxy

Xay

Xxxxxxxy

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                \? : 0 or 1 times;

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                \+ : 1 or more times;

\{m\} : Precisely limited to M times;

\{m,n\}: at least m times, up to n times, [M,n]

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

\{m,\} : at least m times;

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                .*: match any character of any length;

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Location anchoring:

                ^: anchor at the beginning of the line, for the leftmost mode;

                $: end of line anchoring; for the rightmost side of the pattern;

\<,\b: The first anchor of the word; the left side of the pattern used to denote words;

\>,\b : the ending anchor; the right side of the pattern used to represent the word;

                ^$: blank line;

Group: \ (\)

The contents of the pattern in the grouped parentheses are recorded by the regular expression engine during execution, and the built-in variables are saved: The variables are \1, \2, ...

\ 1: from the left, the first opening parenthesis, and the matching right parenthesis in the middle of the pattern match to the content;

\2 :

...

Back reference: Use a variable to refer to the character that matches the pattern in the preceding grouping brackets;

This article is from the "naïve Little Comrade" blog, please be sure to keep this source http://dengxi.blog.51cto.com/4804263/1689496

The application of-grep and regular expressions in the learning path of Linux