Linux Regular expressions

Regular Expressions:

also called conventional notation. Regular expressions are described using a single string, matching a series of strings that conform to a given sentence plan, and regular expressions are often used to retrieve and replace text that conforms to a pattern.

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1. Grep:

   The grep command in a Linux system is a powerful text search tool that can use regular expressions to search for text and print matching lines, using permissions for all users.

Use format: grep [option]

Main parameters:[option]

-C: Output only the number of rows matching rows

-I: Case insensitive (only for single-character)

-H: Do not display file names when querying multiple files

-L: Only file names with matching characters are output when querying multiple files

-N: Display matching lines and line numbers

-S: Do not display error messages for nonexistent or no matching text

-V: Displays all lines that do not include matching text

Pattern Regular Expression Main parameters:

\: Ignores the original meaning of special characters in regular expressions

^: match the start line of the regular expression

$: Match the end line of a regular expression

\<: Starting with the line that matches the regular expression

\>: End of line to match regular expression

[]: A single character, such as [a] that a meets the requirements

[-]: range, e.g. [A-z], i.e. a,b,c until Z meets requirements

。 : All the individual characters

*: With characters, length can be 0

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The number of rows with the ' root ' character in the output/etc/passwd file, which is 2

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Outputs all rows with ' root ' characters in the/etc/passwd file, and displays the number of rows per line, divided into 1, 11

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Displays all lines in the/etc/passwd file that do not contain the ' HUNGSS ' character

Displays all lines in the/etc/shadow file that do not contain the ' root ' character

This article is from the "Not So Simple" blog, be sure to keep this source http://hungss5657.blog.51cto.com/8011603/1439758