Linux File Processing tool (grep)

Introduction

grep is a powerful text search tool that uses regular expressions to search for text and print matching lines. The grep full name is global Regular expression Print, which represents the globally regular expression version, and its use rights are for all users.

grep Basic Usage

• Format

grep [options]

• Main parameters

[Options] Main parameters:
-C: Outputs only the count of matching rows.
-I: Case insensitive (only for single-character).
-H: The file name is not displayed when querying multiple files.
-L: Only file names that contain matching characters are output when querying multiple files.
-N: Displays matching lines and line numbers.
-S: does not display error messages that do not exist or have no matching text.
-V: Displays all lines that do not contain matching text.
Pattern Regular Expression Main parameters:
\: Ignores the original meaning of special characters in regular expressions.
^: matches the start line of the regular expression.
$: Matches the end line of the regular expression.
\<: Starts from the line that matches the regular expression.
\>: End of line to match regular expression.
[]: A single character, such as [a], a meets the requirements.
[-]: range, such as [A-z], i.e. A, B, C to Z all meet the requirements.
。 : all the individual characters.
*: There are characters, the length can be 0.

• grep command using exercise (regular expression)

1. Display the line in the/proc/meminfo file that begins with the size S; (Requires: use two ways)

[[email protected] ~]# grep ' ^[ss] '/proc/meminfo

[Email protected] ~]# grep-i ' ^s '/proc/meminfo

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2. Display three user root, Mage, Wang's UID and default shell

[[email protected] ~]# Cat/etc/passwd|egrep "^ (Root|mage|wang) \>" | Cut-d:-f1,3,7

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3. Find the line at the beginning of the/etc/rc.d/init.d/functions file that has a word (including an underscore) followed by a parenthesis [Email protected] ~]# egrep "[_[:alpha:]]+\ (\)"/etc/rc.d/init.d/functions

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4. Use Egrep to remove its base name in/etc/rc.d/init.d/functions

[Email protected] ~]# echo "/etc/rc.d/init.d/functions" | Egrep-o "[^/]+/?$"

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5. Use Egrep to remove the directory name of the path above

[Email protected] ~]# echo "/etc/rc.d/init.d/functions/" | Egrep-o "/.*[^/]" | Egrep-o "/.*/"

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6. Display all IPV4 addresses in ifconfig command results

[Email protected] ~]# Ifconfig | Egrep-o "\< ([0-9]|[ 1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5]) \.) {3} ([0-9]| [1-9] [0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5]) \> "

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Linux File Processing tool (grep)