Grep and Regular Expression

Grep [acivn] [-- color = auto] 'query string' filename

-A: query the data of binary files as text files.

-C: calculates the number of times a 'query string' is found.

-I: case insensitive

-V: Reverse Selection

-N: list the row numbers of the search results.

-- Color = Auto: keyword coloring in search results

* ********* Grep example **********

(1) list the names of directories in a directory:

Ll | grep '^ d' | awk' {print $9 }'

In awk, $ is followed by the column position.

(2) list an object and remove blank lines:

Grep-V '^ $'/etc/httpd/CONF/httpd. conf

(3) Remove comment lines

Grep-V '^ $'/etc/httpd/CONF/httpd. conf | grep-V '^ #'

(4) Ignore the case and indicate the row number:

Dmesg | grep-in 'network'

(5) Search for a word that starts with M and ends with M.

Grep-In'm [A-Z] * m' regular_express.txt

* ********* Regular Expression basics **********

-- Word string

-- Char character

-- List Character Sequence

^ Word indicates that it starts with word

Word $ indicates ending with word

. Indicates that there must be an arbitrary character.

Char * Indicates zero or Infinitely multiple repeated char

\ Escape characters

[LIST] indicates selecting a character match. For example, a [BC] A indicates ABA & ACA

[Char1-char2] represents any consecutive character, char1 to char2, for example [A-Z] represents any lowercase letter

[^ List] indicates removing unwanted characters and indicates reverse selection. For example, [^ ABC] indicates removing rows containing ABC strings.

Char \ {n, m \} indicates n to M Char. escape characters are required.

Eg: a script to simulate service httpd status output

#!/bin/bash#The output of commond "service httpd status" or "/etc/init.d/httpd status"m=$(ps -ef |grep httpd |sed ‘s/^.*grep.*$//g‘ |sed ‘/^$/d‘)n=$(ps -ef |grep httpd |sed ‘s/^.*grep.*$//g‘ |sed ‘/^$/d‘ |grep root |grep /usr/sbin/httpd |awk ‘{print $2}‘)#n=$(ps -ef |grep httpd |grep -v grep |grep root |grep /usr/sbin/httpd |awk ‘{print $2}‘)#n=$(ps -ef |grep httpd |sed ‘/.*grep.*/d‘ |grep root |grep /usr/sbin/httpd |awk ‘{print $2}‘)if [ "$m" = "" ];then        echo "httpd is stopped"else        echo "httpd (pid  "$n") is running..."fi

This article from the "Little cainiao" blog, please be sure to keep this source http://akiny09.blog.51cto.com/1299657/1429980