grep Regular Expression

1. Return to the main knowledge points of this course

chmod, Chown, Umask, grep, Egrep

Rights Management:

Rights Management : chmod

Affiliation Management : Chown, Chgrp

File Matte Code:umask

grep: text Filtering tool;Egrep:grep 's extended version

2.grep Basic Syntax

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

Options:

--color=auto: The matching to the string to do highlighting;

-V: The display mode does not match the row;

-I: ignore character case;

-O: displays only strings that can be matched to the pattern;

-Q: silent mode;

-E: Using extended regular expressions;

The metacharacters of the basic regular expression:

Character Matching:

.: matches any single character;

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

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

[: Lower:], [: Upper:], ...

Number of occurrences: used to specify the number of times after the character;

*: any time;

Abxy

Xay

Xxxxxxxy

grep "X*y"

\? : 0 or 1 times;

grep "X\?y"

\+: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;

. *: matches any character of any length;

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 the word ;

\> \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:

3.display The lines in the /etc/passwd file that end with bash

#grep "bash$"/etc/passwd

4.display the two-digit or three-digit number in the/etc/passwd file

#grep "\<[1-9][0-9]\{1,2\}\>"/etc/passwd

5. Display ' netstat-tan ' command results with ' LISTEN ' followed by 0 ,1 lines ending with one or more whitespace characters

# Netstat-tan |grep-n "\<listen[[:space:]]*$"

6 bash testbash basher nologin user ( nologin user's Span style= "font-family: ' Times New Roman ';" >shell /sbin/ Nologin /etc a row in the /passwd file that has the same user name as its shell name

#useradd bash#useradd testbash#useradd basher#useradd nologin-s/sbin/nologin#grep "^\ (\<[[:alnum:]]\+\>\). *\1 $ "/etc/passwd

8, find A word in the/etc/rc.d/init.d/functions file (the middle of the word can be underlined) followed by a set of parentheses line

grep "\<[[:alnum:]_]\+\> ()"/etc/rc.d/init.d/functions

9, use echo to output a path, and then egrep find its path base name; further use egrep to remove its directory name

#echo/home/mysql/xo/test.sh |grep '. * *

Remove directory name I don't want to write it

Find the number between 1-255 in the ifconfig command Execution result

Ifconfig |grep-e "\< ([1-9]|[ 1-9][0-9]|1[0-9][0-9]|2[0-5][0-5]) \> "

This is the only temporary level that can be written.

grep Regular Expression