Use regular expressions and grep

I. Regular Expressions

Regular Expression mode: greedy mode, non-Greedy Mode

Regular Expressions include basic regular expressions and extended regular expressions.

1. Basic Regular Expression

^	Specifies the content at the beginning of a line, such as ^ pattern.
$	Anchor specifies the content at the end of a line, for example, pattern $
^ $	Blank line
.	Match any single character
*	Match any character on the left
.*	Match any character of any length
[]	Match any single character in the specified range
[^]	Matches any single character out of the specified range
\?	Match 0 or 1 character on the left
\ {M, n \}	Match the character on the left at least m times, at most n times
\ {M ,\}	Match at least m characters on the left
\ {M \}	Match the exact m characters on the left
\ <	The beginning of the anchor, for example, \ <pattern
\>	Pin the end of a word, for example, pattern \>
\ <\>	Anchoring a word is not an English word in the true sense), \ <pattern \>
\ B	Character boundary, similar to the \ <, \> function, such as: \ bpattern \ B anchored word)
\ (Pattern \)	Group, for example, \ (abc \). * \ 1 Description: here 1 represents 1st groups

[: Lower:]	Lowercase letters
[: Upper:]	Uppercase/lowercase letters
[: Digit:]	Number
[: Alpha:]	Letter
[: Alnum:]	Letters and numbers
[: Space:]	Space
[: Punct:]	Letters other than letters, numbers, controls, and blank spaces)

2. Extended Regular Expressions

+	Repeat one or more previous characters
?	Zero or one previous character
|	Or, select one more
()	Group
() +	Repeat one or more previous Groups
{M, n}	Match the character on the left at least m times, at most n times
\ <\>	Pin words

It also includes all basic regular expressions. Except \ <and \>, backlash is not required in extended regular expressions.

For more regular expressions, see man 7 regex.

Can also refer to: http://www.cnblogs.com/lcf/articles/807523.html

Ii. Use grep

Grep supports basic regular expressions.

Egrep supports extension of the regular expression equivalent to: grep-E)

Fgrep does not support pattern matching, but it is fast

Command: grep

Purpose: print the row matching the pattern.

Parameters:

-- Color = auto	The matched information is marked with colors. The auto option can be omitted. Modify the default color scheme (foreground and background): export GREP_COLOR = '01; 36'
-V	Reflection Selection
-O	Only the strings matched by the pattern are displayed.
-I	Case Insensitive
-W	Match words
-R	Recursive search
-#	Displays the matched rows and the # Rows following them.
-B #	Show the matched rows and the # Rows in front of them
-C #	Displays the matched rows and the # Rows before and after the matched rows.
-E	Use extended Regular Expressions

Iii. Example:

Matched IP Address:

Ifconfig | egrep -- color "([1-9] | [1-9] [0-9] | 1 [0-9] {1} | 2 [0-4] [0-9] | 25 [0-5]) \. ([0-9] | [1-9] [0-9] | 1 [0-9] [0-9] | 2 [0-4] [0-9- 9] | 25 [0-5]) \.) {2} ([1-9] | [1-9] [0-9] | 1 [0-9] {1} | 2 [0-4] [0- 9] | 25 [0-5])"

Iv. Notes

1. grep basic regular expression) in use, the indicator must be added with a backslash (\), while the egrep extension Regular Expression) but cannot be added with a backslash \:

Grep -- color "\ (error \)"*

Egrep -- color "(error )"*

Egrep -- color "\ <(error)" * \ <, \>: Except for word anchoring)

This article from the "Linux/Unix O & M Technology" blog, please be sure to keep this source http://wangyc.blog.51cto.com/31193/1304976