Linux egrep file content search tool and extended regular expression detailed

Linux egrep file content search tool and extended regular expression detailed

egrep Command : Search for text based on patterns (matching criteria for text characters and extended Regular expression meta-character combinations)

and displays the line of text that conforms to the pattern.

Format: egrep [option] Match condition text name

egrep equals Grep-e .

Option:-I: Ignore case

-V: Show rows that are not matched by the pattern

-O: Displays only strings that are matched by the pattern

--color: Search out files High brightness display

-A: Matches the next few lines of the specified line

-B: Matches the last few rows of the specified row

-C: matches the upper and lower lines of the specified row

Regular Expressions : Regular expression, abbreviated RegExp

Meta characters :

.: Matches any single character

[]: matches any single character within the specified range

[^]: matches any single character outside the specified range

For example: special character set: [:d igit:], [: Lower:], [: Upper:], [:p UNCT:], [: Space:], [: Alpha:], [: Alnum:]

number of matches :

*: Matches any of its preceding characters any time

. *: Any character of any length

?: matches the preceding character 1 or 0 times, not like a basic regular expression, without adding \

{a,d}: matches the preceding character at least a, at most d times, not like a basic regular expression, without adding \

For example: {1} indicates that the preceding character matches 1 times

{0,6} means: The preceding character matches at least 0 times, up to 6 times

The position is locked or called anchored :

^: Locks the beginning of the line, any content after this character must appear at the beginning of the line

Example: Displaying lines beginning with R in the/etc/passwd file

egrep ' ^r '/etc/passwd

$: Locks the end of the line, any content that precedes this character must appear at the end of the row

Example: Show the line in the/etc/passwd file that the bash ends

egrep ' bash$ '/etc/passwd

^$: Indicates a blank line

\< or \b: Anchor word, any character following it must appear as the first word

\> or \b: anchors the ending, any character preceding it must appear as the tail of the word

Example: Displays a line in the/etc/passwd file that begins with Root and ends with the root word

egrep ' ^root\> '/etc/passwd

grouping : () is not like a basic regular expression, without adding \

For example: (MN) * indicates matching any MN combination character

Back to reference

\1: Refers to the first opening parenthesis and all the contents of the corresponding closing parenthesis

\2: Refers to the second opening parenthesis and all the contents of the corresponding closing parenthesis

\ n: references the nth opening parenthesis and all the contents of the corresponding closing parenthesis

or : |

To illustrate:

1.d|dog represents D and dog, not dog and dog.

2. Find the number between 1-255 in the/boot/grub/grub.conf file

Egrep--color ' \< ([1-9]|[ 1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5]) \> '/boot/grub/grub.conf

650) this.width=650; "src=" Http://s5.51cto.com/wyfs02/M01/7E/E8/wKiom1cMheHjDdXWAAG85_y-2OA660.jpg "title=" Egrep1.jpg "alt=" Wkiom1cmhehjddxwaag85_y-2oa660.jpg "/> 3. Find the IP address in the ifconfig command: Again,egrep equals grep-e

Ifconfig | grep--color-e ' (\< ([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]) \> '

650) this.width=650; "src=" Http://s1.51cto.com/wyfs02/M01/7E/E5/wKioL1cMh_azzWHJAAGNRTnZvvI126.jpg "title=" Egrep2.jpg "alt=" Wkiol1cmh_azzwhjaagnrtnzvvi126.jpg "/>

This article is from the "Xavier Willow" blog, please be sure to keep this source http://willow.blog.51cto.com/6574604/1762934

Linux egrep file content search tool and extended regular expression detailed