Linux Learning Record-grep-egrep-is being expressed

Grep

-I ignores case

--color Plus Color

-V shows rows that are not matched to

-O displays only the string that is matched to

Grep-o ROOT/ETC/PASSWD | Wc-l find how many root strings there are

-e Use extended regular expression egrep=grep-e

-A # grep-a 2 ' ^core ID '/proc/cpuinfo

-B # grep-b 2 ' ^core ID '/proc/cpuinfo

-C # grep-c 2 ' ^core ID '/proc/cpuinfo

Regular Expressions: Basic REGEXTP Basics

Extended regextp Extension

Regular expressions

. Represents any single character

* indicates that matches its preceding character any time

(Greedy mode)

AB, AAB, ACB, ADB, AMNB

A*b

A.*b

. * Any character of any length

\? Match the characters in front of it 1 or 0 times

\{m,n\} matches the preceding characters at least m times, up to N times

grep ' A\{1,3\}b ' test.txt

Ab

AaB

grep ' A.\{1,3\}b ' test.txt

Location anchoring:

^ The beginning of the anchor line, the character after the anchor must appear at the beginning of the line

grep ' ^r. T '/etc/passwd

$ Anchor Line end, the character before the anchor must appear at the end of the row

grep ' B. h$ '/etc/passwd

^$ Blank Line

grep ' ^$ '/etc/inittab

\< or \b Anchor Word, any subsequent character must appear as the first word

\> or \b Anchors the ending, any character before it must appear as the tail of the word

\<root\>

Group:

\ (\) to group content

\ (ab\) *

Back to reference

\1 refers to the first opening parenthesis and the corresponding closing parenthesis that contain the contents of the

grep ' \ (1..e\). *\1 ' Test.txt

grep ' \ ([0-9]\). *\1$ '/etc/inittab line appears with numbers that have the same end of data

Extended Regular Expressions: (and general regular expressions differ in many places without adding \)

-e using extended regular expressions

Character Matching:

.

[]

[^]

Number of matches:

*:

?:

+: Match the characters in front of it at least once

？ and + equals *

{M,n}

Group:

()

Or

|

C|cat C or Cat

(C|C) at cat or cat

Linux Learning Record-grep-egrep-is being expressed