grep text-processing tool, regular expression

grep is a text retrieval tool, known as one of the Three Musketeers of Linux text processing, usually combined with regular expressions, support basic regular expressions and extended regular expressions, the function is very powerful, to our search text brought great convenience, by default, it is greedy mode, can match how long to match how long, The entire line that matches to is displayed. The other two great musketeers: sed, awk.

grep Common options:

Grep-i: Ignoring case

[email protected] ~]# grep-i tom/etc/passwd

Tom:x:506:506::/home/tom:/bin/bash

Tom:x:507:507::/home/tom:/bin/bash

Grep-o: Show only the text that matches to

[email protected] ~]# Grep-o root/etc/passwd

Root

Root

grep --color: Highlighting matched text

[Email protected] ~]# grep--color=auto tom/etc/passwd

Tom: x:506:506::/home/Tom:/bin/bash

grep-v: Display text other than matching text

[Email protected] ~]# grep-v tom/etc/passwd |tail-2

Named:x:25:25:named:/var/named:/sbin/nologin

Tom:x:507:507::/home/tom:/bin/bash

GREP-E: Represents a logical relationship "or"

[Email protected] ~]# grep-e tom-e tom/etc/passwd

Tom:x:506:506::/home/tom:/bin/bash

Tom:x:507:507::/home/tom:/bin/bash

Grep-q: Silent mode, no match to or not matched to text display

[Email protected] ~]# grep-q tom/etc/passwd

[Email protected] ~]#

grep-a #: Display mode matches to the text and displays after # lines

[Email protected] ~]# grep-a 1 named/etc/passwd

Named:x:25:25:named:/var/named:/sbin/nologin

Tom:x:506:506::/home/tom:/bin/bash

Grep-b #: Display pattern matches to the text and displays the front # lines

[Email protected] ~]# Grep-b 1 named/etc/passwd

Mage:x:505:505::/home/mage:/bin/bash

Named:x:25:25:named:/var/named:/sbin/nologin

Grep-c #: Displays the text to which the pattern matches, and displays the front and back # lines

[Email protected] ~]# grep-c 1 named/etc/passwd

Mage:x:505:505::/home/mage:/bin/bash

Named:x:25:25:named:/var/named:/sbin/nologin

Tom:x:506:506::/home/tom:/bin/bash

GREP-E: Support for extended regular expressions

grep is based on pattern matching, which supports basic regular expressions by default and supports extended regular expressions using the-e option, equivalent to Egrep.

Regular expressions have a number of meta-characters, with the basic regular expression Bre and the extended regular expression ere.

Basic regular Expression meta-character: BRE

Character Matching:

.: Matches any single character

"": matches any single character in the range

"^": match any single character outside the range TT

":d igit:"::: All Numbers ": Alnum:": All numbers and letters

": Lower:": All lowercase letters ": space:": white space characters

":p UNCT:": All Punctuation ": Alpha:": All Letters

": Upper:": All uppercase letters

[[email protected] ~]# grep t.m/etc/passwd

Tom:x:507:507::/home/tom:/bin/bash

[[email protected] ~]# grep [Tt]/etc/passwd |tail-2

Tom:x:506:506::/home/tom:/bin/bash

Tom:x:507:507::/home/tom:/bin/bash

number of matches:

*: matches the preceding character any time

. *: Matches any character of any length

\+: Matches the preceding character at least once

\？ : matches the preceding character 0 or 1 times

\{m\}: Matches the preceding character m times

\{m,n\}: Matches the preceding character at least m times, up to N times

\{m,\}: Matches the preceding character at least m times

\{,n\}: Matches the preceding character up to n times

[[email protected] ~]# grep "X*y" Hadop

Xxy

Xy

YY matches the previous x any time, 0 times also matches

[[email protected] ~]# grep "X\+y" Hadop

Xxy

XY matches the previous X at least once

[[email protected] ~]# grep "X\{2\}y" Hadop

XXY matches the previous x two times, exact match

Location Anchoring:

^: Anchor at the beginning of the line

$: End of line anchoring

^$: Blank Line

^pattern$: For pattern matching entire row

^*$: Non-blank line

\< or \b: The first anchor of the word

\> or \b: Final anchoring

\<pattern\>: Anchoring the whole word

[[email protected] ~]# grep "^root"--color=auto/etc/passwd

Root:x:0:0:root:/root:/bin/bash

[[email protected] ~]# grep "/sbin/nologin$"/etc/passwd |head-2

Bin:x:1:1:bin:/bin:/sbin/nologin

Daemon:x:2:2:daemon:/sbin:/sbin/nologin

Group:

\ (\): One or more characters are bundled together and treated as a whole, and the contents of the grouping match are recorded in the internal variables by the regular expression engine, which are named: \1,\2,\3 .... You can make a back reference that references the character that the pattern in the preceding grouping matches to

\1: From the left, the first opening parenthesis and the character matching the pattern between the closing parenthesis.

\ (string1\+\ (string2\) *\)

\1:string1\+\ (string2\) *

\2:string2

[[email protected] ~]# grep "\ (r. t\). *\1 "--color=auto/etc/passwd

Root:x:0:0:root:/root:/bin/bash

The previous match to Root, recorded in the variable \1, after the reference, in the bank, in the presence of root will be pattern matching

[[email protected] ~]# grep "\ (r. t\) "--color=auto/etc/passwd

Root:x:0:0:root:/root:/bin/bash

Operator:x:11:0:operator:/root:/sbin/nologin

Ftp:x:14:50:ftp user:/var/ftp:/sbin/nologin

If you only group, do not make a back reference, the result is so, as long as the group matching to will show

extended Regular Expression meta-character: ERE

Extended regular expression metacharacters are more concise than basic regular expressions, character matching, positional anchoring, and meta-characters are the same. Only the number of times matches and the grouping meta characters are slightly biased.

Number of matches:

*: matches the preceding character any time

. *{}: Matches any character of any length

+: Match the preceding character at least once

？ : matches the preceding character 0 or 1 times

{m}: Matches the preceding character m times

{M,n}: matches the preceding character at least m times, up to N times

{, n}: matches the preceding character up to n times

{m,}: matches the preceding character at least m times

Group: ()

This article is from the "Linux" blog, so be sure to keep this source http://wei2008.blog.51cto.com/11351016/1795388

grep text-processing tool, regular expression