Linux Basic Text Search tool grep

One, grep (abbreviated from globally search a Regular expression and print) is a powerful text-search tool that can use regular expressions to search for text and print matching lines. The grep family of Unix includes grep, egrep, and Fgrep

grep: The default support for basic regular expressions;
Egrep: extended regular expression;
Fgrep: Regular expression metacharacters are not supported, fast searching for strings

Second, get grep help information through the man manual:

#man grep

grep (1) grep (1)

NAME
grep, Egrep, fgrep-print lines matching a pattern

Synopsis
grep [Options] PATTERN [FILE ...]
grep [Options] [-E PATTERN |-f file] [FILE ...]

DESCRIPTION
Grep searches the named input FILEs (or standard input if no FILEs is named, or the file Name-is given) for
Lines containing a match to the given PATTERN. By default, grep prints the matching lines.

In addition, the variant programs Egrep and Fgrep are available.   Egrep is the same as GREP-E. Fgrep is the
Same as Grep-f.

Iii. Common options for grep

--color=auto
Export grep_color= ' 01;36 '
-V: Reverse selection, showing only rows that do not conform to the pattern;
-O: Displays only strings that are matched to the pattern, not the entire row;
-I: case-insensitive character;
-A #: Displays the row to which it was matched, showing the # lines following it, incidentally;
-A 2
-B #: line in front of #;
-C #: Before and after the # line;

-E: Using extended regular expressions
GREP-E = Egrep

C. grep regular expression basic meta-character set

Metacharacters: does not represent the meaning of the character itself, but is used for the description of the additional functionality

^: Qualifying content anchored at the beginning of the line

# grep "^root"/etc/passwd//search for lines starting with root

650) this.width=650; "title=" image "style=" border-left-0px; border-right-width:0px; Background-image:none; border-bottom-width:0px; padding-top:0px; padding-left:0px; margin:0px; padding-right:0px; border-top-width:0px "border=" 0 "alt=" image "src=" http://s3.51cto.com/wyfs02/M02/59/FF/ Wkiom1tx8mageib7aacumwhbtoi608.jpg "width=" 430 "height=" "/>"
$: Anchoring line endings for eligible content

#grep "bash$"/etc/passwd//search for lines ending in bash

650) this.width=650; "title=" image "style=" border-left-0px; border-right-width:0px; Background-image:none; border-bottom-width:0px; padding-top:0px; padding-left:0px; margin:0px; padding-right:0px; border-top-width:0px "border=" 0 "alt=" image "src=" http://s3.51cto.com/wyfs02/M00/59/FF/wKiom1Tx8mahtvRKAAFlzLFIJ_ Y687.jpg "width=" 718 "height=" 113 "/>

.: Matches any single character

650) this.width=650; "title=" image "style=" border-left-0px; border-right-width:0px; Background-image:none; border-bottom-width:0px; padding-top:0px; padding-left:0px; margin:0px; padding-right:0px; border-top-width:0px "border=" 0 "alt=" image "src=" http://s3.51cto.com/wyfs02/M01/59/FF/ Wkiom1tx8mejsljqaabjwdukhlm862.jpg "width=" 407 "height=" 118 "/>

Matches the contents of a single arbitrary character between S and L

650) this.width=650; "title=" image "style=" border-left-0px; border-right-width:0px; Background-image:none; border-bottom-width:0px; padding-top:0px; padding-left:0px; margin:0px; padding-right:0px; border-top-width:0px "border=" 0 "alt=" image "src=" http://s3.51cto.com/wyfs02/M02/59/FF/ Wkiom1tx8meizfo3aaa0w1mq3k8100.jpg "width=" 382 "height="/>

*: matches the character immediately preceding it any time (contains 0 times)

650) this.width=650; "title=" image "style=" border-left-0px; border-right-width:0px; Background-image:none; border-bottom-width:0px; padding-top:0px; padding-left:0px; margin:0px; padding-right:0px; border-top-width:0px "border=" 0 "alt=" image "src=" http://s3.51cto.com/wyfs02/M00/59/FF/ Wkiom1tx8mfjzppraaa197kztko611.jpg "width=" "height=" 104 "/>

Match k with 0 or any s in front of

650) this.width=650; "title=" image "style=" border-left-0px; border-right-width:0px; Background-image:none; border-bottom-width:0px; padding-top:0px; padding-left:0px; margin:0px; padding-right:0px; border-top-width:0px "border=" 0 "alt=" image "src=" http://s3.51cto.com/wyfs02/M01/59/FF/wKiom1Tx8mfSMIZ0AAA8EBIf_ 1a788.jpg "width=" 383 "height=" "/>

[]: matches any single character within the specified range

Match D or D in the middle of a line containing two arbitrary characters and ending with n

650) this.width=650; "title=" image "style=" border-left-0px; border-right-width:0px; Background-image:none; border-bottom-width:0px; padding-top:0px; padding-left:0px; padding-right:0px; border-top-width:0px "border=" 0 "alt=" image "src=" http://s3.51cto.com/wyfs02/M00/59/FC/ Wkiol1tx83ehuwyjaagtfx1iaow409.jpg "width=" 973 "height="/>
[^]: matches any single character outside the specified range

650) this.width=650; "title=" image "style=" border-top:0px; border-right:0px; Background-image:none; border-bottom:0px; padding-top:0px; padding-left:0px; margin:0px; border-left:0px; padding-right:0px "border=" 0 "alt=" image "src=" http://s3.51cto.com/wyfs02/M00/59/FC/ Wkiol1tx83fieyeyaabqimqkh60087.jpg "" 327 "height="/>

#grep "[^a-z].*a" text--color=auto//matches any one of the lines that is not large with the letter followed by 0 or more arbitrary characters ending with a

650) this.width=650; "title=" image "style=" border-top:0px; border-right:0px; Background-image:none; border-bottom:0px; padding-top:0px; padding-left:0px; margin:0px; border-left:0px; padding-right:0px "border=" 0 "alt=" image "src=" http://s3.51cto.com/wyfs02/M01/59/FC/ Wkiol1tx83etu7moaab1x9qnmr0819.jpg "" 572 "height=" "/>
\?: matches the character immediately preceding it 0 or 1 times;

0 or 1 a before matching B

650) this.width=650; "title=" image "style=" border-top:0px; border-right:0px; Background-image:none; border-bottom:0px; padding-top:0px; padding-left:0px; border-left:0px; padding-right:0px "border=" 0 "alt=" image "src=" http://s3.51cto.com/wyfs02/M02/59/FC/ Wkiol1tx83jyobxcaactuglycai155.jpg "" 619 "height=" 224 "/>

There are 0 or 1 arbitrary characters before matching A and b

650) this.width=650; "title=" image "style=" border-top:0px; border-right:0px; Background-image:none; border-bottom:0px; padding-top:0px; padding-left:0px; border-left:0px; padding-right:0px "border=" 0 "alt=" image "src=" http://s3.51cto.com/wyfs02/M00/59/FC/ Wkiol1tx83iwjlroaabdehnpqwu846.jpg "" 630 "height=" 104 "/>

\{m,n\}: Matches its preceding character at least m times, up to n times;
\{0,n\}: Up to n times; 0-n times;
\{m,\}: At least m times
\{m\}: Exact match m times;

Match A in front of b at least 1 times up to 2 times

650) this.width=650; "title=" image "style=" border-top:0px; border-right:0px; Background-image:none; border-bottom:0px; padding-top:0px; padding-left:0px; margin:0px; border-left:0px; padding-right:0px "border=" 0 "alt=" image "src=" http://s3.51cto.com/wyfs02/M01/59/FC/ Wkiol1tx83irjstbaacecvyhbk0574.jpg "" 571 "height=" 225 "/>

\<: Anchor word First, usage format: \<pattern
\b: \bpattern

Search for lines with root as the first word

650) this.width=650; "title=" image "style=" border-top:0px; border-right:0px; Background-image:none; border-bottom:0px; padding-top:0px; padding-left:0px; margin:0px; border-left:0px; padding-right:0px "border=" 0 "alt=" image "src=" http://s3.51cto.com/wyfs02/M01/5A/00/ Wkiom1tx8mqqhweuaadfxi3ysyw567.jpg "" 618 "height=" "The/>

\>: Anchor ending, usage format:pattern\>
\b:pattern\b

Search for a line ending in root

650) this.width=650; "title=" image "style=" border-top:0px; border-right:0px; Background-image:none; border-bottom:0px; padding-top:0px; padding-left:0px; margin:0px; border-left:0px; padding-right:0px "border=" 0 "alt=" image "src=" http://s3.51cto.com/wyfs02/M02/5A/00/ Wkiom1tx8mqgan89aaduvhvpps8557.jpg "" 591 "height="/>
\<pattern\>: Anchoring words

Search for lines that contain root words

650) this.width=650; "title=" image "style=" border-top:0px; border-right:0px; Background-image:none; border-bottom:0px; padding-top:0px; padding-left:0px; margin:0px; border-left:0px; padding-right:0px "border=" 0 "alt=" image "src=" http://s3.51cto.com/wyfs02/M00/5A/00/ Wkiom1tx8mrspid1aacxsqgcvj8824.jpg "" 626 "height="/>

\ (\): Group, usage format: \ (pattern\)

\1: You can refer to what the first grouping matches
\2: You can refer to what the second grouping matches

Search for two arbitrary characters between R or R and D followed by 0 or more arbitrary characters, followed by references to matched content

650) this.width=650; "title=" image "style=" border-top:0px; border-right:0px; Background-image:none; border-bottom:0px; padding-top:0px; padding-left:0px; margin:0px; border-left:0px; padding-right:0px "border=" 0 "alt=" image "src=" http://s3.51cto.com/wyfs02/M01/5A/00/ Wkiom1tx8muzkupraaeefs66li4136.jpg "" 626 "height=" 138 "/>

Character Set fit

[:d igit:] All numbers 0-9

[: Lower:] All lowercase letters A-Z

[: Upper:] All capital letters A-Z

[:p UNCT:] All punctuation

[: Space:] Indicates a space or TAB key

[: Alpha:] denotes all letters (including capitalization) a-za-z

[: Alnum:] denotes all letters and numbers a-za-z0-9

Note: It is not necessary to represent [^[]], such as [[: space:]] means space [^[:space:]] means non-empty

Search/boot/grub/grub.conf lines that begin with a space

650) this.width=650; "title=" image "style=" border-top:0px; border-right:0px; Background-image:none; border-bottom:0px; padding-top:0px; padding-left:0px; margin:0px; border-left:0px; padding-right:0px "border=" 0 "alt=" image "src=" http://s3.51cto.com/wyfs02/M01/59/FC/ Wkiol1tx83rwoucgaac8mozxyrg269.jpg "" 685 "height="/>

Linux Basic Text Search tool grep