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This article mainly introduces "the use of grep and fgrep commands in the Linux system". In the daily operation, I believe that many people have doubts about the use of grep and fgrep commands in the Linux system. The editor consulted all kinds of materials and sorted out simple and easy-to-use operation methods. I hope it will be helpful to answer the doubts about the use of grep and fgrep commands in the Linux system. Next, please follow the editor to study!

Grep

Grep (global search regular _ expression (RE) and print out the line, full search for regular expressions and printing lines) is a powerful text search tool that uses regular expressions to search for text and print matching lines. Unix's grep family includes grep, egrep and fgrep. The commands of egrep and fgrep are only slightly different from grep. Egrep is an extension of grep to support more re metacharacters. Fgrep is fixed grep or fast grep, which treats all letters as words, that is, metacharacters in regular expressions express their own literal meaning and are no longer special. Linux uses the GNU version of grep. It is more powerful, and you can use the functions of egrep and fgrep through the-G,-E,-F command line options.

Grep works like this by searching for string templates in one or more files. If the template includes spaces, it must be referenced, and all strings after the template are treated as file names. The results of the search are sent to the screen without affecting the contents of the original file.

Grep can be used for shell scripts because grep returns a status value to indicate the status of the search, 0 if the template search is successful, 1 if the search is unsuccessful, and 2 if the searched file does not exist. We can use these return values to do some automated text processing.

Grep-help

Match pattern selection:

-E,-- extended-regexp extends the regular expression egrep

-F,-- fixed-strings a collection of newline delimited strings fgrep

-G,-- basic-regexp basic regular

-P,-- perl regularity of perl-regexp call

-e,-- regexp=PATTERN follows the root regular mode. Default is none.

-f,-- file=FILE gets the matching pattern from the file

-I,-- ignore-case is case-insensitive

-w,-- word-regexp matches the whole word

-x,-- line-regexp matches the whole line

-z,-- null-data a row of 0 bytes of data, but not a blank line

Miscellaneous:

-s,-- no-messages does not display error messages

-v,-- invert-match displays mismatched lines

-V,-- version displays the version number

-- help displays help information

-- mmap use memory-mapped input if possible

Input control:

-m,-- the maximum number of max-count=NUM matches

-b,-- byte-offset prints the block number in front of the matching line.

-n,-- line-number display plus the line number where the match is located

-- line-buffered refreshes each line of output

-H,-- with-filename displays matching file name prefixes when searching for multiple files

-h,-- no-filename does not show matching file name prefixes when searching for multiple files

-- label=LABEL print LABEL as filename for standard input

-o,-- only-matching displays only those parts of a line that match PATTERN

-Q,-- quiet,-- silent doesn't show anything.

-- binary-files=TYPE assumes the TYPE type of the binary file

TYPE can be `binary', `text', or `without-match'

-a,-- text matches something binary.

-I don't match the binary.

-d,-- directories=ACTION directory operation, read, recursion, skip

-D,-- devices=ACTION sets operations on devices, FIFO, pipes, reads, skips

-R,-r,-- recursive recursive call

-- include=PATTERN only looks for files that match FILE_PATTERN

-- exclude=PATTERN skips files and directories that match FILE_PATTERN

-- exclude-from=FILE skips all files except FILE

-L,-- files-without-match displays mismatched file names when multiple files are matched

-l,-- files-with-matches displays matching file names when multiple files are matched

-c,-- count shows how many matches have been made.

-Z,-- null prints empty characters at the end of the FILE file

File control:

-B,-- before-context=NUM print matching itself and the first few lines are controlled by NUM

-A,-- after-context=NUM print matching itself and subsequent lines are controlled by NUM

-C,-- context=NUM print the match itself and then the first few lines are controlled by NUM

-NUM root-C is used the same way

-- color [= WHEN]

-- colour [= WHEN] uses flags to highlight matching strings

-U,-- binary uses flags to highlight matching strings

-u,-- unix-byte-offsets when the CR character does not exist, report byte offset (MSDOS mode)

Example:

Test file

The code is as follows:

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

Bin:x:1:1:bin:/bin:/bin/false,aaa,bbbb,cccc,aaaaaa

DADddd:x:2:2:daemon:/sbin:/bin/false

Mail:x:8:12:mail:/var/spool/mail:/bin/false

Ftp:x:14:11:ftp:/home/ftp:/bin/false

& nobody:$:99:99:nobody:/:/bin/false

Zhangy:x:1000:100:,:/home/zhangy:/bin/bash

Http:x:33:33::/srv/http:/bin/false

Dbus:x:81:81:System message bus:/:/bin/false

Hal:x:82:82:HAL daemon:/:/bin/false

Mysql:x:89:89::/var/lib/mysql:/bin/false

Aaa:x:1001:1001::/home/aaa:/bin/bash

Ba:x:1002:1002::/home/zhangy:/bin/bash

Test:x:1003:1003::/home/test:/bin/bash

@ zhangying:*:1004:1004::/home/test:/bin/bash

Policykit:x:102:1005:Po

A, matching the row with root

The code is as follows:

[root@krlcgcms01 test] # grep root test

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

B, match lines that begin with root or zhang, pay attention to the backslash

The code is as follows:

[root@krlcgcms01 test] # cat test | grep'^\ (root\ | zhang\)'

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

Zhangy:x:1000:100:,:/home/zhangy:/bin/bash

C, match lines that start with root or zhang, pay attention to the backslash, as in the previous example,-e is omitted by default

[root@krlcgcms01 test] # cat test | grep-e'^\ (root\ | zhang\)'

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

Zhangy:x:1000:100:,:/home/zhangy:/bin/bash

D, the match starts with zhang and contains only letters

The code is as follows:

[root@krlcgcms01 test] # echo 'zhangying' | grep' ^ zhang [amerz] * $'

Zhangying

E, matches the line that starts with bin, using egrep, which can be replaced here with-Fjormer G

The code is as follows:

[root@krlcgcms01 test] # cat test | grep-E'^ bin'

Bin:x:1:1:bin:/bin:/bin/false,aaa,bbbb,cccc,aaaaaa

F, precede the matching line with the line number in the file, or the line number in the output

The code is as follows:

[root@krlcgcms01 test] # cat test | grep-n zhangy

7:zhangy:x:1000:100:,:/home/zhangy:/bin/bash

13:ba:x:1002:1002::/home/zhangy:/bin/bash

15:@zhangying:*:1004:1004::/home/test:/bin/bash

G, does not match lines that begin with bin, and displays line numbers

The code is as follows:

[root@krlcgcms01 test] # cat test | grep-nv'^ bin'

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

DADddd:x:2:2:daemon:/sbin:/bin/false

Mail:x:8:12:mail:/var/spool/mail:/bin/false

Ftp:x:14:11:ftp:/home/ftp:/bin/false

& nobody:$:99:99:nobody:/:/bin/false

Zhangy:x:1000:100:,:/home/zhangy:/bin/bash

Http:x:33:33::/srv/http:/bin/false

Dbus:x:81:81:System message bus:/:/bin/false

Hal:x:82:82:HAL daemon:/:/bin/false

Mysql:x:89:89::/var/lib/mysql:/bin/false

Aaa:x:1001:1001::/home/aaa:/bin/bash

Ba:x:1002:1002::/home/zhangy:/bin/bash

Test:x:1003:1003::/home/test:/bin/bash

@ zhangying:*:1004:1004::/home/test:/bin/bash

Policykit:x:102:1005:Po

H, displays the number of matches, but does not display the content

The code is as follows:

[root@krlcgcms01 test] # cat test | grep-c zhang

three

I, match system, no plus-I, no match.

The code is as follows:

[root@krlcgcms01 test] # grep system test

[root@krlcgcms01 test] # grep-ni system test

9:dbus:x:81:81:System message bus:/:/bin/false

J, matching zhan does not match anything, matching zhangy can match, because in the test file, there is the word zhangy

The code is as follows:

[root@krlcgcms01 test] # cat test | grep-w zhan

[root@krlcgcms01 test] # cat test | grep-w zhangy

Zhangy:x:1000:100:,:/home/zhangy:/bin/bash

Ba:x:1002:1002::/home/zhangy:/bin/bash

K, which is output only when the thing after-x is the same as the whole line in the output.

[root@krlcgcms01 test] # echo "aaaaaa" | grep-x aaa

[root@krlcgcms01 test] # echo "aaaa" | grep-x aaaa

Aaaa

L, only match once at most. If-M1 is removed, there will be three.

The code is as follows:

[root@krlcgcms01 test] # cat test | grep-m 1 zhang

Zhangy:x:1000:100:,:/home/zhangy:/bin/bash

M, the block number is shown in front of the matching line. What is this block number for? I don't know. Who knows if you can tell me?

The code is as follows:

[apacheuser@krlcgcms01 test] $cat test | grep-b zha

241:zhangy:x:1000:100:,:/home/zhangy:/bin/bash

480:ba:x:1002:1002::/home/zhangy:/bin/bash

558:@zhangying:*:1004:1004::/home/test:/bin/bash

N, when multiple files match, add the file name before the matching line

The code is as follows:

[apacheuser@krlcgcms01 test] $grep-H 'root' test test2 testbak

Test:root:x:0:0:root:/root:/bin/bash

Test2:root

Testbak:root:x:0:0:root:/root:/bin/bash

O, when multiple files match, do not precede the matching line with the file name

The code is as follows:

[apacheuser@krlcgcms01 test] $grep-h 'root' test test2 testbak

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

Root

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

P, when multiple files match, the file name of the matching file is displayed

The code is as follows:

[apacheuser@krlcgcms01 test] $grep-l 'root' test test2 testbak DAta

Test

Test2

Testbak

Q, when there is no-o, there is a line that matches. There are three root in this line. After adding-o, the three root come out.

The code is as follows:

[apacheuser@krlcgcms01 test] $grep 'root' test

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

[apacheuser@krlcgcms01 test] $grep-o 'root' test

Root

Root

Root

R, recursively display the matching content, create a mytest directory under the test directory, and go the test file under the copy test directory to the mytest, and you can see the above result.

The code is as follows:

[root@krlcgcms01 test] # grep test-R / tmp/test/mytest

/ tmp/test/mytest/test:test:x:1003:1003::/home/test:/bin/bash

/ tmp/test/mytest/test:@zhangying:*:1004:1004::/home/test:/bin/bash

S, showing the 3 lines after matching root

The code is as follows:

[root@krlcgcms01 test] # cat test | grep-A 3 root

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

Bin:x:1:1:bin:/bin:/bin/false,aaa,bbbb,cccc,aaaaaa

Daemon:x:2:2:daemon:/sbin:/bin/false

Mail:x:8:12:mail:/var/spool/mail:/bin/false

Fgrep

Usage: fgrep [option]. PATTERN [FILE]...

Look for PATTERN in each FILE or standard input.

PATTERN is a set of fixed-length strings separated by line breakers.

For example: fgrep-I 'hello world' menu.h main.c

Regular expression selection and interpretation:

-e,-- regexp=PATTERN uses PATTERN for matching operation

-f,-- file=FILE gets PATTERN from FILE

-I,-- ignore-case ignores case

-w,-- word-regexp forces PATTERN to only exactly match words

-x,-- line-regexp forces PATTERN to match only one row exactly

-z,-- null-data a row of 0 bytes of data, but not a blank line

Miscellaneous:

-s,-- no-messages does not display error messages

-v,-- invert-match selects mismatched rows

-V,-- version displays version information and exits

-- help displays this help and exits

-- mmap ignores backward compatibility

Output control:

-m,-- the maximum number of max-count=NUM matches

-b,-- byte-offset prints the block number in front of the matching line

-n,-- line-number display plus the line number where the match is located

-- line-buffered refreshes each line of output

-H,-- with-filename displays matching file name prefixes when searching for multiple files

-h,-- no-filename does not show matching file name prefixes when searching for multiple files

-- label=LABEL use LABEL as the standard input file name prefix

-o,-- only-matching displays only those parts of a line that match PATTERN

-Q,-- quiet,-- silent does not display all output

-- binary-files=TYPE assumes the TYPE type of the binary file

TYPE can be `binary', `text', or `without-match'

-a,-- text is equivalent to-- binary-files=text

-I equals-- binary-files=without-match

-d,-- the way directories=ACTION operates the directory

ACTION can be `read', `recurse', or `skip'

-D,-- devices=ACTION operating device, first-in, first-out queue, socket mode

ACTION can be `read' or `skip'

-R,-r,-- recursive is equivalent to-- directories=recurse

-- include=FILE_PATTERN only looks for files that match FILE_PATTERN

-- exclude=FILE_PATTERN skips files and directories that match FILE_PATTERN

-- exclude-from=FILE skips all files except FILE

-- exclude-dir=PATTERN skips all directories that match PATTERN.

-L,-- files-without-match prints only file names that do not match FILEs

-l,-- files-with-matches prints only file names that match FILES

-c,-- count prints only the number of matching lines in each FILE

-T,-- initial-tab line header tabs separation (if necessary)

-Z,-- null prints empty characters at the end of the FILE file

File control:

-B,-- before-context=NUM prints NUM lines that start with text

-A,-- after-context=NUM prints NUM lines that end with text

-C,-- context=NUM printout text NUM line

-NUM is equivalent to-- context=NUM

-- color [= WHEN]

-- colour [= WHEN] uses flags to highlight matching strings

WHEN can be `always', `never' or `auto'

-U,-- binary do not clear the CR character at the end of the line (MSDOS mode)

-u,-- unix-byte-offsets when the CR character does not exist, report byte offset (MSDOS mode)

Fgrep' is no longer in use; please use 'grep-F' instead.

Standard input will be read without the FILE parameter, or if FILE is -. If less than two FILE parameters

The-h parameter is used by default. If any row is selected, the exit status is 0, otherwise it is 1

If an error occurs and the-Q parameter is not specified, the exit status is 2.

Example:

The code is as follows:

[root@linux test] # cat abc.sh | fgrep a # matches the line containing a

At this point, the study on the use of grep and fgrep commands in the Linux system is over. I hope to be able to solve your doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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