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This article will explain in detail how to use the grep command in the linux system. The editor thinks it is very practical, so I share it for you as a reference. I hope you can get something after reading this article.

The grep directive is used to find files that contain the specified template style. If the contents of a file are found to match the specified template style, the default grep directive will display the column containing the template style.

Example 1 looks up the pattern (word) in the file

Look for the word "linuxtechi" in the / etc/passwd file

Root@Linux-world:~# grep linuxtechi / etc/passwdlinuxtechi:x:1000:1000:linuxtechi,:/home/linuxtechi:/bin/bashroot@Linux-world:~# example 2 looks for the pattern root@Linux-world:~# grep linuxtechi / etc/passwd / etc/shadow / etc/gshadow / etc/passwd:linuxtechi:x:1000:1000:linuxtechi in multiple files : / home/linuxtechi:/bin/bash / etc/shadow:linuxtechi:$6$ DdgXjxlM$4flz4JRvefvKp0DG6re:16550:0:99999:7:::/etc/gshadow:adm:*::syslog Linuxtechi / etc/gshadow:cdrom:*::linuxtechi / etc/gshadow:sudo:*::linuxtechi / etc/gshadow:dip:*::linuxtechi / etc/gshadow:plugdev:*::linuxtechi / etcGShadowGRAPHART / etc/gshadow:sudo:*::linuxtechi / LPADMIN / EtcUniv / EtcAccording to the file name of the file containing the specified mode, the-L parameter is used to list the filename of the specified mode. : ~ # grep-l linuxtechi / etc/passwd / etc/shadow / etc/fstab / etc/mtab / etc/passwd / etc/shadowroot@Linux-world:~# example 4 uses the-N parameter Find the specified pattern in the file and display the line number of the matching line root@Linux-world:~# grep-n linuxtechi / etc/passwd 39RLINUX techiPart x1000Rd 1000 LINUX techiPhillips LINUX TechiPhones, HomeCome LINUX techiPUBING BHROOTY LinuxLINUX worlds # example 5 Lines using the-V parameter output does not contain the specified pattern

Output all lines in the / etc/passwd file without the word "linuxtechi"

Root@Linux-world:~# grep-v linuxtechi / etc/passwd example 6 use the ^ symbol to output all lines beginning with a specified pattern

The Bash script treats the ^ symbol as a special character and is used to specify the beginning of a line or word. For example, all lines in the output / etc/passes file that start with "root"

Root@Linux-world:~# grep ^ root / etc/passwd root:x:0:0:root:/root:/bin/bashroot@Linux-world:~# example 7 uses the $symbol to output all lines ending in the specified pattern

Output all lines in the / etc/passwd file that end with "bash"

Root@Linux-world:~# grepbash$ / etc/passwd root:x:0:0:root:/root:/bin/bash linuxtechi:x:1000:1000:linuxtechi,:/home/linuxtechi:/bin/bashroot@Linux-world:~#

The Bash script treats the dollar ($) symbol as a special character and is used to specify the end of a line or word.

Example 8 uses the-R parameter to recursively find a specific pattern root@Linux-world:~# grep-r linuxtechi / etc/ / etc/subuid:linuxtechi:100000:65536 / etc/group:adm:x:4:syslog Linuxtechi / etc/group:cdrom:x:24:linuxtechi / etc/group:sudo:x:27:linuxtechi / etc/group:dip:x:30:linuxtechi / etc/group:plugdev:x:46:linuxtechi / etc/group:lpadmin:x:115:linuxtechi / etc/group:linuxtechi:x:1000: / etc/group:sambashare:x:131:linuxtechi / etc/passwd-:linuxtechi:x:1000:1000:linuxtechi : / home/linuxtechi:/bin/bash / etc/passwd:linuxtechi:x:1000:1000:linuxtechi,:/home/linuxtechi:/bin/bash....

The above command will recursively look for the word "linuxtechi" in the / etc directory

Example 9 uses Grep to find all blank lines in the file root@Linux-world:~# grep ^ $/ etc/shadowroot@Linux-world:~#

Since there are no blank lines in the / etc/shadow file, there is no output

Example 10 uses the-I parameter lookup mode

The-I argument of the grep command ignores the case of characters when looking for them. Let's look at an example and look for the word "LinuxTechi" in the paswd file.

Nextstep4it@localhost:~$ grep-I LinuxTechi / etc/passwd linuxtechi:x:1001:1001::/home/linuxtechi:/bin/bashnextstep4it@localhost:~$ example 11 use the-E parameter to find multiple patterns

For example, I want to look for the words' linuxtechi' and 'root' in a grep command, and using the-e parameter, we can find multiple patterns

Root@Linux-world:~# grep-e "linuxtechi"-e "root" / etc/passwd root:x:0:0:root:/root:/bin/bash linuxtechi:x:1000:1000:linuxtechi,:/home/linuxtechi:/bin/bashroot@Linux-world:~# example 12 use-F files to specify the mode to be found

First, create a search pattern file "grep_pattern" in the current directory. I want the following input in the file

Root@Linux-world:~# cat grep_pattern ^ linuxtechi root false$root@Linux-world:~#

Now, try using the grep_pattern file to search

Root@Linux-world:~# grep-f grep_pattern / etc/passwd example 13 uses the-C parameter to calculate the number of pattern matches

Continuing with the example above, we use the-c command in the grep command to calculate the number of matches to the specified pattern

Root@Linux-world:~# grep-c-f grep_pattern / etc/passwd 22root@Linux-world:~# example 14 output matches the N lines before or after the specified pattern line

A) use the-B parameter to output the first four lines of the matching line

Root@Linux-world:~# grep-B 4 "games" / etc/passwd

B) use the-A parameter to output the last 4 lines of the matching line

Root@Linux-world:~# grep-A 4 "games" / etc/passwd

C) use the-C parameter to output 4 rows before and after matching lines

Root@Linux-world:~# grep-C 4 "games" / etc/passwd on "how to use grep commands in linux system" this article is shared here, I hope the above content can be of some help to you, so that you can learn more knowledge, if you think the article is good, please share it out for more people to see.

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