Example of a 14 grep command

Overview:

All Linux-class systems provide a search tool called grep (Global Regular expression print, which is the output of globally regular expressions). The grep command is useful in situations where a pattern-based search is performed on the contents of one or more files. A pattern can be a single character, multiple characters, a single word, or a sentence.

When the command matches the pattern specified when the command is executed, grep outputs a line containing the pattern, but does not modify the contents of the original file.

In this article, we will discuss 14 examples of GREP commands.

Example 1 finding a pattern in a file (word)

Find the word "Linuxtechi" in the/etc/passwd file

Root@Linux-World:~/etc/passwdlinuxtechi:x:+: : Linuxtechi,,,:/Home/Linuxtechi:/bin/bashroot @Linux -World:~#

Example 2 finds a pattern in multiple files.

Root@Linux-World~# grep Linuxtechi/etc/passwd/etc/Shadow/etc/Gshadow/etc/PASSWD:LINUXTECHI:X: +: +: Linuxtechi,,,:/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/etc/Gshadow:lpadmin:!::linuxtechi/etc/gshadow:linuxtechi:!::/etc/Gshadow:sambashare:!::linuxtechiroot@Linux-World~#

Example 3 uses the-l parameter to list the file name of the file that contains the specified pattern.

[Email protected]:~# grep-l Linuxtechi/etc/passwd/etc/shadow/etc/fstab/etc/mtab/etc/passwd/etc/shadow[email protected]:~#

Example 4 uses the-n parameter to find the specified pattern in the file and displays the line number of the matching row

[Email protected]:~# grep-n Linuxtechi/etc/passwd39:linuxtechi:x:1000:1000:linuxtechi,,,:/home/linuxtechi:/bin/ Bash[email protected]:~#

[Email protected]:~# grep-n Root/etc/passwd/etc/shadow

Example 5 using the-v parameter to output rows that do not contain a specified pattern

Output all lines in the/etc/passwd file that do not contain the word "Linuxtechi"

R[email protected]:~# grep-v linuxtechi/etc/passwd

Example 6 using the ^ symbol to output all lines beginning with a specified pattern

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

[Email protected]:~# grep ^root/etc/passwdroot:x:0:0:root:/root:/bin/bash[email protected]:~#

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".

[Email protected]:~# grep bash$/etc/passwdroot:x:0:0:root:/root:/bin/bashlinuxtechi:x:1000:1000:linuxtechi,,,:/ Home/linuxtechi:/bin/bash[email protected]:~#

The bash script sees the dollar ($) symbol as a special character used to specify the end of a line or a word.

Example 8 using the-R parameter to recursively find a specific pattern

[Email protected]:~# 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 "linuxtechi" words in the/etc directory

Example 9 using grep to find all empty lines in a file

[Email protected]:~# grep ^$/etc/shadow[email protected]:~#

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

Example 10 using the-I parameter lookup mode

The-i parameter of the grep command ignores the case of characters when looking.

Let's look at an example to find the word "Linuxtechi" in the paswd file.

[Email protected]:~$ grep-i Linuxtechi/etc/passwdlinuxtechi:x:1001:1001::/home/linuxtechi:/bin/bash[email protected]:~$

Example 11 finding multiple modes using the-e parameter

For example, I want to find the ' Linuxtechi ' and ' root ' words in a grep command, and with the-e parameter, we can find multiple patterns.

[Email protected]:~# grep-e "Linuxtechi"-E "root"/etc/passwdroot:x:0:0:root:/root:/bin/bashlinuxtechi:x:1000:1000: Linuxtechi,,,:/home/linuxtechi:/bin/bash[email protected]:~#

Example 12 using the-F file to specify the mode to find

First, create a search mode file "Grep_pattern" in the current directory, and I want to enter the following content in the file.

[Email protected]:~# cat Grep_pattern^linuxtechirootfalse$[email protected]:~#

Now, try searching using the Grep_pattern file

[Email protected]:~# grep-f grep_pattern/etc/passwd

Example of a 14 grep command