Table of contents

Linux text search tool--grep

effect

grep is a powerful file search and filtering tool in Linux. It can retrieve file contents according to regular expressions and display the matching results on the screen (matching content will be marked red)

Format

grep -parameter condition filename

parameter

parameter	effect
-i	Ignore case
-c	Count the number of matching rows
-v	Negate , do not display matching lines
-w	match words
-E	Equivalent to egrep, which enables extended regular expressions
-n	Show line number
-rl	Print files in the specified directory
-A number	Match line and n lines below
-B numbers	Match lines and n lines above
-C numbers	Match lines and n lines above and below
-q	Silent mode, no content is output , use $? to determine whether the execution is successful.
-o	Show only matching content

Notice

How it works --- grep can search in one or more files. If the condition contains spaces, you need to use double quotes

Work result --- If the search is successful, a status code of 0 is returned , otherwise a status code of 1 is returned.

Example

Operation object file: /etc/passwd

Function ---Record account information, divided into 7 segments, separated by colons

Meaning ---Account name: Password code x: UID: GID: Comment: Home directory: Login Shell

Notice:

/sbin/nologin in the last paragraph indicates that login is not allowed

grep filter command example

[root@localhost ~]# grep -n "root" /etc/passwd

[root@localhost ~]# grep -n "sshd" /etc/passwd

[root@localhost ~]# grep -n "/sbin/nologin" /etc/passwd

[root@localhost ~]# grep -c "/bin/bash" /etc/passwd

[root@localhost ~]# grep "/bin/bash" /etc/passwd | wc -l

[root@localhost ~]# grep -nv "/sbin/nologin" /etc/passwd

[root@localhost ~]# grep -ni "d" /etc/passwd

[root@localhost ~]# grep -nA2 "ftp" /etc/passwd

[root@localhost ~]# grep -nB3 "ftp" /etc/passwd

[root@localhost ~]# grep -nC3 "ftp" /etc/passwd