Summary of grep commands

Use and summary of grep command

Grep is best at filtering content / matching content.

The commonly used parameters are as follows

-v: excludes lines that have already matched the content (the smallest unit is: lines)

-o: only show the content that is received, it doesn't have any effect, don't remember it

-A: on the current line that matches the content, how many pieces of content are displayed behind the After= >

-B: on the current line that matches the content, how many pieces of content Beforce= > the previous meaning are displayed to the front

-C: on the current line that matches the content, how many pieces of content Center= > middle meaning are displayed at the center of the current behavior?

-the extended parameter of E:egrep plus it can match multiple conditions at one time, but should be separated by vertical bars |

-n: the line number that displays the content

It is recommended to use double quotes when using grep to match content

Examples are as follows:

1. Match the word hadoop in the / etc/passwd file

[root@oldboyLinux ~] # grep "hadoop" / etc/passwdhadoop:x:500:500::/home/hadoop:/bin/bash

2. The use of the parameter-v excludes the content with ftp. Do not display all lines with the word ftp.

[root@oldboyLinux ~] # grep-v "ftp" / etc/passwdroot:x:0:0:root:/root:/bin/bashbin:x:1:1:bin:/bin:/sbin/nologin.tcpdump:x:72:72::/:/sbin/nologinoprofile:x:16:16:Special user account to be used by OProfile:/home/oprofile:/sbin/nologinhadoop:x:500:500::/home/hadoop:/bin/bash

3. Use regular expressions to match

If you want to filter out all configuration files that are annotated and exclude all lines that begin with #

[root@oldboyLinux etc] # grep-v "^ #" / etc/udev/rules.d/70-persistent-net.rules

4. Match the content ending with what character

[root@oldboyLinux etc] # grep "nologin$" / etc/passwd

5. Grep can also display the use of the line number-n parameter of the file content.

[root@oldboyLinux etc] # grep-n. / etc/passwd1:root:x:0:0:root:/root:/bin/bash2:bin:x:1:1:bin:/bin:/sbin/nologin3:daemon:x:2:2:daemon:/sbin:/sbin/nologin4:adm:x:3:4:adm:/var/adm:/sbin/nologin5:lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin6:sync:x:5:0:sync:/sbin:/bin/sync7:shutdown : x:6:0:shutdown:/sbin:/sbin/shutdown8:halt:x:7:0:halt:/sbin:/sbin/halt9:mail:x:8:12:mail:/var/spool/mail:/sbin/nologin10:uucp:x:10:14:uucp:/var/spool/uucp:/sbin/nologin11:operator:x:11:0:operator:/root:/sbin/nologin12:games:x:12:100:games:/usr/games:/sbin/nologin13:gopher:x : 13:30:gopher:/var/gopher:/sbin/nologin14:ftp:x:14:50:FTP User:/var/ftp:/sbin/nologin15:nobody:x:99:99:Nobody:/:/sbin/nologin16:dbus:x:81:81:System message bus:/:/sbin/nologin17:vcsa:x:69:69:virtual console memory owner:/dev:/sbin/nologin18:abrt:x:173:173::/etc/abrt:/sbin/nologin19:haldaemon:x:68: 68:HAL daemon:/:/sbin/nologin20:ntp:x:38:38::/etc/ntp:/sbin/nologin21:saslauth:x:499:76: "Saslauthd user": / var/empty/saslauth:/sbin/nologin22:postfix:x:89:89::/var/spool/postfix:/sbin/nologin23:sshd:x:74:74:Privilege-separated SSH:/var/empty/sshd:/sbin/nologin24:tcpdump:x:72:72::/:/sbin/nologin25:oprofile: X:16:16:Special user account to be used by OProfile:/home/oprofile:/sbin/nologin26:hadoop:x:500:500::/home/hadoop:/bin/bash