Shulou(Shulou.com)06/02 Report--

This article introduces how to use grep and egrep commands in Linux. The content is very detailed. Interested friends can use it for reference. I hope it will be helpful to you.

Rep / egrep

Syntax: grep [- cinvABC] 'word' filename

-c: print the number of lines that meet the requirements

-I: ignore case

-n: output together with the line number while outputting the lines that meet the requirements

-v: print lines that do not meet the requirements

-A: followed by a number (with or without spaces). For example, A2 means to print the lines that meet the requirements and the following two lines

-B: followed by a number, such as B2, to print the lines that meet the requirements and the two lines above

-C: followed by a number, such as C2, to print lines that meet the requirements and two lines up and down

Print out the line containing 'halt' and the two lines below this line.

[root@localhost ~] # grep-A2 'halt' / etc/passwdhalt:x:7:0:halt:/sbin:/sbin/haltmail:x:8:12:mail:/var/spool/mail:/sbin/nologinuucp:x:10:14:uucp:/var/spool/uucp:/sbin/nologin

Print out the line containing 'halt' and the two lines above this line.

[root@localhost] # grep-B2 'halt' / etc/passwdsync:x:5:0:sync:/sbin:/bin/syncshutdown:x:6:0:shutdown:/sbin:/sbin/shutdownhalt:x:7:0:halt:/sbin:/sbin/halt

Print out the line containing 'halt', as well as the two lines above and below this line.

Filter out the line with a keyword and output the line number

[root@localhost ~] # grep-n 'root' / etc/passwd1:root:x:0:0:root:/root:/bin/bash11:operator:x:11:0:operator:/root:/sbin/nologin

Filter lines without a keyword and output the line number

[root@localhost ~] # grep-nv 'nologin' / etc/passwd1:root:x:0:0:root:/root:/bin/bash6:sync:x:5:0:sync:/sbin:/bin/sync7:shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown8:halt:x:7:0:halt:/sbin:/sbin/halt26:test:x:511:511::/home/test:/bin/bash27:test1:x:512:511::/home/test1:/bin/bash

Filter out all rows that contain numbers

[root@localhost ~] # grep'[0-9]'/ etc/inittab# upstart works, see init (5), init (8), and initctl (8). # 0-halt (Do NOT set initdefault to this) # 1-Single user mode# 2-Multiuser, without NFS (The same as 3, if you do not have networking) # 3-Full multiuser mode# 4-unused# 5-X1Christ 6-reboot (Do NOT set initdefault to this) id:3:initdefault:

Filter out all rows that do not contain numbers

[root@localhost ~] # grep-v'[0-9]'/ etc/inittab# inittab is only used by upstart for the default runlevel.## ADDING OTHER CONFIGURATION HERE WILL HAVE NO EFFECT ON YOUR SYSTEM.## System initialization is started by / etc/init/rcS.conf## Individual runlevels are started by / etc/init/rc.conf## Ctrl-Alt-Delete is handled by / etc/init/control-alt-delete.conf## Terminal gettys are handled by / etc/init/tty.conf and / etc/init/serial.conf # with configuration in / etc/sysconfig/init.## For information on how to write upstart event handlers, or how## Default runlevel. The runlevels used are:#

Remove all lines starting with'#'

[root@localhost ~] # grep-v'^ #'/ etc/inittabid:3:initdefault:

Remove all blank lines and lines starting with'#'

[root@localhost ~] # grep-v'^ #'/ etc/crontab | grep-v'^ $'SHELL=/bin/bashPATH=/sbin:/bin:/usr/sbin:/usr/binMAILTO=rootHOME=/

In a regular expression, "^" represents the beginning of the line, "$" represents the end of the line, then the blank line can be represented by "^ $", how to print a line that does not start with the English letter?

[root@localhost ~] # vim test.txt [root@localhost ~] # cat test.txt123abc456abc2323#laksdjfAlllllllll

First write a few lines of strings in test.txt to do experiments.

[root@localhost ~] # grep'^ [^ a-zA-Z] 'test.txt123456#laksdjf [root@localhost ~] # grep' [^ a-zA-Z] 'test.txt123456abc2323#laksdjf

If it's a number, use the form [0-9]. Of course, sometimes you can use the form [15], which contains only 1 or 5, note that it doesn't think it's 15. Write [0-9a-zA-Z] if you want to filter out numbers and uppercase and lowercase letters. In addition, [] has another form, that is, the [^ character] represents a character other than the character in [].

Filter any character and repetition character

[root@localhost ~] # grep'r.. o' / etc/passwdoperator:x:11:0:operator:/root:/sbin/nologingopher:x:13:30:gopher:/var/gopher:/sbin/nologinvcsa:x:69:69:virtual console memory owner:/dev:/sbin/nologin

. Represents any character. In the above example, the lines that match two arbitrary characters between r and o are filtered out, and * represents zero or more preceding characters.

[root@localhost ~] # grep 'ooo*' / etc/passwdroot:x:0:0:root:/root:/bin/bashlp:x:4:7:lp:/var/spool/lpd:/sbin/nologinmail:x:8:12:mail:/var/spool/mail:/sbin/nologinuucp:x:10:14:uucp:/var/spool/uucp:/sbin/nologinoperator:x:11:0:operator:/root:/sbin/nologinpostfix:x:89:89::/var/spool/postfix:/sbin/nologin

'ooo*' means oo, ooo, oooo... Or more'o 'now do you have an idea. * what does this combination mean?

[root@localhost ~] # grep'. *'/ etc/passwd | wc-L27 [root@localhost ~] # wc-l / etc/passwd27 / etc/passwd

'. *' indicates zero or more arbitrary characters, and blank lines are included.

Specify the number of times to filter the occurrence of characters

[root@localhost ~] # grep'o\ {2\}'/ etc/passwdroot:x:0:0:root:/root:/bin/bashlp:x:4:7:lp:/var/spool/lpd:/sbin/nologinmail:x:8:12:mail:/var/spool/mail:/sbin/nologinuucp:x:10:14:uucp:/var/spool/uucp:/sbin/nologinoperator:x:11:0:operator:/root:/sbin/nologinpostfix:x:89:89::/var/spool/postfix:/sbin/nologin

Or you don't need the escape character\ plus-E

Grep-E'o {2}'/ etc/passwd

{} is used here, and its interior is a number, indicating the number of times the preceding character is to be repeated. The above example represents a line that contains two o, namely, 'oo'. Note that we need to add the allusion character'\ 'around {}. In addition, we can also represent a range using {}, which is in the format' {N1 ~ N2}'.

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