grep command:
grep is a powerful text search tool. It checks the target file line by line based on the user-specified "" and filter conditions written by regular expression metacharacters, prints the matched lines, and prints to the terminal window by default.
Regular expression: A pattern written by a type of special characters and text characters, andDoes not represent the literal meaning，Express control or wildcard function。
用法：
grep [OPTIONS] PATTERN [FILE...]
grep [OPTIONS] [-e PATTERN | -f FILE] [FILE...]
| –color=auto | Highlight the matched text |
|---|---|
| -i | Ignore character case |
| -n | Show line number |
| -E | Support the use of extended regular expressions |
| -O | Print the matched line |
| -v | Display the lines that cannot be matched |
| -A# | Next few lines |
| -B # | First few lines |
| -C # | A few lines before and after |
[root@localhost ~]# grep --color=auto "UUID" /etc/fstab
UUID=05f664d6-53c8-4e53-9291-b1321936d79c / ext4 defaults 1 1
UUID=758db803-7a5d-493b-be16-68ca2d050d55 /boot ext4 defaults 1 2
UUID=93fc053e-b9a0-4439-a822-3575ee7f3f3d swap swap defaults 0 0
Matches:
| * | Match the preceding character any number of times. 0 times, 1 time or multiple times |
|---|---|
| .* | Match any character of any length |
| \? | Match the character on the face 0 or 1, at most once |
| \+ | Match the character before it one or more times, at least once |
| \{m\} | Match the preceding character m times |
| \{m,n\} | Match the preceding character at least m times and at most n times |
| \{0,n\} | At most n times |
| \{m,\} | At least m times |
实例：
[root@localhost tmp]# cat file
xxxxxy
xyxyxyxyxy
xyyyyxsakfxy
xakfafhlkashfyasbx
asflaklkfhxy
[root@localhost tmp]# grep --color=auto（高量显示，找到的字符用其他颜色标出） x*y file（前面的x出现0次或者多次y出现一次）
xxxxxy
xyxyxyxyxy
xyyyyxsakfxy
xakfafhlkashfyasbx
asflaklkfhxy
[root@localhost tmp]# grep "x\{2,4\}y" file（记得加引号）
xxxxxy
Position anchoring:
| ^ | Anchor at the beginning of the line for the leftmost side of the pattern |
|---|---|
| $ | End-of-line anchoring, used on the rightmost side of the pattern |
| ^ $ | blank line |
| ^pattern$ | Use pattern to match the entire line |
| \< | Anchor at the beginning of a word, used on the left side of a word |
| \> | Suffix anchoring, used on the right side of words |
| \<pattern\> | Anchored as a pattern |
1.显示/etc/passwd文件中不以/bin/bash结尾的行
[root@localhost tmp]# grep -v '/bin/bash&' /etc/passwd
root:x:0:0:root:/root:/bin/bash
bin:x:1:1:bin:/bin:/sbin/nologin
daemon:x:2:2:daemon:/sbin:/sbin/nologin
adm:x:3:4:adm:/var/adm:/sbin/nologin
lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
sync:x:5:0:sync:/sbin:/bin/sync
shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
halt:x:7:0:halt:/sbin:/sbin/halt
mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
uucp:x:10:14:uucp:/var/spool/uucp:/sbin/nologin
operator:x:11:0:operator:/root:/sbin/nologin
games:x:12:100:games:/usr/games:/sbin/nologin
gopher:x:13:30:gopher:/var/gopher:/sbin/nologin
ftp:x:14:50:FTP User:/var/ftp:/sbin/nologin
nobody:x:99:99:Nobody:/:/sbin/nologin
vcsa:x:69:69:virtual console memory owner:/dev:/sbin/nologin
saslauth:x:499:76:Saslauthd user:/var/empty/saslauth:/sbin/nologin
postfix:x:89:89::/var/spool/postfix:/sbin/nologin
sshd:x:74:74:Privilege-separated SSH:/var/empty/sshd:/sbin/nologin
apache:x:48:48:Apache:/var/www:/sbin/nologin
2.显示/etc/passwd中的两位数或者三位数
[root@localhost tmp]# grep '\<[[:digit:]]\{2,3\}\>' /etc/passwd
mail:x:8:12:mail:/var/spool/mail:/sbin/nologin
uucp:x:10:14:uucp:/var/spool/uucp:/sbin/nologin
operator:x:11:0:operator:/root:/sbin/nologin
games:x:12:100:games:/usr/games:/sbin/nologin
gopher:x:13:30:gopher:/var/gopher:/sbin/nologin
ftp:x:14:50:FTP User:/var/ftp:/sbin/nologin
nobody:x:99:99:Nobody:/:/sbin/nologin
vcsa:x:69:69:virtual console memory owner:/dev:/sbin/nologin
saslauth:x:499:76:Saslauthd user:/var/empty/saslauth:/sbin/nologin
postfix:x:89:89::/var/spool/postfix:/sbin/nologin
sshd:x:74:74:Privilege-separated SSH:/var/empty/sshd:/sbin/nologin
apache:x:48:48:Apache:/var/www:/sbin/nologin
3.找出 netstat -tan 命令结果中以LISTEN后跟一个或者多个空白字符结尾的行
[root@localhost tmp]# netstat -tan | grep "LISTEN[[:space:]]\{1,\}$"
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN
tcp 0 0 127.0.0.1:25 0.0.0.0:* LISTEN
tcp 0 0 :::22 :::* LISTEN
tcp 0 0 ::1:25 :::* LISTEN
Grouping:
| \(\) | Group, bundle one or more characters together and treat them as a whole |
|---|
Quote:
| \1 | Starting from the left of the pattern, the characters matched by the pattern between the first left bracket and the matching right bracket |
|---|---|
| \2 | Starting from the left of the pattern, the characters matched by the pattern between the second left parenthesis and the matching right parenthesis |
| # | Starting from the left of the pattern, the characters matched by the pattern between the #th left bracket and the matching right bracket |
实例：
[root@localhost tmp]# cat file
He loves his lover.
He likes his lover.
She likes her liker.
She loves her liker.
[root@localhost tmp]# grep "\(h\).*\(l..e\).*\1.*\2" file
She likes her liker.
To find out the IP address in the ifconfig command?
[root@localhost tmp]# ifconfig
eth0 Link encap:Ethernet HWaddr 00:0C:29:B6:F8:F4
inet addr:192.168.176.128 Bcast:192.168.176.255 Mask:255.255.255.0
inet6 addr: fe80::20c:29ff:feb6:f8f4/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:3493 errors:0 dropped:0 overruns:0 frame:0
TX packets:1659 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:283560 (276.9 KiB) TX bytes:183236 (178.9 KiB)
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:65536 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:0 (0.0 b) TX bytes:0 (0.0 b)
[root@localhost tmp]# ifconfig | grep "\(192\).*[[:digit:]]$" | cut -d ":" -f 2 | cut -d " " -f 1
192.168.176.128