Linux wildcard characters and regular expressions

Wildcard characters* Any character, can be repeated multiple times? Any character, repeat once
[] represents a characterexample: [a,b,c] means any one of the ABCwildcard characters are used to match the file name of theRegular ExpressionsA regular expression is a string that matches a condition in a file .LS find CP is not supported for regular expressionsbut grep awk sed supports regular expressions

[[email protected] test]#Touch AA[[email protected] test]#Touch AaB Aabb[[email protected] test]#llTotal 0-rw-r--r--1 root root 0 May 16 19:47AA-rw-r--r--1 root root 0 May 16 19:47AaB-rw-r--r--1 root root 0 May 16 19:47Aabb[[email protected]-BIGDATA01 Test]#ls AAAa[[email protected]-BIGDATA01 Test]#ls AA?Aab[[email protected]-BIGDATA01 Test]#ls aa*AA AaB Aabb

Regular Expression Special charactersRegular Expression Match range

Regular expression Standard characters

using regular Expressionsgrep "1"/etc/passwdthe line containing the keyword 1, grep as long as it contains the line, do not want wildcards, to be exactly the same

[[email protected] test]#grep "1"/etc/passwdbin:x:1:1:bin:/bin:/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/nologingames:x:12:100:games:/usr/games:/sbin/nologingopher:x:13:30:gopher:/var/gopher:/sbin/nologinftp:x:14:50:ftp user:/var/ftp:/sbin/nologindbus:x:81:81:system message bus:/:/sbin/nologinusbmuxd:x:113:113:usbmuxd user:/:/sbin/Nologinavahi-autoipd:x:170:170:avahi Ipv4ll stack:/var/lib/avahi-autoipd:/sbin/nologinabrt:x:173:173::/etc/abrt:/sbin/nologinwang:x:501:501::/home/wang:/bin/bash

grep ' root '/etc/passwd
cat/etc/passwd | grep ' root '
That's the same thing, but pipe breaks eat more resources.so1. Match rows with numbers grep ' [0-9] '/etc/passwd 2. Match rows with three digits in a row grep ' [0-9][0-9][0-9] '/etc/passwd or grep ': [0-9][0-9][0-9]: '/etc/ passwd

[[email protected] test]#grep ' [0-9][0-9][0-9] '/etc/passwdgames:x:12:100:games:/usr/games:/sbin/nologinusbmuxd:x:113:113:usbmuxd user:/:/sbin/nologinrtkit:x:499:497:realtimekit:/proc:/sbin/Nologinavahi-autoipd:x:170:170:avahi Ipv4ll stack:/var/lib/avahi-autoipd:/sbin/nologinabrt:x:173:173::/etc/abrt:/sbin/nologinnfsnobody:x:65534:65534:anonymous NFS user:/var/lib/nfs:/sbin/nologinsaslauth:x:498:76:"SASLAUTHD User":/var/empty/saslauth:/sbin/nologinpulse:x:497:496:pulseaudio System daemon:/var/run/pulse:/sbin/nologinliucheng:x:500:500::/home/liucheng:/bin/bashwang:x:501:501::/home/wang:/bin/bas

3. Match lines ending with R beginning with n grep ' ^r.*n$ '/etc/passwd
. * On behalf of all

[[email protected] test] # grep ' ^r.*n$ '  /etc/passwd               rpc:x:32:32:rpcbind daemon:/var/cache/rpcbind:/sbin/nologinrtkit: X:499:497:realtimekit:/proc:/sbin/nologinrpcuser:x:29:29:rpc Service user:/var/lib/nfs:/sbin/ Nologin

4. Filter ifconfig, intercept IPGrep-v represents a reverse intercept, meaning to remove a line with a certain key word sed has the meaning of substitution

[[email protected] test]#ifconfig | grep ' inet addr: 'inet addr:192.168.126.191 bcast:192.168.126.255 mask:255.255.255.0inet Addr:127.0.0.1 mask:255.0.0.0[[Email protected]-BIGDATA01 Test]#[[email protected] test]#ifconfig | grep ' inet addr: ' | grep-v ' 127.0.0.1 'inet addr:192.168.126.191 bcast:192.168.126.255 mask:255.255.255.0[[Email protected]-BIGDATA01 Test]#ifconfig | grep ' inet addr: ' | grep-v ' 127.0.0.1 ' | sed ' s/inet addr://g '192.168.126.191 bcast:192.168.126.255 mask:255.255.255.0[[Email protected]-BIGDATA01 Test]#ifconfig | grep ' inet addr: ' | grep-v ' 127.0.0.1 ' | sed ' s/inet addr://g ' | sed ' s/bcast.*//g '192.168.126.191

Misunderstandinghere is a misunderstanding, think for a long time, is the difference between regular expression and wildcard characterswe know that the wildcard * refers to any character that can be repeated multiple times the regular expression of * refers to the match of the previous character >=0 times these two are completely different, how do you know if I'm using a wildcard or regular expressionat first I fell into a misunderstanding, see the following sequence of commands

[[email protected] test]#Touch AC AAC ABC ABBC[[email protected] test]#llTotal 0-rw-r--r--1 root root 0 May 16 19:55AAC-rw-r--r--1 root root 0 May 16 19:55ABBC-rw-r--r--1 root root 0 May 16 19:55ABC-rw-r--r--1 root root 0 May 16 19:55Ac[[email protected]-BIGDATA01 Test]#ls | grep ' a*c 'Aacabbcabcac[[email protected]-BIGDATA01 Test]#ls | grep ' a.*c 'Aacabbcabcac[[email protected]-BIGDATA01 Test]#ls | grep ' ^a.*c 'Aacabbcabcac[[email protected]-BIGDATA01 Test]#ls | grep ' ^a*c 'AACAC

why grep ' a*c ' and grep ' ^a*c$ ' results will be different, I think one is wildcard, one is regular, because a*c shows four results, justdoes it match any number of characters ? not actuallywildcard characters are used to match the file name of theA regular expression is a string that matches a condition in a file .The use of grep after the pipe break is not a matching file name, this is the operation of the files, so that he is exactly the regular expressiongrep ' A*c ' represents a match a>=0 so as long as C is availablegrep ' ^a*c$ ' is also regular, which means that the second character matches a 0 or more times, followed by the C-letterso only AAC and AC meet the criteriaso look at this example

[[email protected] test] # ls a  AAC  ABB  ABBC  ABC  ac  b  bb  c  cb[[email protected]-BIGDATA01 Test]#  ls | grep ' a*b 'ABBABBCABCBBBCB

Here grep ' a*b ' refers not to A and B but a repeats 0 or more times and then contains B

Linux wildcard characters and regular expressions