Regular expression
1. Regular expression single character
| Single character type | Description | Example |
|---|---|---|
| Specific characters
td> | A specific character | ‘1’, a |
| Characters in the range | Single character[] | Numerical characters: [0-9],[259] Lowercase characters:[az] Reverse characters: [^0-9 ] |
| any character | represents any character | ‘.’ |
[[emailprotected] tmp]# grep '1' passwd.bak #Find the line with '1'[[emailprotected] tmp]# grep'[AZ]' passwd .bak #Find all capital letters[[emailprotected] tmp]# grep'[a-zA-Z]' passwd.bak #Find all letters[[emailprotected] tmp]# grep'[,:_/] 'passwd.bak #Find special characters[[emailprotected] tmp]# grep'[^0-9]' passwd.bak #Find lines that do not include numbers [[emailprotected] tmp]# grep'\.' passwd. bak #Find. This character is escaped
2: Representation of other characters
Boundary characters: first and last characters:
^: ^root – —-Begin with root
$:false$ ——End with false
^$: represents a blank line
[[e mail protected] tmp]# grep'^root' passwd.bak[[emailprotected] tmp]# grep'false$' passwd.bak
3: Other characters of regular expression
< p>*Metacharacter: Represents ordinary characters or other characters
| Metacharacters | Description |
|---|---|
| \w lowercase | Match any word character, including underscore ([AZ a-z0-9]) |
| \W uppercase | matches any non-word character, including underscore ([ ^AZ a-z0-9]) |
| \b | represents the separation of words |
[[emailprotected] tmp]# grep'x' passwd.bak #will match x in the x[password] field and the word [[emailprotected] tmp]# grep'\bx\b' passwd.bak #put x is regarded as a word and will not match the x in the word
4: the character combination of regular expressions
| type< /th> | Expression | Example |
|---|---|---|
| String | ‘root’,’1000′,’m..c’,'[ AZ] [az] ” [0-9] [0-9]’ |
[[email protected] tmp]# grep '1000' pas swd.bak oracle:x:1000:1000:oracle:/home/oracle:/bin/bash[[emailprotected] tmp]# grep'[AZ][az]' passwd.bak #match one uppercase next to one Lowercase-a total of 2 characters [[email protected] tmp]# grep'[0-9][0-9]' passwd.bak #match the next 2 digits-a total of 2 digits and greedy match
5: Repeat
? : Match the preceding character or sub-expression 0 or 1 time
+: Match the preceding character or sub-expression 1 or more times
*: 0 or more times Match the preceding character or sub-expression
[[emailprotected] tmp]# grep'\(mail\)\?' passwd.bak #Note that \?,\+ is Match repetition
{n, m}: Repeat a specific number of times
? :{0,1}
+:{1,}
*:{0,}
[[emailprotected] tmp ]# grep'[0-9]\{2,3\}' passwd.bak #: Repeat 2 to 3 times, except for (), all others must be escaped\{\}
6: Any string
.*: represents any string eg: ^.* m.*c ——– represents the beginning of m and the end of c, any length
? m..c—–represents the beginning of m and the end of c, but only 4 digits in length
7: logical representation
|:’ /bin(false|true)’
Common matching patterns:
