当前位置：网站首页>Regular expression

Regular expression

2022-07-01 18:40:00 【Hadron's blog】

One , What is regular expression

Regular expressions , Also known as regular expression . In code it is often abbreviated as regex、regexp or RE）, A concept of computer science . Regular expressions are often used for retrieval 、 Replace those that match a pattern ( The rules ) The text of . There is more than one regular expression , and LINUX Different programs in may use different regular expressions , Tools ：grep sed awk egrep

Regular expressions --- It is usually used to judge , Used to check whether a string satisfies a certain format ;

Regular expressions are composed of ordinary characters and metacharacters. Ordinary characters include upper and lower case letters 、 Numbers 、 Punctuation and some other symbolic metacharacters refer to special characters with special significance in regular expressions , It can be used to specify its leading characters （ The character before the metacharacter ） The occurrence pattern in the target object

Two , Basic regular expressions

Common metacharacters in basic regular expressions ：( Supported tools ：grep、egrep、sed、awk)

      
      
       
        Special characters 
       
       
\： Escape character , Escape special characters , Ignore its special significance a\.b matching a.b, But can't match ajb,. Be escaped as a special meaning 
       
       

       
       
^： Match the beginning of the line ,^ Is the beginning of the matching string ^tux Match with tux Beginning line ^^^^
       
       

       
       
$： Match the end of the line ,$ Is the end of the matching string tux$ Match with tux The line at the end $$$$ 
       
       

       
       
.： Match break \r\n Any single character other than 
       
       

       
       
[list]： matching list A character in the list   example ： go[ola]d,[abc]、[a-z]、[a-z0-9]
       
       

       
       
[^list]： Any match is not in list A character in the list   example ： [^a-z]、[^0-9]、[^A-Z0-9]
       
       

       
       
*： Match the front face expression 0 Times or more   example ：goo*d、go.*d
       
       

       
       
\{n\} : Match the previous subexpression n Time , example :go\{2\}d、'[O-9]\{2\}' Match two numbers 
       
       

       
       
\{n,\}: Match the preceding subexpression no less than n Time , example : go\{2,\}d、' [0-9]\{2,\}' Match two or more digits 
       
       

       
       
\{n,m\}﹔ Match the previous subexpression n To m Time , example : go\{2,3\)d、'[0-9]\{2,3\}' Match two to three digits 
       
       

       
       
 notes : egrep、awk Use {n}、{n, }、{n, m} When the match “{}" There is no need to add "\”
       
       
egrep -E -n 'wo{2}d' test.txt   //-E  Used to display the qualified characters in the file 
       
       
egrep -E -n 'wo{2,3}d' test.txt
      
      
      
      
       
       1.
       
       2.
       
       3.
       
       4.
       
       5.
       
       6.
       
       7.
       
       8.
       
       9.
       
       10.
       
       11.
       
       12.
       
       13.
       
       14.
       
       15.
       
       16.
       
       17.
       
       18.
       
       19.
       
       20.
       
       21.
       
       22.
       
       23.
       
       24.

      
      
       
        Locator 
       
       
^  Matches where the input string starts 
       
       
$  Matches the position of the end of the input string 
       
       

       
       
 Nonprinting characters 
       
       
\n  Match a line break 
       
       
\r  Match a carriage return 
       
       
\t  Match a tab 
      
      
      
      
       
       1.
       
       2.
       
       3.
       
       4.
       
       5.
       
       6.
       
       7.
       
       8.

3、 ... and , Extended regular expression

      
      
       
       ( Supported tools : egrep、 awk)
       
       

       
       
+ : Match the front face expression 1 More than once , example : go+d,  Will match at least one o,  Such as god、 good、 goood etc. 
       
       

       
       
? : Match the front face expression 0 Time or 1 Time , example : go?d,  Will match gd or god
       
       

       
       
() : Use the string in parentheses as h all in one , example 1: g(oo)+d,"  Will match oo whole 1 More than once , Such as good、gooood etc. 
       
       

       
       
| : Match a string of words by or , example : g (oo|la)d,"  Will match good perhaps glad
      
      
      
      
       
       1.
       
       2.
       
       3.
       
       4.
       
       5.
       
       6.
       
       7.
       
       8.
       
       9.