PHP regular expression Getting Started Tutorial

PHP regular expression Getting Started Tutorial [go] mind map

Click to view details!

Regular expressions are frequently used in development. many development languages now have regular expressions, such as javascript, java, and ,. net, php, etc. today I will share my understanding of regular expressions with you. For more information, please advise!

What terms do you need to know ?? How many terms do you know?

Delta delimiters

Delta character Field

Delta modifier

△Qualifier

△Delimiters

△Wildcard (forward pre-query, reverse pre-query)

△Reverse reference

△Inert match

Delta annotation

△0 character width

When should we use regular expressions? Not all character operations use regular expressions, but php uses regular expressions in some ways, which affects efficiency. Regular expressions are a good choice when parsing complex text data.

When processing complex character operations, regular expressions can improve the efficiency and reduce the amount of code.

When we use regular expressions, complex regular expressions increase the complexity of the code, making it hard to understand. So sometimes we need to add comments inside the regular expression.

General mode

The delimiter. "/" is usually used as the delimiter to start and end. you can also use "#".

When can I use? Generally, when your string contains many "/" characters, this character needs to be escaped during regular expressions, such as uri.

The code for using the "/" delimiter is as follows.

$regex = '/^http:\/\/([\w.]+)\/([\w]+)\/([\w]+)\.html$/i';$str = 'http://www.youku.com/show_page/id_ABCDEFG.html';$matches = array();if(preg_match($regex, $str, $matches)){    var_dump($matches);}echo "\n";

$ Matches [0] in preg_match will contain strings that match the entire pattern.

The code for using the "#" delimiter is as follows. at this time, "/" is not escaped!

$regex = '#^http://([\w.]+)/([\w]+)/([\w]+)\.html$#i';$str = 'http://www.youku.com/show_page/id_ABCDEFG.html';$matches = array();if(preg_match($regex, $str, $matches)){    var_dump($matches);}echo "\n";

Modifier: used to change the behavior of a regular expression.

We can see ('/^ http: \/([\ w.] +) \/([\ w] +) \/([\ w] + )\. the last "I" in html/I ') is a modifier, indicating that the case is ignored. another commonly used one is "x", which indicates that spaces are ignored.

Contribution code:

$regex = '/HELLO/';$str = 'hello word';$matches = array();if(preg_match($regex, $str, $matches)){    echo 'No i:Valid Successful!',"\n";}if(preg_match($regex.'i', $str, $matches)){    echo 'YES i:Valid Successful!',"\n";}

Character field: [\ w] The expanded part in square brackets is the character field.

Token qualifier: for example, [\ w] {3, 5}, [\ w] *, or [\ w] + the symbols after these [\ w] indicate the delimiter. This section describes the specific meaning.

{3, 5} represents 3 to 5 characters. {3,} is more than 3 characters, {, 5} is up to 5 characters, and {3} is three characters.

* 0 to multiple

+ Indicates one or more.

Escape character

^:

> In the character field (for example, [^ \ w]), it indicates no (excluding the meaning )?? "Reverse selection"

> Put it before the expression to start with the current character. (/^ N/I, which indicates starting with n ).

Note that "\" is often called "escape character ". Used to escape some special symbols, such ".","/"

Wildcard (lookarounds): determines whether some characters in some strings exist!

Lookarounds can be divided into two types: lookaheads (forward pre-query? =) And lookbehinds (reverse pre-query? <= ).

> Format:

Forward pre-query :(? =) Corresponding (?!) Negative meaning

Reverse pre-query :(? <=) Corresponds (?

Followed by characters

$ Regex = '/(? <= C) d (? = E)/';/* d followed by c, d followed by e */$ str = 'abcdefg'; $ matches = array (); if (preg_match ($ regex, $ str, $ matches) {var_dump ($ matches);} echo "\ n ";

Negative meaning:

$ Regex = '/(?
     
    
 
   
   
   
> Character width: Zero
   
Verify the zero-character code
   
    
     
$regex = '/HE(?=L)LO/i';$str = 'HELLO';$matches = array();if(preg_match($regex, $str, $matches)){    var_dump($matches);}echo "\n";
    
    
No result is printed!
    
     
$regex = '/HE(?=L)LLO/i';$str = 'HELLO';$matches = array();if(preg_match($regex, $str, $matches)){    var_dump($matches);}echo "\n";
    
    
Can print the result!
    
Note :(? = L) it means that HE is followed by an L character. But (? = L) it does not take up any character. it must be differentiated from (L). (L) itself occupies one character.
   
   
Capture data
   
Groups that do not specify the type will be obtained for future use.
   
> The specified type indicates a wildcard. Therefore, only the starting position of parentheses without question marks can be captured.
   
   
> References in the same expression are called reverse references.
   
> Call Format: \ number (for example, \ 1 ).
   
    
     
$regex = '/^(Chuanshanjia)[\w\s!]+\1$/';    $str = 'Chuanshanjia thank Chuanshanjia';$matches = array();if(preg_match($regex, $str, $matches)){    var_dump($matches);}echo "\n";
    
    
 
    
> Avoid data capture
    
Format :(? : Pattern)
    
Advantage: The number of valid reverse references will be minimized, and the code will be clearer.
    
> Named capture group
    
Format :(? P
  <组名>
   
) Call method (? P = group name)
  
    
     
      
$regex = '/(?Pchuanshanjia)[\s]Is[\s](?P=author)/i';$str = 'author:chuanshanjia Is chuanshanjia';$matches = array();if(preg_match($regex, $str, $matches)){    var_dump($matches);}echo "\n";
     
     
Running result
     
    
    
    
     
Inertia matching (remember: two operations will be performed. please refer to the following principles)
    
    
Format: qualifier?
    
Principle :"? ": If there is a qualifier before, the smallest data will be used. For example, "*" takes 0, and "+" takes 1. for example, if it is {3, 5}, it takes 3.
    
Let's take a look at the following two codes:
    
Code 1.
    
     
      
    
Result 1.
    
    
 
    
Code 2
    
     
       
    
Result 2:
    
    
 
    
Code 3: Use "+"
    
     
        
    
Result 3:
    
    
Code 4: Use {3, 5}
    
     
         
    
Result 4:
    
   
   
   
Regular expression comments
   
Format :(? # Comment)
   
Purpose: it is mainly used for complex annotations.
   
Contributed code: a regular expression used to connect to the MYSQL database
   
    
     
$ Regex = '/^ host = (?
          
    
 
   
   
Special characters
   
         
      
      
      
       
       
 
        
 
         
Special characters
 
         
Explanation
 
        
 
        
 
         
*
 
         
0 to multiple times
 
        
 
        
 
         
+
 
         
1 to multiple times can also be written as {1 ,}
 
        
 
        
 
         
?
 
         
0 or 1 time
 
        
 
        
 
         
.
 
         
Match all single characters except line breaks
 
        
 
        
 
         
\ W
 
         
[A-zA-Z0-9 _]
 
        
 
        
 
         
\ S
 
         
Blank characters (space, line break, carriage return) [\ t \ n \ r]
 
        
 
        
 
         
\ D
 
         
[0-9]
 
        
 
       
      
      
   
   
 
   
Original article: http://www.cnblogs.com/baochuan/archive/2012/03/12/2391135.html