PHP regular expression Getting Started Tutorial (recommended), regular expression Getting Started Tutorial _ PHP Tutorial

PHP regular expression Getting Started Tutorial (recommended), regular expression Getting Started Tutorial. PHP regular expression Getting Started Tutorial (recommended), regular expression Getting Started Tutorial mind map click, you can see the specific content! This section introduces regular expressions. in development, you should often use PHP regular expressions. Getting Started (recommended) and regular expressions.

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Introduction

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!

Positioning

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.

Advantages

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

Disadvantages

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

^:

> Put it in the character field (for example, [^ \ w]) to indicate 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.
<?php$regex = '/heL*/i';$str = 'heLLLLLLLLLLLLLLLL';if(preg_match($regex, $str, $matches)){var_dump($matches);}echo "\n";
Result 1.
Code 2
<?php$regex = '/heL*?/i';$str = 'heLLLLLLLLLLLLLLLL';if(preg_match($regex, $str, $matches)){var_dump($matches);}echo "\n";
Result 2:
Code 3: Use "+"
<?php$regex = '/heL+?/i';$str = 'heLLLLLLLLLLLLLLLL';if(preg_match($regex, $str, $matches)){var_dump($matches);}echo "\n";
Result 3:
Code 4: Use {3, 5}
<?php$regex = '/heL{3,10}?/i';$str = 'heLLLLLLLLLLLLLLLL';if(preg_match($regex, $str, $matches)){var_dump($matches);}echo "\n";
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]
 
    
 
   
  
  
The above is a small Editor to introduce you to the PHP regular expression getting started knowledge, hope to help you, if you have any questions, please leave a message, Xiaobian will reply to you in a timely manner. Thank you very much for your support for the help House website!
Attention (recommended), regular expression Getting Started Tutorial mind map click, you can see the specific content! This article introduces regular expressions, which should be frequently used in development...