search
HomeBackend DevelopmentPHP TutorialIn-depth analysis of sub-patterns of regular expressions

In-depth analysis of sub-patterns of regular expressions

Dec 09, 2017 am 11:45 AM
modelIn-depth analysisexpression

在正则表达式中,可以使用“(”和“)”将模式中的子字符串括起来,以形成一个子模式。将子模式视为一个整体时,那么它就相当于一个单个字符。下面我们就来详细了解下子模式

首先,我们先看一段PHP代码:

<?php
  $time = date ("Y-m-d H:i:s");
  $pattern = "/\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2}/i"; 
  if(preg_match($pattern,$time,$arr)){
  echo "<pre class="brush:php;toolbar:false">";
  print_r($arr);    
  echo "
";   } ?>

显示结果:

Array
(
  [0] => 2012-06-23 03:08:45
)

有没有注意到,显示的结果只有一条数据,即符合匹配模式的时间格式,那如果只有一条记录的话,为什么还要用数组保存呢?直接使用字符串保存不是更好?

带着这个问题,我们来看下正则表达式中的子模式。

在正则表达式中,可以使用“(”和“)”将模式中的子字符串括起来,以形成一个子模式。将子模式视为一个整体时,那么它就相当于一个单个字符。

比如,我们将以上的代码稍微修改下,改成如下:

<?php
  $time = date ("Y-m-d H:i:s");
  $pattern = "/(\d{4})-(\d{2})-(\d{2}) (\d{2}):(\d{2}):(\d{2})/i"; 
  if(preg_match($pattern,$time,$arr)){
  echo "<pre class="brush:php;toolbar:false">";
  print_r($arr);    
  echo "
";   } ?>

注意:我只修改了$pattern,在匹配模式中,使用了括号()

执行结果:

Array
(
  [0] => 2012-06-23 03:19:23
  [1] => 2012
  [2] => 06
  [3] => 23
  [4] => 03
  [5] => 19
  [6] => 23
)

总结:我们可以使用小括号给整个匹配模式进行分组,默认情况下,每个分组会自动拥有一个组号,规则是,从左到右,以分组的左括号为标志,第一个出现的分组为组号1,第二个为组号2,以此类推。其中,分组0对应整个正则表达式。
对整个正则匹配模式进行了分组以后,就可以进一步使用“向后引用”来重复搜索前面的某个分组匹配的文本。例如:\1代表分组1匹配的文本,\2代表分组2匹配的文本等等
我们可以进一步修改下代码,如下所示:

<?php
  $time = date ("Y-m-d H:i:s");
  $pattern = "/(\d{4})-(\d{2})-(\d{2}) (\d{2}):(\d{2}):(\d{2})/i";
  $replacement = "\$time格式为:$0<BR>替换后的格式为:\\1年\\2月\\3日 \\4时\\5分\\6秒";
  print preg_replace($pattern, $replacement, $time);
  if(preg_match($pattern,$time,$arr)){
    echo "<pre class="brush:php;toolbar:false">";
    print_r($arr);    
    echo "
";   } ?>

注意:

因为是在双引号中,所以使用分组的时候应该使用两个反斜杠,如:\\1,而如果在单引号中,则使用一个反斜杠就可以了,如:\1
\\1用于捕获分组一种的内容:2012,\\6用于捕获分组6中的内容          
执行结果:

$time格式为:2012-06-23 03:30:31
替换后的格式为:2012年06月23日 03时30分31秒
Array
(
  [0] => 2012-06-23 03:30:31
  [1] => 2012
  [2] => 06
  [3] => 23
  [4] => 03
  [5] => 30
  [6] => 31
)

相关推荐:

php表单中常用的正则表达式总结

php中关于表单常用正则表达式的使用总结

php中关于正则表达式应用的详解

The above is the detailed content of In-depth analysis of sub-patterns of regular expressions. For more information, please follow other related articles on the PHP Chinese website!

Statement
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
Explain the concept of a PHP session in simple terms.Explain the concept of a PHP session in simple terms.Apr 26, 2025 am 12:09 AM

PHPsessionstrackuserdataacrossmultiplepagerequestsusingauniqueIDstoredinacookie.Here'showtomanagethemeffectively:1)Startasessionwithsession_start()andstoredatain$_SESSION.2)RegeneratethesessionIDafterloginwithsession_regenerate_id(true)topreventsessi

How do you loop through all the values stored in a PHP session?How do you loop through all the values stored in a PHP session?Apr 26, 2025 am 12:06 AM

In PHP, iterating through session data can be achieved through the following steps: 1. Start the session using session_start(). 2. Iterate through foreach loop through all key-value pairs in the $_SESSION array. 3. When processing complex data structures, use is_array() or is_object() functions and use print_r() to output detailed information. 4. When optimizing traversal, paging can be used to avoid processing large amounts of data at one time. This will help you manage and use PHP session data more efficiently in your actual project.

Explain how to use sessions for user authentication.Explain how to use sessions for user authentication.Apr 26, 2025 am 12:04 AM

The session realizes user authentication through the server-side state management mechanism. 1) Session creation and generation of unique IDs, 2) IDs are passed through cookies, 3) Server stores and accesses session data through IDs, 4) User authentication and status management are realized, improving application security and user experience.

Give an example of how to store a user's name in a PHP session.Give an example of how to store a user's name in a PHP session.Apr 26, 2025 am 12:03 AM

Tostoreauser'snameinaPHPsession,startthesessionwithsession_start(),thenassignthenameto$_SESSION['username'].1)Usesession_start()toinitializethesession.2)Assigntheuser'snameto$_SESSION['username'].Thisallowsyoutoaccessthenameacrossmultiplepages,enhanc

What are some common problems that can cause PHP sessions to fail?What are some common problems that can cause PHP sessions to fail?Apr 25, 2025 am 12:16 AM

Reasons for PHPSession failure include configuration errors, cookie issues, and session expiration. 1. Configuration error: Check and set the correct session.save_path. 2.Cookie problem: Make sure the cookie is set correctly. 3.Session expires: Adjust session.gc_maxlifetime value to extend session time.

How do you debug session-related issues in PHP?How do you debug session-related issues in PHP?Apr 25, 2025 am 12:12 AM

Methods to debug session problems in PHP include: 1. Check whether the session is started correctly; 2. Verify the delivery of the session ID; 3. Check the storage and reading of session data; 4. Check the server configuration. By outputting session ID and data, viewing session file content, etc., you can effectively diagnose and solve session-related problems.

What happens if session_start() is called multiple times?What happens if session_start() is called multiple times?Apr 25, 2025 am 12:06 AM

Multiple calls to session_start() will result in warning messages and possible data overwrites. 1) PHP will issue a warning, prompting that the session has been started. 2) It may cause unexpected overwriting of session data. 3) Use session_status() to check the session status to avoid repeated calls.

How do you configure the session lifetime in PHP?How do you configure the session lifetime in PHP?Apr 25, 2025 am 12:05 AM

Configuring the session lifecycle in PHP can be achieved by setting session.gc_maxlifetime and session.cookie_lifetime. 1) session.gc_maxlifetime controls the survival time of server-side session data, 2) session.cookie_lifetime controls the life cycle of client cookies. When set to 0, the cookie expires when the browser is closed.

See all articles

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

Video Face Swap

Video Face Swap

Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Tools

MinGW - Minimalist GNU for Windows

MinGW - Minimalist GNU for Windows

This project is in the process of being migrated to osdn.net/projects/mingw, you can continue to follow us there. MinGW: A native Windows port of the GNU Compiler Collection (GCC), freely distributable import libraries and header files for building native Windows applications; includes extensions to the MSVC runtime to support C99 functionality. All MinGW software can run on 64-bit Windows platforms.

PhpStorm Mac version

PhpStorm Mac version

The latest (2018.2.1) professional PHP integrated development tool

SublimeText3 Linux new version

SublimeText3 Linux new version

SublimeText3 Linux latest version

mPDF

mPDF

mPDF is a PHP library that can generate PDF files from UTF-8 encoded HTML. The original author, Ian Back, wrote mPDF to output PDF files "on the fly" from his website and handle different languages. It is slower than original scripts like HTML2FPDF and produces larger files when using Unicode fonts, but supports CSS styles etc. and has a lot of enhancements. Supports almost all languages, including RTL (Arabic and Hebrew) and CJK (Chinese, Japanese and Korean). Supports nested block-level elements (such as P, DIV),

Dreamweaver Mac version

Dreamweaver Mac version

Visual web development tools