Home Backend Development PHP Tutorial Learn regular expressions in PHP with examples_PHP tutorial

Learn regular expressions in PHP with examples_PHP tutorial

Jul 13, 2016 pm 04:58 PM
php match and character string study Example us regular of expression first

First of all, let’s take a look at two special characters: ‘^’ and ‘$’. They are used to match the beginning and end of a string respectively. Let’s illustrate each with examples


"^The": Matches strings starting with "The";
"of despair$": matches strings ending with "of despair";
"^abc$": Matches strings starting with abc and ending with abc. In fact, only abc matches it
"notice": Matches strings containing notice


You can see that if you don't use the two characters we mentioned (the last example), it means that the pattern (regular expression) can appear anywhere in the string being tested, and you don't lock it to both sides
There are also several characters '*', ' ', and '?', which are used to represent the number or order of occurrences of a character. They respectively represent: "zero or more", "one or more", and "zero or one." Here are some examples:


"ab*": Matches a string consisting of string a and 0 or more b ("a", "ab", "abbb", etc.);
"ab ": Same as above, but with at least one b ("ab", "abbb", etc.);
"ab?": matches 0 or one b;
"a?b $": Matches a string ending with one or 0 a plus one or more b.


You can also limit the number of characters within curly braces, such as


"ab{2}": matches an a followed by two b (not one less) ("abb");
"ab{2,}": update at least two b("abb", "abbbb", etc.);
"ab{3,5}": 2-5 b("abbb", "abbbb", or "abbbbb").



You must also note that you must always specify (i.e., "{0,2}", not "{,2}"). Likewise, you must note that '*', ' ', and '?' respectively The following three range annotations are the same, "{0,}", "{1,}", and "{0,1}".

Now put a certain number of characters into parentheses, for example:


"a(bc)*": matches a followed by 0 or one "bc";
"a(bc){1,5}": one to 5 "bc."


There is also a character '│', which is equivalent to the OR operation:


"hi│hello": matches strings containing "hi" or "hello";
"(b│cd)ef": matches strings containing "bef" or "cdef";
"(a│b)*c": Match contains - multiple (including 0) a or b, followed by a c
string of string;


A dot ('.') can represent all single characters:


"a.[0-9]": an a followed by a character followed by a number (strings containing such a string will be matched, this bracket will be omitted in the future)
"^.{3}$": ends with three characters .


The content enclosed in square brackets only matches a single character


"[ab]": matches a single a or b (same as "a│b");
"[a-d]": matches a single character from 'a' to 'd' (same effect as "a│b│c│d" and "[abcd]");
"^[a-zA-Z]": Matches strings starting with letters
"[0-9]%": Matches strings containing x%
",[a-zA-Z0-9]$": Matches a string ending with a comma followed by a number or letter


You can also list the characters you don't want in brackets. You just need to use '^' as the beginning of the bracket (i.e., "%[^a-zA-Z]%" matches two percent signs. There is a non-letter string inside).

In order to be able to explain, but "^.[$()│* ?{" is a character with special meaning, you must add '' in front of these characters, and in php3 you should avoid using it at the beginning of the pattern , for example, the regular expression "($│?[0-9] " should be called ereg("($│?[0-9] ", $str) (I don’t know if it is the same in php4)

Don’t forget that characters inside square brackets are exceptions to this rule

www.bkjia.comtruehttp: //www.bkjia.com/PHPjc/631397.htmlTechArticleFirst, let’s take a look at two extraordinary characters: ^ and $. They are used to match strings respectively. Let’s take an example of the beginning and end. ^The: Matches strings starting with The; of...
Statement of this Website
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

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

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment

Dreamweaver CS6

Dreamweaver CS6

Visual web development tools

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)

PHP 8.4 Installation and Upgrade guide for Ubuntu and Debian PHP 8.4 Installation and Upgrade guide for Ubuntu and Debian Dec 24, 2024 pm 04:42 PM

PHP 8.4 brings several new features, security improvements, and performance improvements with healthy amounts of feature deprecations and removals. This guide explains how to install PHP 8.4 or upgrade to PHP 8.4 on Ubuntu, Debian, or their derivati

7 PHP Functions I Regret I Didn't Know Before 7 PHP Functions I Regret I Didn't Know Before Nov 13, 2024 am 09:42 AM

If you are an experienced PHP developer, you might have the feeling that you’ve been there and done that already.You have developed a significant number of applications, debugged millions of lines of code, and tweaked a bunch of scripts to achieve op

How To Set Up Visual Studio Code (VS Code) for PHP Development How To Set Up Visual Studio Code (VS Code) for PHP Development Dec 20, 2024 am 11:31 AM

Visual Studio Code, also known as VS Code, is a free source code editor — or integrated development environment (IDE) — available for all major operating systems. With a large collection of extensions for many programming languages, VS Code can be c

Explain JSON Web Tokens (JWT) and their use case in PHP APIs. Explain JSON Web Tokens (JWT) and their use case in PHP APIs. Apr 05, 2025 am 12:04 AM

JWT is an open standard based on JSON, used to securely transmit information between parties, mainly for identity authentication and information exchange. 1. JWT consists of three parts: Header, Payload and Signature. 2. The working principle of JWT includes three steps: generating JWT, verifying JWT and parsing Payload. 3. When using JWT for authentication in PHP, JWT can be generated and verified, and user role and permission information can be included in advanced usage. 4. Common errors include signature verification failure, token expiration, and payload oversized. Debugging skills include using debugging tools and logging. 5. Performance optimization and best practices include using appropriate signature algorithms, setting validity periods reasonably,

PHP Program to Count Vowels in a String PHP Program to Count Vowels in a String Feb 07, 2025 pm 12:12 PM

A string is a sequence of characters, including letters, numbers, and symbols. This tutorial will learn how to calculate the number of vowels in a given string in PHP using different methods. The vowels in English are a, e, i, o, u, and they can be uppercase or lowercase. What is a vowel? Vowels are alphabetic characters that represent a specific pronunciation. There are five vowels in English, including uppercase and lowercase: a, e, i, o, u Example 1 Input: String = "Tutorialspoint" Output: 6 explain The vowels in the string "Tutorialspoint" are u, o, i, a, o, i. There are 6 yuan in total

How do you parse and process HTML/XML in PHP? How do you parse and process HTML/XML in PHP? Feb 07, 2025 am 11:57 AM

This tutorial demonstrates how to efficiently process XML documents using PHP. XML (eXtensible Markup Language) is a versatile text-based markup language designed for both human readability and machine parsing. It's commonly used for data storage an

Explain late static binding in PHP (static::). Explain late static binding in PHP (static::). Apr 03, 2025 am 12:04 AM

Static binding (static::) implements late static binding (LSB) in PHP, allowing calling classes to be referenced in static contexts rather than defining classes. 1) The parsing process is performed at runtime, 2) Look up the call class in the inheritance relationship, 3) It may bring performance overhead.

What are PHP magic methods (__construct, __destruct, __call, __get, __set, etc.) and provide use cases? What are PHP magic methods (__construct, __destruct, __call, __get, __set, etc.) and provide use cases? Apr 03, 2025 am 12:03 AM

What are the magic methods of PHP? PHP's magic methods include: 1.\_\_construct, used to initialize objects; 2.\_\_destruct, used to clean up resources; 3.\_\_call, handle non-existent method calls; 4.\_\_get, implement dynamic attribute access; 5.\_\_set, implement dynamic attribute settings. These methods are automatically called in certain situations, improving code flexibility and efficiency.

See all articles