Comprehensive Guide to PHP Regular Expressions with Practical Examples

M66 2025-08-04

Understanding PHP Regular Expressions

Regular expressions are powerful tools widely used in PHP for string matching and manipulation. This article systematically introduces the basic usage and practical examples of PHP regular expressions to help readers quickly grasp their core concepts.

Basic Regular Expression Syntax

The most commonly used function for regex matching in PHP is preg_match(). Here are the core regex syntax elements:

Metacharacters:

^ : Matches the beginning of a string
$ : Matches the end of a string
. : Matches any single character
* : Matches zero or more of the preceding character
+ : Matches one or more of the preceding character
? : Matches zero or one of the preceding character
[] : Matches any one character inside the brackets
| : Logical OR operator
() : Grouping operator

Special Characters:

\d : Matches a digit
\w : Matches a letter, digit, or underscore
\s : Matches a whitespace character

Quantifiers:

{n} : Matches exactly n times of the preceding character
{n,} : Matches at least n times of the preceding character
{n,m} : Matches between n and m times of the preceding character

Common Regular Expression Examples

Matching Email Addresses

$email = "example@example.com";
if(preg_match("/^\w+([.-]?\w+)*@\w+([.-]?\w+)*(\.\w{2,3})+$/", $email)){
    echo "Valid Email Address!";
}else{
    echo "Invalid Email Address!";
}

Matching Phone Numbers

$phone = "13812345678";
if(preg_match("/^1[3456789]\d{9}$/", $phone)){
    echo "Valid Phone Number!";
}else{
    echo "Invalid Phone Number!";
}

Extracting Content Inside HTML Tags

$html = '<div><p>Hello, World!</p></div>';
preg_match("/<p>(.*?)<\/p>/", $html, $matches);
echo "Extracted Content: " . $matches[1];

Replacing Content Within a String

$oldStr = "Hello, PHP!";
$newStr = preg_replace("/PHP/", "World", $oldStr);
echo "Replaced String: " . $newStr;

Checking if a String Contains a Specific Word

$str = "Hello, World!";
if(preg_match("/World/", $str)){
    echo "The string contains 'World'!";
}else{
    echo "The string does not contain 'World'!";
}

Advanced Applications of Regular Expressions

Beyond basic matching, regular expressions support capture groups and assertions that enable more complex matching logic. The following example shows how to extract sentences containing a specific keyword:

$text = "I love PHP. PHP is a powerful language. PHP is widely used.";
preg_match_all("/(.*?PHP.*?)./", $text, $matches);
foreach($matches[1] as $sentence){
    echo $sentence . ".";
}

This article’s examples provide a thorough understanding of PHP regular expression syntax and practical skills, allowing you to apply them flexibly in everyday development tasks. Mastery of regex is a vital skill for efficient and high-quality coding. We hope this guide aids your learning journey, and encourage you to continue exploring and practicing based on your projects.

preg_match