Verify the validity of URLs. Regular expressions or built-in functions are commonly used in PHP. 1. Use regularity to flexibly match standard URLs, such as ^(?:https?://)?(?:[\da-z.-] ).(?:[az.-]{2,6})(?:[/\w.-])/?$ can identify addresses with protocols, domain names and paths; 2. If stricter verification is required, protocol headers and specification path characters can be mandatory; 3. It is recommended to use filter_var($url, FILTER_VALIDATE_URL) first, because it has good compatibility and supports complex situations such as IPv6, ports, and parameters, and the syntax is concise and reliable.

Verifying the effectiveness of URLs is a common requirement in PHP development, such as in form submission, data cleaning, or crawling projects. Verifying URLs with regular expressions (regex) is a direct and effective way, but it is not easy to write them accurately.

The most commonly used method in PHP is to combine filter_var() function and the FILTER_VALIDATE_URL filter. However, if you have more specific format requirements or want to understand the underlying implementation logic, it is also feasible to write a regex yourself.

Basic URL regular expressions

A common and standard rule that matches most standard URLs is as follows:

 _^(https?:\/\/)?([\da-z\.-] )\.([az\.]{2,6})([\/\w \.-]*)*\/?$_

Let’s explain the structure of this regularity:

• ^ and $ : indicates a complete match to avoid the situation where irrelevant characters are mixed in the middle.
• (https?:\/\/)? : Allow http or https, and the entire protocol part is optional.
• ([\da-z\.-] ) : Domain name body, containing letters, numbers, points and horizontal lines.
• \.([az\.]{2,6}) : Top-level domain names, such as .com, .net, .co.uk, etc., with a length limit of 2~6 characters.
• ([\/\w \.-]*)*\/? : The path part, supports multi-level directories, file names, spaces (actually recommended to filter spaces), special symbols, etc.

This expression can match addresses like http://example.com/path/to/page.php , example.com , and https://sub.domain.co.uk/ .

Stricter URL verification methods

If you want the URL to have a protocol (http/https) and the path cannot be too complicated, you can write it like this:

 _^(https?:\/\/)([\da-z\.-] )\.([az]{2,6})(\/[\w\.-]*)*\/?$_

Change points:

• Removed the protocol ? , forced to bring http:// or https://
• The path part does not allow spaces or other special characters, only basic characters / , . , - , letters and numbers

This writing method is more suitable for user input verification to prevent some irregular URLs from being mixed into the system.

Examples for using PHP

You can use preg_match() to match:

 $url = "https://example.com/path/to/page";
$pattern = '/^(https?:\/\/)([\da-z\.-] )\.([az]{2,6})(\/[\w\.-]*)*\/?$/i';

if (preg_match($pattern, $url)) {
    echo "URL is in correct format";
} else {
    echo "URL is illegal";
}

A few things to note:

• Adding the i modifier can make the domain name case insensitive (for example, allow Example.Com )
• If you accept local development environments such as localhost , you can add \b(localhost)\b as an exception to the domain name part
• If you want to allow query parameters (such as ?id=123 ), you need to extend the path part and add support for ? and &

Other methods: filter_var() is simpler

Although regularity is flexible, it is recommended to use PHP built-in functions in most cases:

 if (filter_var($url, FILTER_VALIDATE_URL)) {
    echo "valid URL";
}

It has handled various edge cases internally, such as IPv6 addresses, port numbers, query parameters, etc., and the syntax is clear and error-prone.

In general, it is feasible to verify the URL with regularity, but pay attention to details, such as whether the protocol is optional, whether the path allows special characters, whether the top-level domain length is required, etc. If you don't pursue complete customization, it's easier to prioritize built-in functions.

The above is the detailed content of php regex for url validation. For more information, please follow other related articles on the PHP Chinese website!