How Can I Detect and Linkify URLs in PHP Text Using Regular Expressions?

Detect and Linkify URLs in Text

When working with user-supplied text, it's often necessary to identify and linkify URLs embedded within the text. Here's how to achieve this in PHP:

Using a Regular Expression

To detect URLs, you can use the following regular expression:

$rexProtocol = '(https?://)?';
$rexDomain   = '((?:[-a-zA-Z0-9]{1,63}\.)+[-a-zA-Z0-9]{2,63}|(?:[0-9]{1,3}\.){3}[0-9]{1,3})';
$rexPort     = '(:[0-9]{1,5})?';
$rexPath     = '(/[!$-/0-9:;=@_\':;!a-zA-Z\x7f-\xff]*?)?';
$rexQuery    = '(\?[!$-/0-9:;=@_\':;!a-zA-Z\x7f-\xff]+?)?';
$rexFragment = '(#[!$-/0-9:;=@_\':;!a-zA-Z\x7f-\xff]+?)?';

$regex = "&\b$rexProtocol$rexDomain$rexPort$rexPath$rexQuery$rexFragment(?=[?.!,;:\"]?(\s|$))&";

This regular expression will match:

• Optional protocol (http:// or https://)
• Domain name or IP address
• Optional port number
• Optional path
• Optional query string
• Optional fragment identifier

Creating Hyperlinks

Once URLs are detected, you can use the following callback function to create HTML hyperlinks:

function callback($match)
{
    $completeUrl = $match[1] ? $match[0] : "http://{$match[0]}";

    return '<a href="' . $completeUrl . '">'
        . $match[2] . $match[3] . $match[4] . '</a>';
}

This function prepends "http://" if no protocol is specified and creates an HTML anchor tag with the detected URL as the href attribute.

Applying the Regex and Callback

Finally, you can use preg_replace_callback to apply the regular expression and create hyperlinks for all detected URLs:

$text = "Here are some URLs: stackoverflow.com/questions/1188129/pregreplace-to-detect-html-php";

print preg_replace_callback($regex, 'callback', htmlspecialchars($text));

This will output the text with detected URLs converted into clickable links.

Additional Considerations

• To prevent XSS attacks, escape user-supplied text before processing it with the regular expression.
• The provided regular expression does not support all URL syntax variations. You may need to refine it based on your specific requirements.
• Email addresses can also be detected and hyperlinked using a similar approach.

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