Linking URLs in Strings with PHP

Linking URLs in strings can be a useful task in PHP for tasks such as generating clickable links in textual content. One common use case is converting a plain string containing URLs into HTML with clickable hyperlinks.

Syntax:

$string = preg_replace(
  "~[[:alpha:]] ://[^<>[:space:]] [[:alnum:]/]~",
  "<a href=\"\\0\">\\0</a>",
  $string
);

Explanation:

• Regex Pattern: The pattern used in preg_replace matches strings starting with a protocol prefix (e.g., "http://") followed by one or more alphanumeric characters, excluding angle brackets and whitespace. It ends with alphanumeric characters or a slash.
• Replacement String: The replacement string includes HTML markup to create an anchor () tag with the matched URL as the href attribute and the original URL as the text content.

Example:

$input = "Look on http://www.google.com";
$output = preg_replace(
  "~[[:alpha:]] ://[^<>[:space:]] [[:alnum:]/]~",
  "<a href=\"\\0\">\\0</a>",
  $input
);

echo $output; // Output: "Look on http://www.google.com"

PHP Versions:

This solution is compatible with both PHP versions prior to 5.3 (using ereg_replace) and PHP 5.3 and later (using preg_replace).