How to detect search engine bots with PHP?

Search engine bots can be detected in PHP by analyzing the $_SERVER['HTTP_USER_AGENT'] string, which contains information about the client making the request. Bot detection is useful for serving different content or implementing specific behaviors for search engines.

Method 1: Using strstr() Function

This method checks if a specific bot name exists in the user agent string ?

<?php
if(strstr(strtolower($_SERVER['HTTP_USER_AGENT']), "googlebot")) {
    echo "Google bot detected!";
} else {
    echo "Regular user detected.";
}
?>

Code explanation − The strtolower() function converts the user agent to lowercase for case-insensitive comparison, then strstr() searches for the bot name within the string.

Method 2: Using Regular Expressions

A more comprehensive approach using preg_match() to detect multiple bot types ?

<?php
function _bot_detected() {
    return (
        isset($_SERVER['HTTP_USER_AGENT'])
        && preg_match('/bot|crawl|slurp|spider|mediapartners/i', $_SERVER['HTTP_USER_AGENT'])
    );
}

if (_bot_detected()) {
    echo "Search engine bot detected!";
} else {
    echo "Human visitor detected.";
}
?>

Code explanation − The preg_match() function uses a regular expression pattern to match common bot keywords. The i flag makes the search case-insensitive.

Enhanced Bot Detection

A more detailed function that identifies specific bot types ?

<?php
function detectBot() {
    $user_agent = $_SERVER['HTTP_USER_AGENT'] ?? '';
    $bots = [
        'googlebot' => 'Google',
        'bingbot' => 'Bing',
        'slurp' => 'Yahoo',
        'facebookexternalhit' => 'Facebook',
        'twitterbot' => 'Twitter'
    ];
    
    foreach ($bots as $bot => $name) {
        if (stripos($user_agent, $bot) !== false) {
            return $name . ' Bot';
        }
    }
    
    return false;
}

$bot = detectBot();
echo $bot ? "Detected: $bot" : "Human visitor";
?>

Conclusion

Use strstr() for simple bot detection or preg_match() with regular expressions for comprehensive checking. Always validate the $_SERVER['HTTP_USER_AGENT'] exists before processing to avoid errors.