WP-Mix

This quick PHP snippet can be used to check if a specific URL exists. I use this in one of my projects for checking the existence of a robots.txt file on the site. Can be modified to check for files on any publicly accessible site.

$protocol = is_ssl() ? 'https://' : 'http://'; // uses WP function is_ssl()
$robots   = $protocol . $_SERVER['SERVER_NAME'] .'/robots.txt';
$exists   = false;

if (!$exists && in_array('curl', get_loaded_extensions())) {
	
	$ch = curl_init($robots);   
	 
	curl_setopt($ch, CURLOPT_NOBODY, true);
	curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
	curl_exec($ch);
	
	$response = curl_getinfo($ch, CURLINFO_HTTP_CODE);
	
	if ($response === 200) $exists = true;
	
	curl_close($ch);
	
}

if (!$exists && function_exists('get_headers')) {
	
	$headers = @get_headers($robots);
	
	if ($headers) {
		
		if (strpos($headers[0], '404') !== false) {
			
			$exists = true;
			
		}
		
	}
	
}

Here is how this works:

1. Sets three variables: $protocol, $robots, and $exists
2. Check if PHP’s curl is available; if so, then use it to check for the specified URL ($robots variable)
3. Check if get_headers is available; if so, then use it to check for the specified URL ($robots variable)

So the end result of this script will be that the $exists variable will return as true if the specified file/URL exists. Otherwise $exists remains false.

Notes: If WordPress is not available, you’ll need to modify or remove the $protocol variable accordingly. Also may want to change the $robots variable throughout depending on usage. And lastly, make sure to specify the URL of whichever resource/file you want to check.