Disable robots for staging site

.htaccess

# Use PHP to output robots.txt to avoid accidentally indexing staging sites
RewriteRule  ^robots\.txt$ robots.php [NC,L]

robots.php

<?php

error_reporting(0);

// Default robots - crawl everything
$robotsTxt = "# www.robotstxt.org/
\r\n
# Allow crawling of all content\r\n
User-agent: *";

// If on a staging site prevent indexing, add more domains here if needed
if(strpos($_SERVER['SERVER_NAME'], 'staging.com') !== false){
    $robotsTxt = "User-agent: * \r\nDisallow: /";
}else{

    // read static robots.txt template
    $robotsTxt = @file_get_contents('robots.txt');
}

header('Content-Type:text/plain');
echo $robotsTxt;

robots.txt

# www.robotstxt.org/

# Allow crawling of all content
User-agent: *