Detect current environment and define as a global constant.

envirions.php

<?php

/**
 * Detect current environment and define as a global constant.
 * @param array $environments Associative-Array where the keys are environment
 * names and it's values the URI's that should be matched. Environment URI's can
 * be string or an array of strings. If no environment URI is matched sets 
 * current environment as a first key element of an environments array.
 * @param string $constant_name Name of the constant enfironment should be
 * assigned to.
 * @return boolean TRUE if an environment URI was matched, FALSE otherwise.
 * @author Otar Chekurishvili
 * @version 1.0
 * @license http://www.opensource.org/licenses/MIT The MIT License
 */
function envirions($environments = array(), $constant_name = 'ENV')
{
    foreach ($environments AS $environment => $uri)
    {
        $current_uri = $_SERVER['SERVER_NAME'] . $_SERVER['REQUEST_URI'];
        if (is_string($uri) AND FALSE !== strpos($current_uri, $uri))
        {
            define($constant_name, $environment);
            break;
        }
        elseif (is_array($uri))
        {
            foreach ($uri AS $sub_uri)
            {
                if (FALSE !== strpos($current_uri, $sub_uri))
                {
                    define($constant_name, $environment);
                    break;
                }
            }
            if (defined($constant_name))
            {
                break;
            }
            else
            {
                continue;
            }
        }
        else
        {
            continue;
        }
    }
    if (!defined($constant_name))
    {
        if (empty($environments))
        {
            return false;
        }
        else
        {
            $environments = array_keys($environments);
            define($constant_name, $environments[0]);
        }
    }
    return TRUE;
}

example.php

<?php

require_once 'envirions.php';

envirions(array(
    'development' => array(
        'localhost.com',
        'local.domain'
    ),
    'testing' => 'test.domain.com',
    'production' => array(
        'domain.com',
        'alternative.domain.com'
    )
));