shlink/module/Common/functions/functions.php

<?php
if (! function_exists('env')) {
    /**
     * Gets the value of an environment variable. Supports boolean, empty and null.
     * This is basically Laravel's env helper
     *
     * @param string $key
     * @param mixed $default
     * @return mixed
     * @link https://github.com/laravel/framework/blob/5.2/src/Illuminate/Foundation/helpers.php#L369
     */
    function env($key, $default = null)
    {
        $value = getenv($key);
        if ($value === false) {
            return $default;
        }

        switch (strtolower($value)) {
            case 'true':
            case '(true)':
                return true;
            case 'false':
            case '(false)':
                return false;
            case 'empty':
            case '(empty)':
                return '';
            case 'null':
            case '(null)':
                return null;
        }

        return trim($value);
    }
}