protected function processDockerfileVariables()
    {
        $variables = [];
        $variables['PHP_VERSION'] = $this->getVersion();

        foreach ($this->configs as $key => $values) {
            if (!in_array($key, static::DOCKER_VARIABLES)) {
                continue;
            }

            if ($key === 'PHP_EXT_ENABLE'
                && !empty($this->configs['PHP_PECL'])) {
                $php_pecl = $this->configs['PHP_PECL'];

                // Remove the version from the PECL package.
                array_walk($php_pecl, function (&$name) {
                    $pos = strpos($name, ':');
                    if ($pos !== false) {
                        $name = substr($name, 0, $pos);
                    }
                });
                $values = array_merge($php_pecl, $values);
            }

            if (empty($values)) {
                continue;
            }

            $variables[$key] = $this->formatVariables($key, $values);
        }

        return $variables;
    }