use Gettext\Scanner\PhpScanner;
use Gettext\Generator\PoGenerator;
use Gettext\Translations;
//Create a new scanner, adding a translation for each domain we want to get:
$phpScanner = new PhpScanner(
    Translations::create('domain1'),
    Translations::create('domain2'),
    Translations::create('domain3')
);
//Set a default domain, so any translations with no domain specified, will be added to that domain
$phpScanner->setDefaultDomain('domain1');
//Extract all comments starting with 'i18n:' and 'Translators:'
$phpScanner->extractCommentsStartingWith('i18n:', 'Translators:');
//Scan files
foreach (glob('*.php') as $file) {
    $phpScanner->scanFile($file);
}
//Save the translations in .po files
$generator = new PoGenerator();
foreach ($phpScanner->getTranslations() as $domain => $translations) {
    $generator->generateFile($translations, "locales/{$domain}.po");
}