Ansible dynamic inventory for docker-machine written in PHP

docker-machine.php

#!/usr/bin/php
<?php
/**
 * Created by IntelliJ IDEA.
 * User: senz
 * Date: 24.04.16
 * Time: 14:54
 */

$opts = getopt('', [
    "list",
    "host:"
]);

if ($argc < 2 || $argc > 3) {
    fwrite(STDERR, "Invalid argument count\n");
    exit(1);
}

if (count($opts) != 1) {
    fwrite(STDERR, "Only one argument must be passed\n");
    exit(1);
}

$machineName = getenv("DOCKER_MACHINE_NAME");
$hostString = getenv("DOCKER_HOST");
$certPath = getenv("DOCKER_CERT_PATH");
if (!$machineName || !$hostString || !$certPath) {
    fwrite(STDERR,
<<<TXT
This script requires env vars:
DOCKER_MACHINE_NAME
DOCKER_HOST
DOCKER_CERT_PATH
And optional GROUPS_FILE with json describing groups attributes 
(see https://docs.ansible.com/ansible/developing_inventory.html)

TXT
    );
    exit(1);
}

$sshPrivateKey = $certPath . DIRECTORY_SEPARATOR . "id_rsa";
$parsedHost = parse_url($hostString);
$host = $parsedHost['host'];
$groupsFile = getenv("GROUPS_FILE");

$out = "";
if (isset($opts['list'])) {
    if (!$groupsFile || !is_readable($groupsFile)) {
        $out = "{}";
    } else {
        $content = file_get_contents($groupsFile);
        $json = json_decode($content, true);
        if (null === $json) {
            fwrite(STDERR, "Groups files cannot be decoded\n");
            exit(1);
        } else {
            $out = $content;
        }
    }

} elseif (isset($opts['host'])) {
    if ($opts['host'] == $machineName) {
        $json = [
            "ansible_host" => $host,
            "ansible_ssh_private_key_file" => $sshPrivateKey,
            "ansible_user" => "docker",
        ];
        $out = json_encode($json);
    } else {
        $out = "{}";
    }
} else {
    fwrite(STDERR, "Abnormal crap\n");
    exit(1);
}
echo $out . "\n";
exit(0);