slackit.php

<?php
$url     = "https://hooks.slack.com/services/[Incoming-Webhook-URL]";

$msg = "Test";
parse_str($_SERVER['QUERY_STRING'], $output);
$msg     = $output['message'];
$payload = 'payload={"channel": "#channel", "username": "bot-username", "text": "' . $msg . '"}';

$ch = curl_init();
curl_setopt($ch, CURLOPT_POST, TRUE);
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_POSTFIELDS, $payload);

curl_exec($ch);
curl_close($ch);

?>