gistfile1.cs

using RestSharp;

void ContentServicePublished(IPublishingStrategy sender, PublishEventArgs<IContent> e)
{
  foreach (var entity in e.PublishedEntities)
  {
    var umbracoHelper = new UmbracoHelper(UmbracoContext.Current);
    var url = umbracoHelper.Url(entity.Id, UrlProviderMode.Relative);

    var urls = string.Format("https://slacker.moriyama.co.uk{0} or http://slacker.moriyama.int{0}", url);
    var t = "New publish : " + entity.Name + " " + urls;

    var hash = "bot@moriyama.co.uk".HashEmailForGravatar();
    var client = new RestClient("https://slack.com/api");

    var request = new RestRequest("/chat.postMessage", Method.POST);
    request.AddParameter("token", "<top-secret>");
    request.AddParameter("channel", "#mychannel");
    request.AddParameter("username", "Moriyama Bot");
    request.AddParameter("text", t);
    request.AddParameter("icon_url", string.Format("http://www.gravatar.com/avatar/{0}", hash));

    var response = client.Execute(request);
  }
}