https://mmonit.com/wiki/MMonit/SlackNotification

slack-webhook.rb

#!/usr/bin/ruby

require 'net/https'
require 'json'

uri = URI.parse("https://hooks.slack.com/services/XXXXXXXXX/YYYYYYYYY/ZZZZZZZZZZZZZZZZZZZZZZZZ")
http = Net::HTTP.new(uri.host, uri.port)
http.use_ssl = true
request = Net::HTTP::Post.new(uri.request_uri, {'Content-Type' => 'application/json'})
request.body = {
    "channel"  => "#general",
    "username" => "mmonit",
    "text"     => "[#{ENV['MONIT_HOST']}] #{ENV['MONIT_SERVICE']} - #{ENV['MONIT_DESCRIPTION']}"
}.to_json
response = http.request(request)
puts response.body