すぐできる！Java100本ノックをSlackに自動投稿するBot ref: http://qiita.com/nesheep5/items/c6a50554199a910af578

file0.js

var URL = "https://github.com/JustSystems/java-100practices/tree/master/contents/";
var TOKEN = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"; // 取得したトークンを貼り付け

function main() {
  // 平日のみ投稿
  var today = new Date();
  if(isJapaneseHoliday(today) || today.getDay() == 0 ||today.getDay() == 6){return;} 

  var qNumRange = SpreadsheetApp.getActiveSheet().getRange(1, 2);
  var qNum = qNumRange.getValue();
  postSlackMessage(qNum);

  // 問題インクリメント
  qNum++;
  if(qNum > 100){ qNum = 1;}
  qNumRange.setValue(qNum);
}


function postSlackMessage(qNum) {
  var slackApp = SlackApp.create(TOKEN); //SlackApp インスタンスの取得

  var options = {
    channelId: "#java100knock",
    userName: "Java100本ノックBot",
    message: "今日の問題はこちら！\n" + 
             URL + ('000' + qNum).slice( -3 ) // 問題番号0埋め         
  };

  slackApp.postMessage(options.channelId, options.message, {username: options.userName});
}

function isJapaneseHoliday(date) {
  var year = date.getFullYear();
  var month = date.getMonth();
  var day = date.getDate();

  var startDate = new Date();
  startDate.setFullYear(year, month-1, day);
  startDate.setHours(0, 0, 0, 0);

  var endDate = new Date();
  endDate.setFullYear(year, month-1, day);
  endDate.setHours(23, 59, 59, 999);

  var cal = CalendarApp.getCalendarById("ja.japanese#holiday@group.v.calendar.google.com");
  var holidays =  cal.getEvents(startDate, endDate);

  return holidays.length != 0;
}