function showStatus(){
  var mySheet = SpreadsheetApp.getActiveSheet();
  var myCell = mySheet.getActiveCell(); 
  var ss = SpreadsheetApp.getActiveSpreadsheet(); 
  var ss_url = ss.getUrl();
  if(myCell.getColumn()==4){
    var message = myCell.getValue() + ss_url;
    slackPost(message);
  } 
}
function slackPost(message){
  var url        = 'https://slack.com/api/chat.postMessage';
  var token      = 'URL';
  var channel    = 'channel';
  var username   = 'タスク更新通知BOT';
  var parse      = 'full';
  var icon_emoji = ':tada:';
  var method     = 'post'; 
  var payload = {
    'token'      : token,
    'channel'    : channel,
    'text'       : message + '  @mention',
    'username'   : username,
    'parse'      : parse,
    'icon_emoji' : icon_emoji
  };
  var params = {
    'method' : method,
    'payload' : payload
  };
  var response = UrlFetchApp.fetch(url, params);
}