Google Docs add on to update a "field" on open

updateLastUpdated

/**
 * Written by diyclassics
 *
 * Looks for text in a Google Doc on open in the form "last updated 1/1/2001" and updates
 * with the current date; also adds a menu item for manual update.
 */

function onOpen() {
  var ui = DocumentApp.getUi();
  // Or FormApp or SpreadsheetApp.
  ui.createMenu('Scripts')
      .addItem('Update Last Updated Date', 'updateLastUpdated')
      .addToUi();

updateLastUpdated();  
  
}

function getCurrentDate() {
  var date = new Date();
  var year = date.getYear();
  var month = date.getMonth() + 1;
  var day = date.getDate(); if(day.toString().length==1){var day = day;}
  return month + '.' + day + '.' + year;
}


function updateLastUpdated() {
  var currentDate = getCurrentDate();
  var body = DocumentApp.getActiveDocument().getBody();
  body.replaceText("last updated .+", 'last updated ' + currentDate);
}