title: simple unix script to check a txt file and do another job
body: <p>I have two bat scripts: A.bat and B.bat. A.bat generates a txt file (year.txt) that contains the last year of simulation, such as 2005. </p>
  
  <p>I want the A.bat to check the year.txt every 30 seconds. If the year.txt shows 2005, then the A.bat will call the B.bat.</p>
  
  <p>Please teach me how to do this. Thanks a lot.</p>