title: How to find missing files(dates) among thousands of files in a folder?
body: <p>I have several daily files for the years 2003-2009. the total number of the files is 2546 so there are missing dates(files) .I do not want to look on file by another to find out which dats are missing?.
  the files are named like this:</p>
  
  <pre><code> dat_20030129_gf.img   # so the date change from file to another
  </code></pre>
  
  <p>any command in Linux to perform this please</p>