title: Bash shell script to find missing files from filename
body: <p>I have a folder that should contain 1485 files, named PA0001.png, PA0002.png ... up to PA1485.png</p>
  
  <p>Some of them are missing and I'd like to write a shell script able to identify the missing ones and print them, as a list, in a .txt file (preferably without the leading string PA and the .png extension, but with the leading zeroes, if any)</p>
  
  <p>I have no clue on how to proceed though, maybe using awk? But I'm still quite of a noob... Any help would be much appreciated!</p>