title: Change Names of Multiple Files Linux
body: <p>I have a number of files with names a1.txt, b1.txt, c1,txt...on ubuntu machine.</p>
  
  <p>Is there any quick way to change all file names to a2.txt, b2.txt, c2.txt...?</p>
  
  <p>In particular, I'd like to replace part of the name string. For instance, every file name contains a string called "apple" and I want to replace "apple" with "pear" in all file names.</p>
  
  <p>Any command or script?</p>