title: Why can s command of sed can be followed by a comma?
body: <p>I saw someone use an expression like: <code>sed -e 's, *$,,'</code>
  does anybody know why we can use it like this, and what does it do?</p>
  
  <p>I thought the s command should be <code>sed -e 'addr,addrs/reg/sub/'</code> ?</p>