title: substitute only the string concatenate with digits
body: <p>I've tried to substitute the concatenate E with digits (i.e. <code>E1234</code>) into <code>#E1234</code></p>
  
  <p>input</p>
  
  <pre><code>0007 EVENT E0010 RELEASE RESP. 
  EVENT STARt WITH
  E1010 
    E2014
  DE014
  </code></pre>
  
  <p>so by using this command, it should remove only the string with digits.</p>
  
  <pre><code>sed '/E[0-9]/ s/E/\#E/g' input
  </code></pre>
  
  <pre><code>0007 #EV#ENT #E0010 R#EL#EAS#E R#ESP. 
  EVENT STARt WITH
  #E1010 
    #E2014
  D#E014
  
  </code></pre>
  
  <p>It should output something like this. Let me know what you think.</p>
  
  <pre><code>0007 EVENT #E0010 RELEASE RESP. 
  EVENT STARt WITH
  #E1010 
    #E2014
  D#E014
  
  </code></pre>