title: how to extract certain columns of a file and save them in new file
body: <p>I have a file which contains lines of data in the following format:</p>
  
  <pre><code>a11 a12 a13 a14 a15
  a21 a22 a23 a24 a25 
  a31 a32 a33 a34 a35 
  a41 a42 a43 a44 a45 
  .
  .
  .
  </code></pre>
  
  <p>what I need is to save this data in a new file with the following format after performing some arithmetic on it:</p>
  
  <pre><code>a11 
  a12*x1 a13/y1 z1*a15+d1
  a21 
  a22*x2 a23/y2 z2*a25+d2
  a31 
  a32*x3 a33/y3 z3*a35+d3
  .
  .
  .
  .
  </code></pre>
  
  <p>all the xi, yi, zi and di are float numbers. These numbers are stored ina second file having the format:</p>
  
  <pre><code>x1 y1 z1 d1
  x2 y2 z2 d2
  x3 y3 z3 d3
  .
  .
  .
  </code></pre>
  
  <p>I really appreciate it if you could please guide with a csh or bash snippet on how this can be done.</p>
  
  <p>Cheers</p>