title: how to conditionally replace values in columns with value of specific column in the same line by Unix and awk commands
body: <p>I want to conditionally replace values in columns with value of specific column in the same line in one file, by Unix and awk commands.</p>
  
  <p>For example, I have myfile.txt (3 lines, 5 columns, tab-delimited):</p>
  
  <pre><code>1 A . C .
  2 C T . T
  3 T C C .
  </code></pre>
  
  <p>There are "." in columns 3 to 5. I want to replace those "." in columns 3 - 5 with the value in column 2 on the same line.</p>
  
  <p>Could you please show me any directions on that?</p>