title: How to replace spaces with points at even positions in a line using linux command
body: <p>I have a file where I am trying to replace the <strong>spacing</strong> at even positions with two points. What linux command Can I use to do it?</p>
  <p>I tried the following sed command <code>sed 's/\s/:/2'</code> from <a href="https://superuser.com/questions/143392/replace-nth-occurence-of-string-in-each-line-of-a-text-file">replace nth occurence of string in each line of a text file</a> But it only replaces the second occurence.</p>
  <hr />
  <h1>input</h1>
  <pre><code>TEDL15_TRAINING_00018 2 0.047883321 6 0.041573718 7 0.020443868 8 0.035350464 11 0.026124746 16 0.035317142 22 0.014992127
  
  TEDL15_TRAINING_00015 2 0.076135024 66 0.036367059 68 0.05614619 106 0.040146504 113 0.038728137 
  </code></pre>
  <hr />
  <h1>output</h1>
  <pre><code>TEDL15_TRAINING_00018 2:0.047883321 6:0.041573718 7:0.020443868 8 0.035350464 11:0.026124746 16:0.035317142 22:0.014992127
      
  TEDL15_TRAINING_00015 2:0.076135024 66:0.036367059 68:0.05614619 106: 0.040146504 113:0.038728137 
  </code></pre>