title: Replace characters in specific columns only (CSV)
body: <p>I have data like this:</p>
  
  <pre><code>1;2015-04-10;23:10:00;10.4.2015 23:10;8.9;1007.5;0.3;0.0;0;55
  2;2015-04-10;23:20:00;10.4.2015 23:20;8.6;1007.8;0.4;0.0;0;56
  3;2015-04-10;23:30:00;10.4.2015 23:30;8.5;1008.1;0.4;0.0;0;57
  </code></pre>
  
  <p>It has dot <code>.</code> as decimal separator but I need to use <code>,</code> instead.</p>
  
  <p>Desired data:</p>
  
  <pre><code>1;2015-04-10;23:10:00;10.4.2015 23:10;8,9;1007,5;0,3;0,0;0;55
  </code></pre>
  
  <p>I tried using <code>Sed</code>. With <code>sed -i 's/\./,/g' myfile.csv</code> I could replace all dots with commas but would destroy dates on the fourth column. How can I change dots to commas in elsewhere but leave the fourth column as it is? If some other <code>Linux</code> tool is better for this task than <code>Sed</code> I could use it as well.</p>