title: powershell : replace character in TXT file in certain position
body: <p>Hello I have a txt file like this (name test.txt)</p>
  
  <pre><code>        Z     , HADEtatPat ,"HAD : Evolution de l'‚tat du patient" ,44                           
  ////////B     , HADDialyse ,"Dialyse hors centre depuis HAD"   , 21                          
         W     , HADAutre   ,"HAD : Hors protocole"            , 13                    
  //        p     , HADPIA     ,"HAD : PIA sejour vers SSR/PSY"     , 17                      
          x     , HADS‚aEJ   ,"D‚part vers S‚ance de Chimio./Radioth‚./Dialyse dansé " , 22
  </code></pre>
  
  <p>I want replace the character 1 and 2 of line 4 by '@@'</p>
  
  <p>how to do this</p>
  
  <p>I try</p>
  
  <pre><code>Get-Content test.txt | Select -Index 3 | replace-char position 1,2 by '@' | replace-content test.txt
  </code></pre>
  
  <p>but not working
  thx for help</p>
  
  <p>I need</p>