title: Sed appears to work but file doesn't change
body: <p>Based on: <a href="https://stackoverflow.com/questions/1074450/sed-replace-part-of-a-line">sed: Replace part of a line</a></p>
  
  <p>I want to modify my <code>sysctl.conf</code> file. The line which contains <code>PermitTunnel something</code> must be changed to <code>PermitTunnel point-to-point</code>.</p>
  
  <p>So using as one man said in the post before, I would use:</p>
  
  <pre><code>sed -e 's/PermitTunnel.*$/PermitTunnel point-to-point/g'
  </code></pre>
  
  <p>Including at the end of the line my file.</p>
  
  <p>Since <code>-n</code> is not used, I guess I'm expected to receive at standar output the result of my operation. Then I executed it and get (notice I'm using <code>-2-</code> instead of <code>-to-</code> just in order to see if I can modify the file as I want, because the file already have the desired line at this case):</p>
  
  <pre><code>root@debian:/home/dit# sed -e 's/PermitTunnel.*$/PermitTunnel point-2-point/g'/etc/sysctl.conf 
  PermitTunnel point-2-point
  </code></pre>
  
  <p>But then I do:</p>
  
  <pre><code>root@debian:/home/dit# cat /etc/sysctl.conf | grep PermitTunnel
  PermitTunnel point-to-point
  </code></pre>
  
  <p>So as you can see, the file has not changed. What am I doing wrong?</p>
  
  <p>Thanks for reading</p>