title: How do I quickly append using sed the same word to the end of many different lines of one file
body: <p>The original file would be:</p>
  
  <pre><code>line 1
  line 2
  line 3
  line 4
  line 5
  .
  .
  .
  line N
  </code></pre>
  
  <p>and I want to append some text (e.g."word") every X lines until the end of the file is reached, like this: (X=2 in example)</p>
  
  <pre><code>line 1 word
  line 2
  line 3 word
  line 4
  line 5 word
  line 6
  line 7 word
  .
  .
  .
  line N
  </code></pre>
  
  <p>N is of the order of 100000. 
  With the program I made (using sed) I had to wait for about 15 minutes to finish. I'm sure there is a much quicker way to do it.</p>