title: Use grep to report back only line numbers
body: <p>I have a file that possibly contains bad formatting (in this case, the occurrence of the pattern <code>\\backslash</code>). I would like to use <code>grep</code> to return only the line numbers where this occurs (as in, the match was here, go to line # x and fix it).</p>
  
  <p>However, there doesn't seem to be a way to print the line number (<code>grep -n</code>) and not the match or line itself.</p>
  
  <p>I can use another regex to extract the line numbers, but I want to make sure grep cannot do it by itself. <code>grep -no</code> comes closest, I think, but still displays the match.</p>