title: Insert text mid-line with sed/awk
body: <p>I want to insert a character between two numbers: <code>foo bar 12 34</code> to become <code>foo bar 12/34</code>.</p>
  
  <p>So I want something like <code>sed</code> to match a space found between two numbers and substitute that with a slash, but I'm not sure how to do it.</p>
  
  <p>I have <code>sed -e 's/[1-9][0-9] [1-9][0-9]/\//'</code> so far, but I know that substitues both numbers <em>and</em> the space with the slash. I need to find the space in the line that's between two numbers, but only substitute the space. Maybe I need <code>grep</code> to find it, but I still need the entire line to print in the end.</p>
  
  <p>Any ideas?</p>