title: RegEx: Match a character and (possibly) the one before
body: <p>I am trying to find a regex that matches a particular character and if and only if the character before is a space, match it as well.</p>
  
  <p>E.g.: the character I am looking for is "a", then in "this is a test" there should " a" be matched (including the space).</p>
  
  <p>Since there is no logical "and", how do you do it?</p>
  
  <p>Thanks in advance.</p>