title: Match rest of string with regex
body: <p>I have a string like this</p>
  
  <pre><code>ch:keyword
  ch:test
  ch:some_text
  </code></pre>
  
  <p>I need a regular expression which will match all of the strings, however, it must not match the following:</p>
  
  <pre><code>ch: (ch: is proceeded by a space, or any number of spaces)
  ch: (ch: is proceeded by nothing)
  </code></pre>
  
  <p>I am able to deduce the length of the string with the 'ch:' in it.
  Any help would be appreciated; I am using PHP's preg_match()</p>
  
  <p>Edit: I have tried this:</p>
  
  <pre><code>preg_match("/^ch:[A-Za-z_0-9]/", $str, $matches)
  </code></pre>
  
  <p>However, this only matches 1 character after the string. I tried putting a * after the closing square bracket, but this matches spaces, which I don't want.</p>