Sample file for regex issue with repeat patterns

regex-sample.txt

---
title: Newsletter Design Issues with Outlook 2010
layout: post
permalink: /2012/04/newsletter-design-issues-with-outlook-2010/
categories:
  - Code
  - Design
  - Web Dev
  
  
// The regex should find all categories 
// categories can range from 1 to unknown (well, sort of…)
// output them in the following format:    categories: Code, Design, Web Dev
  
  // The most inefficient regex used, creating a separate pattern for every category, 7 in this case: 
  
  categories:\r\s+-\s?((.+)\s?)(\r\s+-\s?(.+)\s?)(\r\s+-\s?(.+)\s?)(\r\s+-\s?(.+)\s?)(\r\s+-\s?(.+)\s?)(\r\s+-\s?(.+)\s?)(\r\s+-\s?(.+)\s?)(\r\s+-\s?(.+)\s?)
  
  // replace pattern: 
  categories: \1, \4, \6, \8, \10, \12, \14, \16\r
  
  // then change to 6 categories, 5… and repeat. Duh…
  // What I wanted was somthing like this: 
  
  categories:\r\s+-\s?((.+)\s?)(\r\s+-\s?(.+)\s?){1,}
  
  // but this doesn't work :(
  // even if this would work, there's no way feed it the commas I guess
  // thanks for giving it a shot ;) 
  
  
  

Thanks guys! Will give it a shot. Looks like it's not possible to achieve in one pass, which I was curious about.
Leaving out categories: and starting to think at the end of the line seems to work quite well also, but still (or only) leaves one , at the end of the line.

\n\s+-\s?(.+)$ and replace with: \1,