Regex Tip - Don't Capture Groups

June 10, 2014

Regular expressions can be super useful, but they can also be a bit of a pain to work with sometimes. Yesterday I learned about something pretty handy -- a way to tell the regular expression to not capture a group. I've been dealing with captured groups that I do not need captured for years now. Finally, I found an way to remove that nuisance.

Let's begin by considering the following string with a label and a value separated by a colon. However, white space before and after the colon is optional.

Some Header: Sample Value

We want to capture the header text and the value text -- in this example "Some Header" and "Some Value".

So we begin by writing a regular expression


This results in four groups1:

  1. Some Header
  2. nil
  3. Some Value

But really, we don't want to capture the optional white space. It just creates groups we do not want or care about. It may be a nuisance, but it is also a nuisance that we can circumvent. The ?: option inside of a group tells the regex parser to not capture the group. How convenient! So now let's modify our regex.


Now we have only the results we care about1:

  1. Some Header
  2. Some Value

This is a pretty convenient regex option that I plan on using often going forward.

  1. Note: For simplicity I intentionally left out the actual first group in the result -- the full string.