regex - How do I make part of a regular expression optional in Ruby?

Question

To match the following:

On Mar 3, 2011 11:05 AM, "mr person" 
wrote: 

I have the following regular expression:

/(On.* (?:Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec) d{1,2}, [12]d{3}.* at d{1,2}:d{1,2} (?:AM|PM),.*wrote:)/m

Is there a way to make the at optional? so if it's there great, if not, it still matches?

Answer 1

Sure. Put it in parentheses, put a question mark after it. Include one of the spaces (since otherwise you'll be trying to match two spaces if the "at" is missing.) (at )? (or as someone else suggested, (?:at )? to avoid it being captured).