From: Steve Throckmorton <nntp.m.ttwelve@...>
Date: 2006-07-18T02:50:04+09:00
Subject: Re: mystery regexp

There ya go.  Thanks.


gregarican wrote:

> Check out http://www.zenspider.com/Languages/Ruby/QuickRef.html#11 for
> details on this portion of the regex. It seems to involve look-ahead
> capability.
> 
> HTH.
> 
> Steve Throckmorton wrote:
> 
>>I found this regexp in the docs for the OptionParser class, and I don't
>>understand it.  Google hasn't helped, nor has the Pickaxe, so I thought
>>I would ask here.  The purpose of the code is to ensure that a file
>>extension submitted by the user begins with a period (a dot).
>>
>>file_ext.sub!(/\A\.(?=.)/, ".")
>>
>>I understand all except (?=.)  As far as I can tell the regexp works
>>fine without it.  I can delete the dot inside the parens, and the code
>>still runs.  I can change the = to a - and the code runs, but if I
>>substitute a letter or a * instead, it doesn't.
>>
>>Someone please clue me in here.  What is this thing?
> 
>