From: Robert Klemme <bob.news@...>
Date: 2006-03-29T05:58:55+09:00
Subject: Re: Regexp to match strings that _don't_ being with a string

Wes Gamble wrote:
> Thanks, that makes sense since the lookahead doesn't "consume" right?

Right.  In this case an alternation works, too:

p %w{abcd xyz as}.map {|s| /^(?!abc|xyz)/=~s}
=> [nil, nil, 0]

De Morgan's Law comes to mind: not a and not b <=> not(a or b) :-)

Kind regards

	robert

> WG
> Joel VanderWerf wrote:
>> Wes Gamble wrote:
>>> I have a new wrinkle.
>>>
>>> Now I want to match any line that doesn't have "xyz" or "abc" at the 
>>> beginning of the line.
>>>
>>> Is there a way to "AND" together the input to the negative lookahead 
>>> assertion?
>> For lookaheads, you can get AND by concatenating:
>>
>>
>> irb(main):001:0> /^(?!abc)(?!xyz)/ =~ "abc"
>> => nil
>> irb(main):002:0> /^(?!abc)(?!xyz)/ =~ " abc"
>> => 0
>> irb(main):003:0> /^(?!abc)(?!xyz)/ =~ "xyz"
>> => nil
>> irb(main):004:0> /^(?!abc)(?!xyz)/ =~ " xyz"
>> => 0
> 
>