Re: Problem with a regular expression in Vim

Thanks very much for your detailed explanation.

In fact, by pseudocode I think I can put my requirement like this:

1. Search for the first pair of "==" from the beginning location where
the search starts.
2. Extract the contents in the pair of "==" as the first match result.
3. Disable/Invalidate/Remove the matched contents with its "==" surroundings.
4. Repeat from 1. until reaching the end of the search range.

So, is it possible to do that by regular expression? I'm not very
familiar with the concepts of greedy/non-greedy or zero-match (like
the queer things of \@! or \@<= etc.) or . Will they help?


On Wed, Oct 3, 2012 at 11:41 AM, Ben Fritz <fritzophrenic@gmail.com> wrote:
> On Tuesday, October 2, 2012 9:38:20 PM UTC-5, Xell Liu wrote:
>> Hi all,
>>
>>
>>
>> Suppose this text fragment:
>>
>>
>>
>> xxx==aaa==bbbccc==ddd==yyy
>>
>>
>>
>> How can I match the "aaa" and "ddd" between the pair of "==" without
>>
>> matching the bbbccc (or, of course, "xxx" or "yyy")? Apparently
>>
>> /==\zs[^=]\{-}\ze==/ fails.
>
> For me it matches exactly what you told it to:
>
> ==\zs : after two '=' characters...
> [^=] : match ANY character which is not a '='...
> \{-} : ANY number of times...
> \ze== : until another pair of '=' characters.
>
> In your example, this matches aaa, bbbccc, and ddd. There is no reason I can think of to expect otherwise.
>
>> However /==[^=]\{-}==/ does match the
>>
>> "aaa" and "ddd" WITH the pair of "==". I got lost here.
>>
>>
>
> I'm guessing you noticed that hitting 'n' after searching for this pattern does not match the bbbccc in your example text. This actually surprised me a little, but I think it happens because:
>
> You are searching for the "next" match.
> The beginning of the ==bbbccc== string, which matches your PATTERN, is inside the current match.
> To be useful, the search needs to start AFTER the current match, therefore your pattern is not even tried at this next position.
>
> By setting match end with \ze in your first pattern, you make it so the current match ends BEFORE the ==bbbccc=== string, therefore allowing your pattern to be tried and matched on this text.
>
> Now, how to fix this? Well...that depends on what you actually want. Somebody suggested aaa\|ddd in your pattern, which will certainly match your example text as desired, but I have a feeling the example text is actually not all that similar to what you actually want to match.
>
> In what way are aaa and ddd similar? How do they differ from bbbccc? Is it a matter of number of characters? If so, just replace \{-} with \{3} to match exactly three characters, or \{1,3} for 1-3 characters, or \{0,3} to more closely match what you have now. Or are you actually looking for a literal aaa or ddd?
>
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