Re: [PATCH] gitweb: Better regexp for SHA-1 committag match

[demerphq <demerphq@gmail.com>]

2009/2/7 Jakub Narebski <jnareb@gmail.com>:
> On Sat, 7 Feb 2009, demerphq wrote:
>> 2009/2/6 Jakub Narebski <jnareb@gmail.com>:
>>> Dnia piątek 6. lutego 2009 10:49, Rafael Garcia-Suarez napisał:
>>>> 2009/2/6 Jakub Narebski <jnareb@gmail.com>:
>
>>>>> Make SHA-1 regexp to be turned into hyperlink (the SHA-1 committag)
>>>>> to match word boundary at the beginning and the end.  This way we
>>>>> reduce number of false matches, for example we now don't match
>>>>> 0x74a5cd01 which is hex decimal (for example memory address),
>>>>> but is not SHA-1.
>>>>
>>>> Further suggestion: you could also turn the final \b into (\b|\@),
>>>
>>> You meant \b -> \b(?!\@), didn't you?  Word boundary _not_ followed
>>> by '@', and not word boundary _OR_ '@' as you wrote...
>>
>> Since \b(?!\@) is effectively two zero width negative assertions in a
>> row you could simplify by saying:
>>
>>   (?![^\w\@])
>
> I don't know if "sth\b" is effectively "sth(!?[^\w])"... perhaps it is.

Sorry, my bad, that is double negation, I meant (?![\w\@])

On of the ways you can express \b is as:
(?:(?<=\w)(?!\w)|(?<=\W)(?!\W)|\A)

But the point here is you are looking for the end of a hex sequence,
so you can just use the "end of string" bit of the alternation which
is: (?!\w).

>>
>> and that way you can easily add the '.' case as well.
>
> We cannot add '.' case, because it there can be legitimate SHA-1 match
> ending sentence, e.g.
>
>     ... at commit 8457bb9e.

/(?<!\w)([a-fA-F0-9]+)(?!(?:\.\w|[\w@]))/

:-)

Yves

-- 
perl -Mre=debug -e "/just|another|perl|hacker/"