Re: [9fans] plan 9 regexp

[hugo rivera <uair00@gmail.com>]

great, thanks for the answer ;-)

2009/6/3 Wu JIANG <albert.w.jiang@gmail.com>:
> Sorry, I misunderstood your question in the first place. I think one example
> can be good to show how ``?'' is useful somehow in grep.
>
> Suppose I have a file, I want to find out a keyword ``produce'', but I know
> that the word ``produced'' might also be the word that I am interested (stem
> process in information retrieval or nlp). So I use the pattern "produced?"
> to find all the words useful to me.
>
> I hope this can be helpful at least a little bit. :-)
>
> On Wed, Jun 3, 2009 at 4:11 PM, hugo rivera <uair00@gmail.com> wrote:
>>
>> you are right, but the original post read
>>
>> > grep 'a+bb?'
>>
>> so you get at least one 'a' and one or two 'b'.
>>
>> 2009/6/3 Wu JIANG <albert.w.jiang@gmail.com>:
>> > actually, a+ means at least one 'a', b? means zero or one 'b'.
>> >
>> > On Wed, Jun 3, 2009 at 10:56 AM, hugo rivera <uair00@gmail.com> wrote:
>> >>
>> >> Hello,
>> >> I am experimenting with some regexp implementations (namely the one
>> >> from "the practice of programming") and I am a little disoriented by
>> >> the use of the '?' operator in plan 9's grep:
>> >> say I have the following input
>> >>
>> >> aaaabbb
>> >> ab
>> >> aaaab
>> >> bb
>> >> b
>> >> aaabb
>> >> aaaa
>> >>
>> >> which I feed into grep with
>> >>
>> >> grep 'a+bb?'
>> >>
>> >> which should match at least one 'a' followed by one or two 'b'. So,
>> >> grep's output is
>> >>
>> >> aaaabbb
>> >> ab
>> >> aaaab
>> >> aaabb
>> >>
>> >> which really surprised me at first, since I wasn't expecting the first
>> >> line. After some thought, I realized that the 'aaaab' and the 'aaaabb'
>> >> patterns, contained in the first line of input, match the regexp, so
>> >> grep prints the line.
>> >> But then, how exactly the '?' operator is useful for grep? I was
>> >> thinking that it was good to filter lines that contain more characters
>> >> that desired, but it is not.
>> >> Saludos
>> >> --
>> >> Hugo
>> >>
>> >
>> >
>>
>>
>>
>> --
>> Hugo
>>
>
>



--
Hugo