great, thanks for the answer ;-) 2009/6/3 Wu JIANG <albert.w.ji...@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 <uai...@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.ji...@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 <uai...@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
