[erlang-questions] run strange behaviour

[Vyacheslav Levytskyy]

Hello,

According to 're' module documentation, "the quantifiers are "greedy", 
that is, they match as much as possible (up to the maximum number of 
permitted times)". This seems to be a problem with your case. The regex 
you are using seems a bit problematic, forcing 're' to exhausting 
repetitions.

As an option, you can use 'ungreedy' option, making only some of 
quantifiers greedy via following them by "?". See for example:
re:run(<<"foo bar is a foo bar is a big yellow boat or sub">>, <<"^foo 
(\\w(\\w+| )*) is a (\\w(\\w+?| )*?)">>, [ungreedy, global, {capture, 
[1,3], binary}]).
{match,[[<<"bar">>,
          <<"foo bar is a big yellow boat or sub">>]]}

Best regards,
Vyacheslav Levytskyy

On 23.10.2013 22:26, Alexander Petrovsky wrote:
> Hi!
>
> I have the regex "^foo (\\w+(\\w* *)*) is an (\\w+(\\w* *)*)", and I 
> get strange behaviour when I do:
>
> 1> re:run(<<"foo bar is a foo bar is a big yellow boat or">>, <<"^foo 
> (\\w+(\\w* *)*) is a (\\w+(\\w* *)*)">>, [global, {capture, [1,3], 
> binary}]).
> {match,[[<<"bar is a foo bar">>,<<"big yellow boat or">>]]}
>
> 2> re:run(<<"foo bar is a foo bar is a big yellow boat or sub">>, 
> <<"^foo (\\w+(\\w* *)*) is a (\\w+(\\w* *)*)">>, [global, {capture, 
> [1,3], binary}]).
> nomatch
>
> I tested this regexp in clojure and python:
>
> => (re-matches #"foo (\w+(\w* *)*) is a (\w+(\w* *)*)" "foo bar is a 
> foo bar is a big yellow boat or")
> ["foo bar is a foo bar is a big yellow boat or" "bar is a foo bar" "" 
> "big yellow boat or" ""]
>
> => (re-matches #"foo (\w+(\w* *)*) is a (\w+(\w* *)*)" "foo bar is a 
> foo bar is a big yellow boat or sub")
> ["foo bar is a foo bar is a big yellow boat or sub" "bar is a foo bar" 
> "" "big yellow boat or sub" ""]
>
> >>> import re
> >>> p = re.compile('foo (\w+(\w* *)*) is a (\w+(\w* *)*)')
> >>> p.match("foo bar is a foo bar is a big yellow boat or")
> <_sre.SRE_Match object at 0x100293c00>
> >>> p.match("foo bar is a foo bar is a big yellow boat or sub")
> <_sre.SRE_Match object at 0x100293ab0>
>
> Can someone explain me, why I get on second string "foo bar is a foo 
> bar is a big yellow boat or sub" nomatch? This is a bug?
>
>
> -- 
> ?????????? ????????? / Alexander Petrovsky,
>
> Skype: askjuise
> Jabber: juise@REDACTED <mailto:juise@REDACTED>
> Phone: +7 914 8 820 815 (irkutsk)
>
>
>
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