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Re: [perl #109206] regexes: . different from [^\n]

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From:
demerphq
Date:
January 28, 2012 13:27
Subject:
Re: [perl #109206] regexes: . different from [^\n]
Message ID:
CANgJU+UKPDiSf7y1PioSGdQkhQsRgKJ3Okq3Je4PGeb7qWFUZg@mail.gmail.com
On 28 January 2012 19:30, Lukas Mai <l.mai@web.de> wrote:
> On 2012-01-28 demerphq wrote:
>
>> You say that you consider "\n" to contain only one line.
>>
>> But what about "\nfoo". Does it contain one or two lines? Do you
>> expect ^ to match after the \n in "\nfoo"? If you do then do you not
>> agree there is an inconsistency about it not matching after the \n in
>> "\n"?
>
> "\nfoo" contains 1.5 lines, i.e. one complete (but empty) line and one
> incomplete (unterminated) line.
> "\nfoo" =~ /^foo/m should match, yes.
> I don't think there's an inconsistency because \n is only the beginning
> of a line if more text follows. That is, my model of /^/m
> is /(?:\A|(?<=\n)(?!\z))/.

And the docs agree with you, perlre says this:

   You may, however, wish to treat a string as a multi-line buffer, such that
   the "^" will match after any newline within the string (except if the newline
   is the last character in the string), and "$" will match before any newline.

Though I do wonder if the "except if the newline  is the last
character of the string" was a special case added later.

>> Because to me that is the exact same thing as expecting /.*/ to match
>> at the end of the string in "\n".
>>
>> So really the bug here is in ^ not in .*
>
> That doesn't match my intuitive understanding of "beginning of line".

It is sort of a lawyers point I guess. To me the definition (start of
string or immediately after a newline) would match up with expecting
/.*/ to match twice against "\n".

Anyway, it sounds like the ANCH_MBOL optimization is buggy, so do we
turn it off or try to fix it somehow...

cheers,
Yves


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

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