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Re: \W and underscore

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  • flo.gehrke
    ... What about the POSIX Character Class [[:alnum:]] ? It matches numbers and letters (including characters with diacritics) but not the underscore. ... It s
    Message 1 of 15 , Mar 16, 2013
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      --- In ntb-clips@yahoogroups.com, "John Shotsky" <jshotsky@...> wrote:
      >
      > Yet again, I've learned the hard way that \w, which is supposed
      > to mean letters and numbers, includes the underscore [_],(...)
      > This presents a bit of a problem when one uses \w virtually
      > everywhere expecting it to only pertain to actual letters and
      > numbers.

      What about the POSIX Character Class '[[:alnum:]]'? It matches numbers and letters (including characters with diacritics) but not the underscore.

      > I DO hope the developers of PCRE will address this problem.

      It's a rule that goes back to the history of Perl. So, probably, the PCRE developers won't feel affected by this issue.

      Flo
    • John Shotsky
      No, [^ w_]+ will collect line ends too. You need to use [^ w_ r n]+ to prevent it. Regards, John RecipeTools Web Site:
      Message 2 of 15 , Mar 16, 2013
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        No, [^\w_]+ will collect line ends too. You need to use [^\w_\r\n]+ to prevent it.

        Regards,
        John
        RecipeTools Web Site: <http://recipetools.gotdns.com/> http://recipetools.gotdns.com/
        John's Mags Yahoo Group: <http://groups.yahoo.com/group/johnsmags/> http://groups.yahoo.com/group/johnsmags/

        From: ntb-clips@yahoogroups.com [mailto:ntb-clips@yahoogroups.com] On Behalf Of Axel Berger
        Sent: Saturday, March 16, 2013 20:11
        To: ntb-clips@yahoogroups.com
        Subject: Re: [Clip] \W and underscore


        John Shotsky wrote:
        > you have to include \r\n in the negative class

        I don't see why. \w and \W are complemetary, so \w and [^\W] should be
        exactly the same. So if what you're looking for is "\w except _" and "\W
        plus _" [\W_] and [^\W_] are your two solutions.
        Or are those line ends another problem on top of the _ one? If so it
        will have to be tackled too of course.

        Axel



        [Non-text portions of this message have been removed]
      • Axel Berger
        ... Yes, it s wrong. w (small letter) already includes _, so [^ w_] and [^ w] are identical. It s W (big letter) that you need to add the _ to. Axel
        Message 3 of 15 , Mar 16, 2013
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          John Shotsky wrote:
          > No, [^\w_]

          Yes, it's wrong. \w (small letter) already includes _, so [^\w_] and
          [^\w] are identical. It's \W (big letter) that you need to add the _ to.

          Axel
        • John Shotsky
          I would rather rename all underscores in the beginning to avoid this problem than have to convert my whole library to use that nomenclature when all I want is
          Message 4 of 15 , Mar 16, 2013
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            I would rather rename all underscores in the beginning to avoid this problem than have to convert my whole library to use that
            nomenclature when all I want is for \w to work as it should. For example, I could convert the underscores to [_] (including the
            brackets) and then all would work as expected.

            PCRE and Perl are already different, I would rather see this cleared up than leave it in place because, uh, that's the way we've
            always done it.

            Regards,
            John
            RecipeTools Web Site: <http://recipetools.gotdns.com/> http://recipetools.gotdns.com/
            John's Mags Yahoo Group: <http://groups.yahoo.com/group/johnsmags/> http://groups.yahoo.com/group/johnsmags/

            From: ntb-clips@yahoogroups.com [mailto:ntb-clips@yahoogroups.com] On Behalf Of flo.gehrke
            Sent: Saturday, March 16, 2013 20:18
            To: ntb-clips@yahoogroups.com
            Subject: [Clip] Re: \W and underscore


            --- In ntb-clips@yahoogroups.com <mailto:ntb-clips%40yahoogroups.com> , "John Shotsky" <jshotsky@...> wrote:
            >
            > Yet again, I've learned the hard way that \w, which is supposed
            > to mean letters and numbers, includes the underscore [_],(...)
            > This presents a bit of a problem when one uses \w virtually
            > everywhere expecting it to only pertain to actual letters and
            > numbers.

            What about the POSIX Character Class '[[:alnum:]]'? It matches numbers and letters (including characters with diacritics) but not
            the underscore.

            > I DO hope the developers of PCRE will address this problem.

            It's a rule that goes back to the history of Perl. So, probably, the PCRE developers won't feel affected by this issue.

            Flo



            [Non-text portions of this message have been removed]
          • flo.gehrke
            ... That s not quite correct. With POSIX Character Classes, you can combine positive and negative definitions to some extent. Example: [0[:^digit:]] will
            Message 5 of 15 , Mar 16, 2013
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              --- In ntb-clips@yahoogroups.com, Axel Berger <Axel-Berger@...> wrote:
              >
              > By the way I just reread the help. A class can either be all
              > positive or all negative...

              That's not quite correct. With POSIX Character Classes, you can combine positive and negative definitions to some extent.

              Example: '[0[:^digit:]]' will match zero and any character that is no digit.

              Flo
            • John Shotsky
              That is useful. I will have to document that for myself. I have a clip called my notes in which I keep all these gems. That s where I noticed this original
              Message 6 of 15 , Mar 16, 2013
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                That is useful. I will have to document that for myself. I have a clip called 'my notes' in which I keep all these gems. That's
                where I noticed this original problem was already documented. Duh.

                Regards,
                John
                RecipeTools Web Site: <http://recipetools.gotdns.com/> http://recipetools.gotdns.com/
                John's Mags Yahoo Group: <http://groups.yahoo.com/group/johnsmags/> http://groups.yahoo.com/group/johnsmags/

                From: ntb-clips@yahoogroups.com [mailto:ntb-clips@yahoogroups.com] On Behalf Of flo.gehrke
                Sent: Saturday, March 16, 2013 20:43
                To: ntb-clips@yahoogroups.com
                Subject: Re: [Clip] \W and underscore


                --- In ntb-clips@yahoogroups.com <mailto:ntb-clips%40yahoogroups.com> , Axel Berger <Axel-Berger@...> wrote:
                >
                > By the way I just reread the help. A class can either be all
                > positive or all negative...

                That's not quite correct. With POSIX Character Classes, you can combine positive and negative definitions to some extent.

                Example: '[0[:^digit:]]' will match zero and any character that is no digit.

                Flo



                [Non-text portions of this message have been removed]
              • Don
                I think it should be as is. A _ is not a word boundary ... it is used to join the words. As Flo points out, they gave you a solution and as Axel points out
                Message 7 of 15 , Mar 16, 2013
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                  I think it should be as is. A _ is not a word boundary ... it is used
                  to join the words.

                  As Flo points out, they gave you a solution and as Axel points out there
                  is another easy solution. If they happened to conclude that you were
                  right, that would require all manner of recoding ... which is what you
                  are disinclined to do here for your libraries apparently and yet the
                  entire world would have to do so if your thought carries the day.

                  I'd say it matters not what we think, because as Flo says, it has roots
                  in Perl.


                  On 3/16/2013 11:26 PM, John Shotsky wrote:
                  > I would rather rename all underscores in the beginning to avoid this problem than have to convert my whole library to use that
                  > nomenclature when all I want is for \w to work as it should. For example, I could convert the underscores to [_] (including the
                  > brackets) and then all would work as expected.
                  >
                • John Shotsky
                  Yet it works with b as a word boundary. If it is treated as a word boundary, it is NOT being treated as a letter or number in THAT case. That is, a b detects
                  Message 8 of 15 , Mar 16, 2013
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                    Yet it works with \b as a word boundary. If it is treated as a word boundary, it is NOT being treated as a letter or number in THAT
                    case. That is, a \b detects that a word ends, but \w includes the [_]. I don't care about history � PCRE is already different than
                    Perl. It is not selfish to think that \w, which is defined as all letters and numbers, should actually BE all numbers and letters
                    AND NOT the underscore. Nowhere else, in all of PCRE (as far as I know) does a non-letter and non-number count as a letter or a
                    number. That is just wrong.

                    Regards,
                    John
                    RecipeTools Web Site: <http://recipetools.gotdns.com/> http://recipetools.gotdns.com/
                    John's Mags Yahoo Group: <http://groups.yahoo.com/group/johnsmags/> http://groups.yahoo.com/group/johnsmags/

                    From: ntb-clips@yahoogroups.com [mailto:ntb-clips@yahoogroups.com] On Behalf Of Don
                    Sent: Saturday, March 16, 2013 21:00
                    To: ntb-clips@yahoogroups.com
                    Subject: Re: [Clip] Re: \W and underscore


                    I think it should be as is. A _ is not a word boundary ... it is used
                    to join the words.

                    As Flo points out, they gave you a solution and as Axel points out there
                    is another easy solution. If they happened to conclude that you were
                    right, that would require all manner of recoding ... which is what you
                    are disinclined to do here for your libraries apparently and yet the
                    entire world would have to do so if your thought carries the day.

                    I'd say it matters not what we think, because as Flo says, it has roots
                    in Perl.

                    On 3/16/2013 11:26 PM, John Shotsky wrote:
                    > I would rather rename all underscores in the beginning to avoid this problem than have to convert my whole library to use that
                    > nomenclature when all I want is for \w to work as it should. For example, I could convert the underscores to [_] (including the
                    > brackets) and then all would work as expected.
                    >



                    [Non-text portions of this message have been removed]
                  • flo.gehrke
                    ... This is misleading. A single character like the underscore can never be represent a word boundary. b is an assertion that matches at a position where a
                    Message 9 of 15 , Mar 16, 2013
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                      --- In ntb-clips@yahoogroups.com, "John Shotsky" <jshotsky@...> wrote:
                      >
                      > This also complicates the use of \b for word boundaries,
                      > because \b DOES treat this character as a word boundary.

                      This is misleading. A single character like the underscore can never be represent a word boundary. '\b' is an assertion that matches at a position where a non-word character is preceded resp. followed by a word character. Thus it signifies a position of zero length and no single character.

                      As discussed here, the underscore is defined as a normal word character. So '\bJohn' doesn't match the string 'aaa _John', for example, because 'John' is not preceded by a word boundary in this case.

                      Flo
                    • Axel Berger
                      ... You re absolutely right. I had taken John by his word and not tested this. In the text aaabbbccc aaa bbbccc aaabbb ccc aaa bbb ccc aaa_bbbccc aaabbb_ccc
                      Message 10 of 15 , Mar 16, 2013
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                        "flo.gehrke" wrote:
                        > As discussed here, the underscore is defined as a normal word character.

                        You're absolutely right. I had taken John by his word and not tested
                        this.

                        In the text

                        aaabbbccc
                        aaa bbbccc aaabbb ccc aaa bbb ccc
                        aaa_bbbccc aaabbb_ccc aaa_bbb_ccc
                        aaa _bbb ccc aaa bbb_ ccc aaa _bbb_ ccc
                        aaa_ bbb_ccc aaa_bbb _ccc aaa_ bbb _ccc

                        the pattern "\bbbb\b" (b was a bad letter choice in hindsight) matches
                        the last string in the second and in the fifth line, nothing else.

                        Axel
                      • John Shotsky
                        You re right, I was not paying attention. It was selecting the last character, which was the underscore and the boundary was the following character. If you do
                        Message 11 of 15 , Mar 17, 2013
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                          You're right, I was not paying attention. It was selecting the last character, which was the underscore and the boundary was the
                          following character. If you do your test with a space following the underscore, you will see what I mean.

                          Regards,
                          John
                          RecipeTools Web Site: <http://recipetools.gotdns.com/> http://recipetools.gotdns.com/
                          John's Mags Yahoo Group: <http://groups.yahoo.com/group/johnsmags/> http://groups.yahoo.com/group/johnsmags/

                          From: ntb-clips@yahoogroups.com [mailto:ntb-clips@yahoogroups.com] On Behalf Of Axel Berger
                          Sent: Saturday, March 16, 2013 23:51
                          To: ntb-clips@yahoogroups.com
                          Subject: Re: [Clip] Re: \W and underscore


                          "flo.gehrke" wrote:
                          > As discussed here, the underscore is defined as a normal word character.

                          You're absolutely right. I had taken John by his word and not tested
                          this.

                          In the text

                          aaabbbccc
                          aaa bbbccc aaabbb ccc aaa bbb ccc
                          aaa_bbbccc aaabbb_ccc aaa_bbb_ccc
                          aaa _bbb ccc aaa bbb_ ccc aaa _bbb_ ccc
                          aaa_ bbb_ccc aaa_bbb _ccc aaa_ bbb _ccc

                          the pattern "\bbbb\b" (b was a bad letter choice in hindsight) matches
                          the last string in the second and in the fifth line, nothing else.

                          Axel



                          [Non-text portions of this message have been removed]
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