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Re: [Clip] \W and underscore

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  • Axel Berger
    ... 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 _
    Message 1 of 15 , Mar 16, 2013
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      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
    • 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 2 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 3 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 4 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 5 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 6 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 7 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 8 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 9 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 10 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 11 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 12 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



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