php regex: Alternative to backreference in negative lookbehind












5














I want to find instances where a captured group does not appear later in the string:



aaaBbb  = CccBbb  <- format is valid, skip

aaaDddd = CccDddd <- format is valid, skip

aaaEeee = CccFfff <- format is not valid, match this one only


So this matches the lines I don't want to match ( https://regex101.com/r/lon87L/1 )



/^ +w+([A-Z][a-z+]) += +w+1$/mg


I've read on https://www.regular-expressions.info/refadv.html that php doesn't support backreferences inside a negative lookbehind, but other implementations of regex can. So something like this would match the invalid lines that I want to match, but it doesn't work in php:



/^ +w+([A-Z][a-z+]) += +w+(?<!1)$/mg


Is there anything else that would work, other than matching all of three lines and looping through the matches in a php foreach?






php regex negative-lookbehind







share|improve this question






















  • Negative lookbehinds require a compile time fixed length. A backreference is a runtime item with variable length. One option is to (?>1(*SKIP)(*FAIL)|w)+ and match the backreference. This is probably quicker too.
    – sln
    Nov 15 at 22:19










  • You can see it here regex101.com/r/6gfSBi/1 Btw, only the Dot-Net engine supports variable width lookbehinds (including backreferences).
    – sln
    Nov 15 at 22:22












  • If it has to be at the EOS, just add a $ after the backref regex101.com/r/QuXJLY/1
    – sln
    Nov 15 at 22:27
















5














I want to find instances where a captured group does not appear later in the string:



aaaBbb  = CccBbb  <- format is valid, skip

aaaDddd = CccDddd <- format is valid, skip

aaaEeee = CccFfff <- format is not valid, match this one only


So this matches the lines I don't want to match ( https://regex101.com/r/lon87L/1 )



/^ +w+([A-Z][a-z+]) += +w+1$/mg


I've read on https://www.regular-expressions.info/refadv.html that php doesn't support backreferences inside a negative lookbehind, but other implementations of regex can. So something like this would match the invalid lines that I want to match, but it doesn't work in php:



/^ +w+([A-Z][a-z+]) += +w+(?<!1)$/mg


Is there anything else that would work, other than matching all of three lines and looping through the matches in a php foreach?






php regex negative-lookbehind







share|improve this question






















  • Negative lookbehinds require a compile time fixed length. A backreference is a runtime item with variable length. One option is to (?>1(*SKIP)(*FAIL)|w)+ and match the backreference. This is probably quicker too.
    – sln
    Nov 15 at 22:19










  • You can see it here regex101.com/r/6gfSBi/1 Btw, only the Dot-Net engine supports variable width lookbehinds (including backreferences).
    – sln
    Nov 15 at 22:22












  • If it has to be at the EOS, just add a $ after the backref regex101.com/r/QuXJLY/1
    – sln
    Nov 15 at 22:27














5












5








5


1





I want to find instances where a captured group does not appear later in the string:



aaaBbb  = CccBbb  <- format is valid, skip

aaaDddd = CccDddd <- format is valid, skip

aaaEeee = CccFfff <- format is not valid, match this one only


So this matches the lines I don't want to match ( https://regex101.com/r/lon87L/1 )



/^ +w+([A-Z][a-z+]) += +w+1$/mg


I've read on https://www.regular-expressions.info/refadv.html that php doesn't support backreferences inside a negative lookbehind, but other implementations of regex can. So something like this would match the invalid lines that I want to match, but it doesn't work in php:



/^ +w+([A-Z][a-z+]) += +w+(?<!1)$/mg


Is there anything else that would work, other than matching all of three lines and looping through the matches in a php foreach?






php regex negative-lookbehind







share|improve this question













I want to find instances where a captured group does not appear later in the string:



aaaBbb  = CccBbb  <- format is valid, skip

aaaDddd = CccDddd <- format is valid, skip

aaaEeee = CccFfff <- format is not valid, match this one only


So this matches the lines I don't want to match ( https://regex101.com/r/lon87L/1 )



/^ +w+([A-Z][a-z+]) += +w+1$/mg


I've read on https://www.regular-expressions.info/refadv.html that php doesn't support backreferences inside a negative lookbehind, but other implementations of regex can. So something like this would match the invalid lines that I want to match, but it doesn't work in php:



/^ +w+([A-Z][a-z+]) += +w+(?<!1)$/mg


Is there anything else that would work, other than matching all of three lines and looping through the matches in a php foreach?






php regex negative-lookbehind




php regex negative-lookbehind






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked Nov 15 at 22:00









Redzarf

1,3211731




1,3211731












  • Negative lookbehinds require a compile time fixed length. A backreference is a runtime item with variable length. One option is to (?>1(*SKIP)(*FAIL)|w)+ and match the backreference. This is probably quicker too.
    – sln
    Nov 15 at 22:19










  • You can see it here regex101.com/r/6gfSBi/1 Btw, only the Dot-Net engine supports variable width lookbehinds (including backreferences).
    – sln
    Nov 15 at 22:22












  • If it has to be at the EOS, just add a $ after the backref regex101.com/r/QuXJLY/1
    – sln
    Nov 15 at 22:27


















  • Negative lookbehinds require a compile time fixed length. A backreference is a runtime item with variable length. One option is to (?>1(*SKIP)(*FAIL)|w)+ and match the backreference. This is probably quicker too.
    – sln
    Nov 15 at 22:19










  • You can see it here regex101.com/r/6gfSBi/1 Btw, only the Dot-Net engine supports variable width lookbehinds (including backreferences).
    – sln
    Nov 15 at 22:22












  • If it has to be at the EOS, just add a $ after the backref regex101.com/r/QuXJLY/1
    – sln
    Nov 15 at 22:27
















Negative lookbehinds require a compile time fixed length. A backreference is a runtime item with variable length. One option is to (?>1(*SKIP)(*FAIL)|w)+ and match the backreference. This is probably quicker too.
– sln
Nov 15 at 22:19




Negative lookbehinds require a compile time fixed length. A backreference is a runtime item with variable length. One option is to (?>1(*SKIP)(*FAIL)|w)+ and match the backreference. This is probably quicker too.
– sln
Nov 15 at 22:19












You can see it here regex101.com/r/6gfSBi/1 Btw, only the Dot-Net engine supports variable width lookbehinds (including backreferences).
– sln
Nov 15 at 22:22






You can see it here regex101.com/r/6gfSBi/1 Btw, only the Dot-Net engine supports variable width lookbehinds (including backreferences).
– sln
Nov 15 at 22:22














If it has to be at the EOS, just add a $ after the backref regex101.com/r/QuXJLY/1
– sln
Nov 15 at 22:27




If it has to be at the EOS, just add a $ after the backref regex101.com/r/QuXJLY/1
– sln
Nov 15 at 22:27












2 Answers
2






active

oldest

votes


















2














Try using using a negative lookahead instead of a negative lookbehind. It works equally well, plus it works in PHP.



^ +w+([A-Z][a-z]+) += +(?!w+1).*$


regex101 demo



PHP demo






share|improve this answer































    1














    One option would be to, right before each repeated w after the =, use negative lookahead for 1$:



    ^ +w+([A-Z][a-z]+) += +(?:(?!1$)w)+$
    
                        ^^^^^^^^^^^^^^


    https://regex101.com/r/lon87L/2



    But that only excludes a match if the backreference occurs right at the end of the string. If you want to ensure that the previously matched phrase doesn't occur anywhere within the final ws, just remove the $ from inside the repeated group:



    ^ +w+([A-Z][a-z]+) += +(?:(?!1)w)+$
    
                                ^


    https://regex101.com/r/lon87L/3






    share|improve this answer





















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      2 Answers
      2






      active

      oldest

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      2 Answers
      2






      active

      oldest

      votes









      active

      oldest

      votes






      active

      oldest

      votes









      2














      Try using using a negative lookahead instead of a negative lookbehind. It works equally well, plus it works in PHP.



      ^ +w+([A-Z][a-z]+) += +(?!w+1).*$


      regex101 demo



      PHP demo






      share|improve this answer




























        2














        Try using using a negative lookahead instead of a negative lookbehind. It works equally well, plus it works in PHP.



        ^ +w+([A-Z][a-z]+) += +(?!w+1).*$


        regex101 demo



        PHP demo






        share|improve this answer


























          2












          2








          2






          Try using using a negative lookahead instead of a negative lookbehind. It works equally well, plus it works in PHP.



          ^ +w+([A-Z][a-z]+) += +(?!w+1).*$


          regex101 demo



          PHP demo






          share|improve this answer














          Try using using a negative lookahead instead of a negative lookbehind. It works equally well, plus it works in PHP.



          ^ +w+([A-Z][a-z]+) += +(?!w+1).*$


          regex101 demo



          PHP demo







          share|improve this answer














          share|improve this answer



          share|improve this answer








          edited Nov 15 at 22:45

























          answered Nov 15 at 22:29









          Davіd

          3,62541635




          3,62541635

























              1














              One option would be to, right before each repeated w after the =, use negative lookahead for 1$:



              ^ +w+([A-Z][a-z]+) += +(?:(?!1$)w)+$
              
                        ^^^^^^^^^^^^^^


              https://regex101.com/r/lon87L/2



              But that only excludes a match if the backreference occurs right at the end of the string. If you want to ensure that the previously matched phrase doesn't occur anywhere within the final ws, just remove the $ from inside the repeated group:



              ^ +w+([A-Z][a-z]+) += +(?:(?!1)w)+$
              
                                ^


              https://regex101.com/r/lon87L/3






              share|improve this answer


























                1














                One option would be to, right before each repeated w after the =, use negative lookahead for 1$:



                ^ +w+([A-Z][a-z]+) += +(?:(?!1$)w)+$
                
                        ^^^^^^^^^^^^^^


                https://regex101.com/r/lon87L/2



                But that only excludes a match if the backreference occurs right at the end of the string. If you want to ensure that the previously matched phrase doesn't occur anywhere within the final ws, just remove the $ from inside the repeated group:



                ^ +w+([A-Z][a-z]+) += +(?:(?!1)w)+$
                
                                ^


                https://regex101.com/r/lon87L/3






                share|improve this answer
























                  1












                  1








                  1






                  One option would be to, right before each repeated w after the =, use negative lookahead for 1$:



                  ^ +w+([A-Z][a-z]+) += +(?:(?!1$)w)+$
                  
                        ^^^^^^^^^^^^^^


                  https://regex101.com/r/lon87L/2



                  But that only excludes a match if the backreference occurs right at the end of the string. If you want to ensure that the previously matched phrase doesn't occur anywhere within the final ws, just remove the $ from inside the repeated group:



                  ^ +w+([A-Z][a-z]+) += +(?:(?!1)w)+$
                  
                                ^


                  https://regex101.com/r/lon87L/3






                  share|improve this answer












                  One option would be to, right before each repeated w after the =, use negative lookahead for 1$:



                  ^ +w+([A-Z][a-z]+) += +(?:(?!1$)w)+$
                  
                        ^^^^^^^^^^^^^^


                  https://regex101.com/r/lon87L/2



                  But that only excludes a match if the backreference occurs right at the end of the string. If you want to ensure that the previously matched phrase doesn't occur anywhere within the final ws, just remove the $ from inside the repeated group:



                  ^ +w+([A-Z][a-z]+) += +(?:(?!1)w)+$
                  
                                ^


                  https://regex101.com/r/lon87L/3







                  share|improve this answer












                  share|improve this answer



                  share|improve this answer










                  answered Nov 15 at 22:07









                  CertainPerformance

                  75.1k143659




                  75.1k143659






























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