Regular expressions: Ensuring b doesn't come between a and c












13















Here's something I'm trying to do with regular expressions, and I can't figure out how. I have a big file, and strings abc, 123 and xyz that appear multiple times throughout the file.



I want a regular expression to match a substring of the big file that begins with abc, contains 123 somewhere in the middle, ends with xyz, and there are no other instances of abc or xyz in the substring besides the start and the end.



Is this possible with regular expressions?






regex python-2.7







share|improve this question




















  • 5





    Since regular expressions are not fully standardized, all questions with this tag should also include a tag specifying the applicable programming language or tool. That said, is there any particular reason you want to use regular expressions here? It's possible, but in most environments, it's more complicated than not using regexes.

    – user743382
    May 15 '16 at 15:56











  • Should line breaks be considered or not? The big file will be read line by line or as one big string?

    – Jorge Campos
    May 15 '16 at 15:59











  • Regex flavor is python 2.7, newlines should be included.

    – Ram Rachum
    May 15 '16 at 16:16
















13















Here's something I'm trying to do with regular expressions, and I can't figure out how. I have a big file, and strings abc, 123 and xyz that appear multiple times throughout the file.



I want a regular expression to match a substring of the big file that begins with abc, contains 123 somewhere in the middle, ends with xyz, and there are no other instances of abc or xyz in the substring besides the start and the end.



Is this possible with regular expressions?






regex python-2.7







share|improve this question




















  • 5





    Since regular expressions are not fully standardized, all questions with this tag should also include a tag specifying the applicable programming language or tool. That said, is there any particular reason you want to use regular expressions here? It's possible, but in most environments, it's more complicated than not using regexes.

    – user743382
    May 15 '16 at 15:56











  • Should line breaks be considered or not? The big file will be read line by line or as one big string?

    – Jorge Campos
    May 15 '16 at 15:59











  • Regex flavor is python 2.7, newlines should be included.

    – Ram Rachum
    May 15 '16 at 16:16














13












13








13


8






Here's something I'm trying to do with regular expressions, and I can't figure out how. I have a big file, and strings abc, 123 and xyz that appear multiple times throughout the file.



I want a regular expression to match a substring of the big file that begins with abc, contains 123 somewhere in the middle, ends with xyz, and there are no other instances of abc or xyz in the substring besides the start and the end.



Is this possible with regular expressions?






regex python-2.7







share|improve this question
















Here's something I'm trying to do with regular expressions, and I can't figure out how. I have a big file, and strings abc, 123 and xyz that appear multiple times throughout the file.



I want a regular expression to match a substring of the big file that begins with abc, contains 123 somewhere in the middle, ends with xyz, and there are no other instances of abc or xyz in the substring besides the start and the end.



Is this possible with regular expressions?






regex python-2.7




regex python-2.7






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited May 15 '16 at 16:16









Jorge Campos

17.1k63766




17.1k63766










asked May 15 '16 at 15:53









Ram RachumRam Rachum

25.7k61183300




25.7k61183300








  • 5





    Since regular expressions are not fully standardized, all questions with this tag should also include a tag specifying the applicable programming language or tool. That said, is there any particular reason you want to use regular expressions here? It's possible, but in most environments, it's more complicated than not using regexes.

    – user743382
    May 15 '16 at 15:56











  • Should line breaks be considered or not? The big file will be read line by line or as one big string?

    – Jorge Campos
    May 15 '16 at 15:59











  • Regex flavor is python 2.7, newlines should be included.

    – Ram Rachum
    May 15 '16 at 16:16














  • 5





    Since regular expressions are not fully standardized, all questions with this tag should also include a tag specifying the applicable programming language or tool. That said, is there any particular reason you want to use regular expressions here? It's possible, but in most environments, it's more complicated than not using regexes.

    – user743382
    May 15 '16 at 15:56











  • Should line breaks be considered or not? The big file will be read line by line or as one big string?

    – Jorge Campos
    May 15 '16 at 15:59











  • Regex flavor is python 2.7, newlines should be included.

    – Ram Rachum
    May 15 '16 at 16:16








5




5





Since regular expressions are not fully standardized, all questions with this tag should also include a tag specifying the applicable programming language or tool. That said, is there any particular reason you want to use regular expressions here? It's possible, but in most environments, it's more complicated than not using regexes.

– user743382
May 15 '16 at 15:56





Since regular expressions are not fully standardized, all questions with this tag should also include a tag specifying the applicable programming language or tool. That said, is there any particular reason you want to use regular expressions here? It's possible, but in most environments, it's more complicated than not using regexes.

– user743382
May 15 '16 at 15:56













Should line breaks be considered or not? The big file will be read line by line or as one big string?

– Jorge Campos
May 15 '16 at 15:59





Should line breaks be considered or not? The big file will be read line by line or as one big string?

– Jorge Campos
May 15 '16 at 15:59













Regex flavor is python 2.7, newlines should be included.

– Ram Rachum
May 15 '16 at 16:16





Regex flavor is python 2.7, newlines should be included.

– Ram Rachum
May 15 '16 at 16:16












4 Answers
4






active

oldest

votes


















29














You need a tempered greedy token:



abc(?:(?!abc|xyz|123).)*123(?:(?!abc|xyz).)*xyz


See the regex demo



To make sure it matches across lines, use re.DOTALL flag when compiling the regex.



Note that to achieve a better performance with such a heavy pattern, you should consider unrolling it. It can be done with negated character classes and negative lookaheads.



Pattern details:





  • abc - match abc


  • (?:(?!abc|xyz|123).)* - match any character that is not the starting point for a abc, xyz or 123 character sequences


  • 123 - a literal string 123


  • (?:(?!abc|xyz).)* - any character that is not the starting point for a abc or xyz character sequences


  • xyz - a trailing substring xyz


See the diagram below (if re.S is used, . will mean AnyChar):



enter image description here



See the Python demo:



import re

p = re.compile(r'abc(?:(?!abc|xyz|123).)*123(?:(?!abc|xyz).)*xyz', re.DOTALL)

s = "abc 123 xyznabc abc 123 xyznabc text 123 xyznabc text xyz xyz"

print(p.findall(s))

// => ['abc 123 xyz', 'abc 123 xyz', 'abc text 123 xyz']





share|improve this answer


























  • Can you please link the site from where you generated that state machine? I know a site exists with similar UI but can't find it though. Sorry for the irrelevant comment. I'll delete it soon :)

    – rafid059
    Mar 18 '17 at 18:24






  • 3





    See jex.im/regulex

    – Wiktor Stribiżew
    Mar 18 '17 at 20:10











  • Why the |123?

    – Stefan Pochmann
    Jan 24 '18 at 20:22











  • @StefanPochmann Well, you may get rid of that if you use a lazy quantifier in the first case: r'abc(?:(?!abc|xyz).)*?123(?:(?!abc|xyz).)*xyz'. It will work similarly.

    – Wiktor Stribiżew
    Jan 24 '18 at 20:26













  • Both are just optimizations, though, right? Not necessary?

    – Stefan Pochmann
    Jan 24 '18 at 20:26



















3














Using PCRE a solution would be:



This using m flag. If you want to check only from start and end of a line add ^ and $ at beginning and end respectively 



abc(?!.*(abc|xyz).*123).*123(?!.*(abc|xyz).*xyz).*xyz


Regular expression visualization



Debuggex Demo






share|improve this answer
























  • which software is used to draw diagram

    – Er. Amit Joshi
    Jun 3 '18 at 10:15











  • @Er.AmitJoshi It is not a software, it is the Debuggex Site there is a link in the answer

    – Jorge Campos
    Jun 4 '18 at 1:50



















2














The comment by hvd is quite appropriate, and this just provides an example. In SQL, for instance, I think it would be clearer to do:



where val like 'abc%123%xyz' and

      val not like 'abc%abc%' and

      val not like '%xyz%xyz'


I imagine something quite similar is simple to do in other environments.






share|improve this answer

































    1














    You could use lookaround.



    /^abc(?!.*abc).*123.*(?<!xyz.*)xyz$/g


    (I've not tested it.)






    share|improve this answer

























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      4 Answers
      4






      active

      oldest

      votes








      4 Answers
      4






      active

      oldest

      votes









      active

      oldest

      votes






      active

      oldest

      votes









      29














      You need a tempered greedy token:



      abc(?:(?!abc|xyz|123).)*123(?:(?!abc|xyz).)*xyz


      See the regex demo



      To make sure it matches across lines, use re.DOTALL flag when compiling the regex.



      Note that to achieve a better performance with such a heavy pattern, you should consider unrolling it. It can be done with negated character classes and negative lookaheads.



      Pattern details:





      • abc - match abc


      • (?:(?!abc|xyz|123).)* - match any character that is not the starting point for a abc, xyz or 123 character sequences


      • 123 - a literal string 123


      • (?:(?!abc|xyz).)* - any character that is not the starting point for a abc or xyz character sequences


      • xyz - a trailing substring xyz


      See the diagram below (if re.S is used, . will mean AnyChar):



      enter image description here



      See the Python demo:



      import re
      
p = re.compile(r'abc(?:(?!abc|xyz|123).)*123(?:(?!abc|xyz).)*xyz', re.DOTALL)
      
s = "abc 123 xyznabc abc 123 xyznabc text 123 xyznabc text xyz xyz"
      
print(p.findall(s))
      
// => ['abc 123 xyz', 'abc 123 xyz', 'abc text 123 xyz']





      share|improve this answer


























      • Can you please link the site from where you generated that state machine? I know a site exists with similar UI but can't find it though. Sorry for the irrelevant comment. I'll delete it soon :)

        – rafid059
        Mar 18 '17 at 18:24






      • 3





        See jex.im/regulex

        – Wiktor Stribiżew
        Mar 18 '17 at 20:10











      • Why the |123?

        – Stefan Pochmann
        Jan 24 '18 at 20:22











      • @StefanPochmann Well, you may get rid of that if you use a lazy quantifier in the first case: r'abc(?:(?!abc|xyz).)*?123(?:(?!abc|xyz).)*xyz'. It will work similarly.

        – Wiktor Stribiżew
        Jan 24 '18 at 20:26













      • Both are just optimizations, though, right? Not necessary?

        – Stefan Pochmann
        Jan 24 '18 at 20:26
















      29














      You need a tempered greedy token:



      abc(?:(?!abc|xyz|123).)*123(?:(?!abc|xyz).)*xyz


      See the regex demo



      To make sure it matches across lines, use re.DOTALL flag when compiling the regex.



      Note that to achieve a better performance with such a heavy pattern, you should consider unrolling it. It can be done with negated character classes and negative lookaheads.



      Pattern details:





      • abc - match abc


      • (?:(?!abc|xyz|123).)* - match any character that is not the starting point for a abc, xyz or 123 character sequences


      • 123 - a literal string 123


      • (?:(?!abc|xyz).)* - any character that is not the starting point for a abc or xyz character sequences


      • xyz - a trailing substring xyz


      See the diagram below (if re.S is used, . will mean AnyChar):



      enter image description here



      See the Python demo:



      import re
      
p = re.compile(r'abc(?:(?!abc|xyz|123).)*123(?:(?!abc|xyz).)*xyz', re.DOTALL)
      
s = "abc 123 xyznabc abc 123 xyznabc text 123 xyznabc text xyz xyz"
      
print(p.findall(s))
      
// => ['abc 123 xyz', 'abc 123 xyz', 'abc text 123 xyz']





      share|improve this answer


























      • Can you please link the site from where you generated that state machine? I know a site exists with similar UI but can't find it though. Sorry for the irrelevant comment. I'll delete it soon :)

        – rafid059
        Mar 18 '17 at 18:24






      • 3





        See jex.im/regulex

        – Wiktor Stribiżew
        Mar 18 '17 at 20:10











      • Why the |123?

        – Stefan Pochmann
        Jan 24 '18 at 20:22











      • @StefanPochmann Well, you may get rid of that if you use a lazy quantifier in the first case: r'abc(?:(?!abc|xyz).)*?123(?:(?!abc|xyz).)*xyz'. It will work similarly.

        – Wiktor Stribiżew
        Jan 24 '18 at 20:26













      • Both are just optimizations, though, right? Not necessary?

        – Stefan Pochmann
        Jan 24 '18 at 20:26














      29












      29








      29







      You need a tempered greedy token:



      abc(?:(?!abc|xyz|123).)*123(?:(?!abc|xyz).)*xyz


      See the regex demo



      To make sure it matches across lines, use re.DOTALL flag when compiling the regex.



      Note that to achieve a better performance with such a heavy pattern, you should consider unrolling it. It can be done with negated character classes and negative lookaheads.



      Pattern details:





      • abc - match abc


      • (?:(?!abc|xyz|123).)* - match any character that is not the starting point for a abc, xyz or 123 character sequences


      • 123 - a literal string 123


      • (?:(?!abc|xyz).)* - any character that is not the starting point for a abc or xyz character sequences


      • xyz - a trailing substring xyz


      See the diagram below (if re.S is used, . will mean AnyChar):



      enter image description here



      See the Python demo:



      import re
      
p = re.compile(r'abc(?:(?!abc|xyz|123).)*123(?:(?!abc|xyz).)*xyz', re.DOTALL)
      
s = "abc 123 xyznabc abc 123 xyznabc text 123 xyznabc text xyz xyz"
      
print(p.findall(s))
      
// => ['abc 123 xyz', 'abc 123 xyz', 'abc text 123 xyz']





      share|improve this answer















      You need a tempered greedy token:



      abc(?:(?!abc|xyz|123).)*123(?:(?!abc|xyz).)*xyz


      See the regex demo



      To make sure it matches across lines, use re.DOTALL flag when compiling the regex.



      Note that to achieve a better performance with such a heavy pattern, you should consider unrolling it. It can be done with negated character classes and negative lookaheads.



      Pattern details:





      • abc - match abc


      • (?:(?!abc|xyz|123).)* - match any character that is not the starting point for a abc, xyz or 123 character sequences


      • 123 - a literal string 123


      • (?:(?!abc|xyz).)* - any character that is not the starting point for a abc or xyz character sequences


      • xyz - a trailing substring xyz


      See the diagram below (if re.S is used, . will mean AnyChar):



      enter image description here



      See the Python demo:



      import re
      
p = re.compile(r'abc(?:(?!abc|xyz|123).)*123(?:(?!abc|xyz).)*xyz', re.DOTALL)
      
s = "abc 123 xyznabc abc 123 xyznabc text 123 xyznabc text xyz xyz"
      
print(p.findall(s))
      
// => ['abc 123 xyz', 'abc 123 xyz', 'abc text 123 xyz']






      share|improve this answer














      share|improve this answer



      share|improve this answer








      edited Dec 15 '17 at 9:14









      Eric Leschinski

      88.1k39323276




      88.1k39323276










      answered May 15 '16 at 16:20









      Wiktor StribiżewWiktor Stribiżew

      318k16139221




      318k16139221













      • Can you please link the site from where you generated that state machine? I know a site exists with similar UI but can't find it though. Sorry for the irrelevant comment. I'll delete it soon :)

        – rafid059
        Mar 18 '17 at 18:24






      • 3





        See jex.im/regulex

        – Wiktor Stribiżew
        Mar 18 '17 at 20:10











      • Why the |123?

        – Stefan Pochmann
        Jan 24 '18 at 20:22











      • @StefanPochmann Well, you may get rid of that if you use a lazy quantifier in the first case: r'abc(?:(?!abc|xyz).)*?123(?:(?!abc|xyz).)*xyz'. It will work similarly.

        – Wiktor Stribiżew
        Jan 24 '18 at 20:26













      • Both are just optimizations, though, right? Not necessary?

        – Stefan Pochmann
        Jan 24 '18 at 20:26



















      • Can you please link the site from where you generated that state machine? I know a site exists with similar UI but can't find it though. Sorry for the irrelevant comment. I'll delete it soon :)

        – rafid059
        Mar 18 '17 at 18:24






      • 3





        See jex.im/regulex

        – Wiktor Stribiżew
        Mar 18 '17 at 20:10











      • Why the |123?

        – Stefan Pochmann
        Jan 24 '18 at 20:22











      • @StefanPochmann Well, you may get rid of that if you use a lazy quantifier in the first case: r'abc(?:(?!abc|xyz).)*?123(?:(?!abc|xyz).)*xyz'. It will work similarly.

        – Wiktor Stribiżew
        Jan 24 '18 at 20:26













      • Both are just optimizations, though, right? Not necessary?

        – Stefan Pochmann
        Jan 24 '18 at 20:26

















      Can you please link the site from where you generated that state machine? I know a site exists with similar UI but can't find it though. Sorry for the irrelevant comment. I'll delete it soon :)

      – rafid059
      Mar 18 '17 at 18:24





      Can you please link the site from where you generated that state machine? I know a site exists with similar UI but can't find it though. Sorry for the irrelevant comment. I'll delete it soon :)

      – rafid059
      Mar 18 '17 at 18:24




      3




      3





      See jex.im/regulex

      – Wiktor Stribiżew
      Mar 18 '17 at 20:10





      See jex.im/regulex

      – Wiktor Stribiżew
      Mar 18 '17 at 20:10













      Why the |123?

      – Stefan Pochmann
      Jan 24 '18 at 20:22





      Why the |123?

      – Stefan Pochmann
      Jan 24 '18 at 20:22













      @StefanPochmann Well, you may get rid of that if you use a lazy quantifier in the first case: r'abc(?:(?!abc|xyz).)*?123(?:(?!abc|xyz).)*xyz'. It will work similarly.

      – Wiktor Stribiżew
      Jan 24 '18 at 20:26







      @StefanPochmann Well, you may get rid of that if you use a lazy quantifier in the first case: r'abc(?:(?!abc|xyz).)*?123(?:(?!abc|xyz).)*xyz'. It will work similarly.

      – Wiktor Stribiżew
      Jan 24 '18 at 20:26















      Both are just optimizations, though, right? Not necessary?

      – Stefan Pochmann
      Jan 24 '18 at 20:26





      Both are just optimizations, though, right? Not necessary?

      – Stefan Pochmann
      Jan 24 '18 at 20:26













      3














      Using PCRE a solution would be:



      This using m flag. If you want to check only from start and end of a line add ^ and $ at beginning and end respectively 



      abc(?!.*(abc|xyz).*123).*123(?!.*(abc|xyz).*xyz).*xyz


      Regular expression visualization



      Debuggex Demo






      share|improve this answer
























      • which software is used to draw diagram

        – Er. Amit Joshi
        Jun 3 '18 at 10:15











      • @Er.AmitJoshi It is not a software, it is the Debuggex Site there is a link in the answer

        – Jorge Campos
        Jun 4 '18 at 1:50
















      3














      Using PCRE a solution would be:



      This using m flag. If you want to check only from start and end of a line add ^ and $ at beginning and end respectively 



      abc(?!.*(abc|xyz).*123).*123(?!.*(abc|xyz).*xyz).*xyz


      Regular expression visualization



      Debuggex Demo






      share|improve this answer
























      • which software is used to draw diagram

        – Er. Amit Joshi
        Jun 3 '18 at 10:15











      • @Er.AmitJoshi It is not a software, it is the Debuggex Site there is a link in the answer

        – Jorge Campos
        Jun 4 '18 at 1:50














      3












      3








      3







      Using PCRE a solution would be:



      This using m flag. If you want to check only from start and end of a line add ^ and $ at beginning and end respectively 



      abc(?!.*(abc|xyz).*123).*123(?!.*(abc|xyz).*xyz).*xyz


      Regular expression visualization



      Debuggex Demo






      share|improve this answer













      Using PCRE a solution would be:



      This using m flag. If you want to check only from start and end of a line add ^ and $ at beginning and end respectively 



      abc(?!.*(abc|xyz).*123).*123(?!.*(abc|xyz).*xyz).*xyz


      Regular expression visualization



      Debuggex Demo







      share|improve this answer












      share|improve this answer



      share|improve this answer










      answered May 15 '16 at 16:15









      Jorge CamposJorge Campos

      17.1k63766




      17.1k63766













      • which software is used to draw diagram

        – Er. Amit Joshi
        Jun 3 '18 at 10:15











      • @Er.AmitJoshi It is not a software, it is the Debuggex Site there is a link in the answer

        – Jorge Campos
        Jun 4 '18 at 1:50



















      • which software is used to draw diagram

        – Er. Amit Joshi
        Jun 3 '18 at 10:15











      • @Er.AmitJoshi It is not a software, it is the Debuggex Site there is a link in the answer

        – Jorge Campos
        Jun 4 '18 at 1:50

















      which software is used to draw diagram

      – Er. Amit Joshi
      Jun 3 '18 at 10:15





      which software is used to draw diagram

      – Er. Amit Joshi
      Jun 3 '18 at 10:15













      @Er.AmitJoshi It is not a software, it is the Debuggex Site there is a link in the answer

      – Jorge Campos
      Jun 4 '18 at 1:50





      @Er.AmitJoshi It is not a software, it is the Debuggex Site there is a link in the answer

      – Jorge Campos
      Jun 4 '18 at 1:50











      2














      The comment by hvd is quite appropriate, and this just provides an example. In SQL, for instance, I think it would be clearer to do:



      where val like 'abc%123%xyz' and
      
      val not like 'abc%abc%' and
      
      val not like '%xyz%xyz'


      I imagine something quite similar is simple to do in other environments.






      share|improve this answer






























        2














        The comment by hvd is quite appropriate, and this just provides an example. In SQL, for instance, I think it would be clearer to do:



        where val like 'abc%123%xyz' and
        
      val not like 'abc%abc%' and
        
      val not like '%xyz%xyz'


        I imagine something quite similar is simple to do in other environments.






        share|improve this answer




























          2












          2








          2







          The comment by hvd is quite appropriate, and this just provides an example. In SQL, for instance, I think it would be clearer to do:



          where val like 'abc%123%xyz' and
          
      val not like 'abc%abc%' and
          
      val not like '%xyz%xyz'


          I imagine something quite similar is simple to do in other environments.






          share|improve this answer















          The comment by hvd is quite appropriate, and this just provides an example. In SQL, for instance, I think it would be clearer to do:



          where val like 'abc%123%xyz' and
          
      val not like 'abc%abc%' and
          
      val not like '%xyz%xyz'


          I imagine something quite similar is simple to do in other environments.







          share|improve this answer














          share|improve this answer



          share|improve this answer








          edited May 15 '16 at 16:11









          Jonathan Leffler

          568k916801031




          568k916801031










          answered May 15 '16 at 16:01









          Gordon LinoffGordon Linoff

          778k35307410




          778k35307410























              1














              You could use lookaround.



              /^abc(?!.*abc).*123.*(?<!xyz.*)xyz$/g


              (I've not tested it.)






              share|improve this answer






























                1














                You could use lookaround.



                /^abc(?!.*abc).*123.*(?<!xyz.*)xyz$/g


                (I've not tested it.)






                share|improve this answer




























                  1












                  1








                  1







                  You could use lookaround.



                  /^abc(?!.*abc).*123.*(?<!xyz.*)xyz$/g


                  (I've not tested it.)






                  share|improve this answer















                  You could use lookaround.



                  /^abc(?!.*abc).*123.*(?<!xyz.*)xyz$/g


                  (I've not tested it.)







                  share|improve this answer














                  share|improve this answer



                  share|improve this answer








                  edited May 15 '16 at 16:13

























                  answered May 15 '16 at 15:56









                  Kenny LauKenny Lau

                  321210




                  321210






























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