Recursive regex: unrecognized grouping structure

Question

I wrote a regex to parse a BibTex entry, but I think I used something that is not allowed in .net, as I get an Unrecognized grouping construct exception.

Can anyone spot my mistake?

 (?<entry>@(\w+)\{(\w+),(?<kvp>\W*([a-zA-Z]+) = \{(.+)\},)(?&kvp)*(\W*([a-zA-Z]+) = \{(.+)\})\W*\},?\s*)(?&entry)* 

Can be seen at https://regex101.com/r/uM0mV1/1

Answer 1

Here is how I would capture all the details in the line that you provided:

 @(?<type>\w+)\{(?<name>\w+),(?<kvps>\s*(?<attribute>\w+)\s*=\s*\{(?<value>.*?)},?\r?\n)+} 

Watch the demo

This regex works well because the C # regex engine saves all captured texts on the stack and can be accessed through Groups ["name"]. Captures .

C # code showing how to use it:

 var pattern = @"@(?<type>\w+)\{(?<name>\w+),(?<kvps>\s*(?<attribute>\w+)\s*=\s*\{(?<value>.*?)},?\r?\n)+}"; var matches = Regex.Matches(line, pattern); var cnt = 1; foreach (Match m in matches) { Console.WriteLine(string.Format("\nMatch {0}", cnt)); Console.WriteLine(m.Groups["type"].Value); Console.WriteLine(m.Groups["name"].Value); for (int i = 0; i < m.Groups["attribute"].Captures.Count; i++) { Console.WriteLine(string.Format("{0} - {1}", m.Groups["attribute"].Captures[i].Value, m.Groups["value"].Captures[i].Value)); } cnt++; } 

Output:

 Match 1 article Gettys90 author - Jim Gettys and Phil Karlton and Scott McGregor abstract - A technical overview of the X11 functionality. This is an update of the X10 TOG paper by Scheifler \& Gettys. journal - Software Practice and Experience volume - 20 number - S2 title - The {X} Window System, Version 11 year - 1990 Match 2 article Gettys90 author - Jim Gettys and Phil Karlton and Scott McGregor abstract - A technical overview of the X11 functionality. This is an update of the X10 TOG paper by Scheifler \& Gettys. journal - Software Practice and Experience volume - 20 number - S2 title - The {X} Window System, Version 11 year - 1990 Match 3 article Gettys90 author - Jim Gettys and Phil Karlton and Scott McGregor abstract - A technical overview of the X11 functionality. This is an update of the X10 TOG paper by Scheifler \& Gettys. journal - Software Practice and Experience volume - 20 number - S2 title - The {X} Window System, Version 11 year - 1990 

Answer 2

I assume that your incorrect address is not valid. See MSDN. Try to execute

 (?<entry>@(\w+)\{(\w+),(?<kvp>\W*([a-zA-Z]+) = \{(.+)\},)\k<kvp>*(\W*([a-zA-Z]+) = \{(.+)\})\W*\},?\s*)\k<entry>*