Recursive regex for matching everything in parenthesis (PCRE)

Question

I am surprised to not easily find a similar question with an answer on SO. I would like to match everything in some functions. The idea is to remove the functions which are useless.

foo(some (content)) --> some (content)

So I am trying to match everything in the function call which can include parenthesis. Here is my PCRE regex:

(?<name>\w+)\s*\(\K
(?<e>
     [^()]+
     |
     [^()]*
         \((?&e)\)
     [^()]*
)*
(?=\))

https://regex101.com/r/gfMAIM/1

Unfortunately it doesn't work and I don't really understand why.

Answer 1

Your Group e pattern does not do the right job, currently, it matches parentheses with 1 depth level as you only recursed the e pattern once. It needs to match as many (...) substrings as there are present, and thus, the subroutine pattern needs to be inside a * or + quantified group, and it can even be "simplified" to (?<e>[^()]*(?:\((?&e)\)[^()]*)*).

Note that your Group e pattern is equal to (?<e>[^()]+|\((?&e)\))*. [^()]* around \((?&e)\) are redundant since the [^()]+ alternative will consume the chars other than ( and ) on the current depth level.

Also, you quantified the Group e pattern making it a repeated capturing group that only keeps the text matched during the last iteration.

You may use

(?<name>\w+)\s*\(\K(?<e>[^()]*(?:\((?&e)\)[^()]*)*)(?=\))

See the regex demo

Details

• (?<name>\w+)\s*\(\K - 1+ word chars, 0+ whitespaces and ( that are omitted from the match
• (?<e> - start of Group e
  • [^()]* - 0+ chars other than ( and )
  • (?: - start of a non-capturing group:
    • \( - a ( char
    • (?&e) - Group e pattern recursed
    • \) - a )
    • [^()]* - 0+ chars other than ( and )
  • )* - 0 or more repetitions
• ) - end of e group
• (?=\)) - a ) must be immediately to the right of the current location.

Answer 2

The following regex does the matching without taking extra steps:

(?<name>\w+)\s*(\((?<e>([^()]*+|(?2))+)\))

See live demo here

But that doesn't match following strings that contain unbalanced parentheses in a quoted string:

• foo(bar = ')')
• foo(bar(john = "(Doe..."))

So what you should look for is:

(?<name>\w+)\s*(\((?<e>([^()'"]*+|"(?>[^"\\]*+|\\.)*"|'(?>[^'\\]*+|\\.)*'|(?2))+)\))

See live demo here

Regex breakdown:

• (?<name>\w+)\s* Match function name and trailing spaces
• ( Start of a cluster
  • \( Match a literal (
  • (?<e> Start of named capturing group e
    • ( Start of capturing group #2
      • [^()'"]*+ Match any thing except ()'"
      • | Or
      • "(?>[^"\\]*+|\\.)*" Match any thing between double quotes
      • | Or
      • '(?>[^'\\]*+|\\.)*' Match any thing between single quotes
      • | Or
      • (?2) Recurse second capturing group
    • )+ Repeat as much as possible, at least once
  • ) End of capturing group
  • \) Match ) literally
• ) End of capturing group