Remove outermost parentheses

I am having problem while removing outermost parentheses from a string using GREL. What i am trying to do is simply remove outermost parentheses and all other parentheses should be kept intact. Below is what i am trying to do using regex -

value.split(/(abc+/)

and below is my sample string that i am trying to parse and desired output.

Foo ( test1 test2 ) => Foo test1 test2
Bar ( test1 t3() test2 ) => Bar test1 t3() test2
Baz ((("Fdsfds"))) => Baz (("Fdsfds"))

I would appreciate any help.

One option could be to use a capturing group and in the replacement use the first capturing group.

Note that this does not take balanced parenthesis into account.

It matches the outer parenthesis, then captures in a group what is inside and matches an outer parenthesis again.

Inside the capturing group is an alternation that matches not () or from an openening till closing parenthesis.

\((\(*(?:[^)(]*|\([^)]*\))*\)*)\)

Explanation

• \( Match outer parenthesis (
• ( Capture group -\(* Match 0+ times (
  • (?: Non capturing group
    • [^)(]* Match 0+ times not ( or )
    • | Or
    • \([^)]*\) Match from ( till next ) closing parenthesis
  • )* Close non capturing group and repeat 0+ times
  • \)* Match 0+ times a closing parenthesis
• ) Close capture group
• \) Match outer closing parenthesis

Regex demo