PCRE regex to remove empty braces

Question

How can one write a regex to remove all pairs of braces that contain nothing?

For example, {} and {{}} should be reduced to an empty string, but {{} becomes { and {{A}{}} becomes {{A}}.

I'm currently running s/\{\}//g in a loop until the string length is fixed, but is there a better way to do this?

Answer 1

Matching balanced pairs using traditional regular expressions is difficult, if not impossible. Fortunately PCRE and others have an extension to match recursively, (?R) will recursively match the entire pattern.

/\{(?R)*\}/

That says to match brace pairs which have zero or more brace pairs inside them. See perlretut->Recursive patterns and perlre->Extended Patterns->?R for more information.

Answer 2

Without recursion:

1 while s/\{\}//g;