Perl Regex match balanced parentheses

Question

Following strings - match:

"MNO(A=(B=C) D=(E=F)) PQR(X=(G=H) I=(J=(K=L)))" - "MNO"
"MNO(A=(B=C) D=(E=F))" - "MNO"
"MNO" - "MNO"
"RAX.MNO(A=(B=C) D=(E=F)) PQR(X=(G=H) I=(J=(K=L)))" - "RAX.MNO"
"RAX.MNO(A=(B=C) D=(E=F))" - "RAX.MNO"
"RAX.MNO" - "RAX.MNO"

Inside every brace, there can be unlimited groups of them, but they have to be closed properly.

Any ideas? Don't know how to test properly for closure.

I have to use a Perl-Regular-Expression.

Are you sure you want to do this with regex? This will be recursive regex and, therefore, its not the best way to resolve the matter. Using classic solution via stack is much easier. — Alma Do, Sep 06 '13 at 08:43
This is possible in some regex flavors. Which one are you using? — Tim Pietzcker, Sep 06 '13 at 08:43
Also please clarify this in your question and I'll retract the duplicate flag. — Itay, Sep 06 '13 at 08:45
Why not match `PQR` in the first and fourth line? It's outside of any parentheses. — Tim Pietzcker, Sep 06 '13 at 08:50
Like previous commenters said, it depends on the flavour. .Net can do it using balancing groups, see http://blog.stevenlevithan.com/archives/balancing-groups for a really good overview. — Alex Paven, Sep 06 '13 at 08:52
http://stackoverflow.com/questions/4445674/can-i-use-perl-regular-expressions-to-match-balanced-text — georg, Sep 06 '13 at 08:57

Tim Pietzcker · Accepted Answer · 2013-09-06T09:55:42.083

4

In Perl or PHP, for example, you could use a regex like

/\((?:[^()]++|(?R))*\)/

to match balanced parentheses and their contents.

See it on regex101.

To remove all those matches from a string $subject in Perl, you could use

$subject =~ s/\((?:[^()]++|(?R))*\)//g;

Explanation:

\(       # Match a (
(?:      # Start of non-capturing group:
 [^()]++ # Either match one or more characters except (), don't backtrack 
|        # or
 (?R)    # Match the entire regex again, recursively
)*       # Any number of times
\)       # Match a )

edited Sep 06 '13 at 09:55

answered Sep 06 '13 at 08:49

Tim Pietzcker

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@RaphaelH: This regex works in Perl or PCRE (Perl-compatible regular expressions). – Tim Pietzcker Sep 06 '13 at 08:59
+1 Nice one. This is also mentioned in [perldoc perlre](http://perldoc.perl.org/perlre.html#%28?_PARNO_%29-%28?-_PARNO_%29-%28?+_PARNO_%29-%28?R%29-%28?0%29). It would be nice with a more detailed explanation. – TLP Sep 06 '13 at 09:11

Perl Regex match balanced parentheses

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