how to validate regular expression for balance brackets in ruby?

Question

please help me to validate balance brackets for string. my test string is below.

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score 3 · Answer 1 · answered Jan 12 '15 at 13:15

The following regex is taken from Programming Ruby:

re = /
  \A
    (?<brace_expression>
      {
        (
          [^{}] # anything other than braces
        | # ...or...
          \g<brace_expression> # a nested brace expression
        )*
      }
    )
  \Z
/x

\g<brace_expression> here is used recursively.

score 2 · Answer 2 · edited May 23 '17 at 10:28

2

Unfortunately, this isn't possible to determine using regular expressions. This is because regular expressions recognize regular languages, and nested patterns (which is essentially what you're asking for here) aren't part of regular languages.

"Can regular expressions be used to match nested patterns?" goes in to a little more detail on the subject.

Edit: Turns out Ruby's regex engine does support this. See Yu Hao's answer.

edited May 23 '17 at 10:28

Community

1
1

answered Jan 12 '15 at 13:12

joost

129
2
9

That's true for common regex, but don't forget Ruby's regex engine supports many extensions. – Yu Hao Jan 12 '15 at 13:26
1

Good one, I hadn't taken that into account (actually learned this from your post :) ) – joost Jan 12 '15 at 15:39

how to validate regular expression for balance brackets in ruby?

2 Answers2