How do I write function using reg ex through preg_replace()

Question

assert(isCorrect('') === true);
assert(isCorrect('()') === true); 
assert(isCorrect('{()}') === true);
assert(isCorrect('{()}{}') === true); 
assert(isCorrect('(())') === true);
assert(isCorrect('{({({({()})})})}') === true); 
assert(isCorrect('{(})') === false);

this i have result for preg_match:

function isCorrect($source){
    return (bool)preg_match('~^((\(([^)(}{]|(?1))*\))|\{(?3)*\})*$~', $source);
}

Now I have the same thing only through preg_replace();

You are already using `preg_replace`. And what is logic behind this? — Justinas, Sep 24 '14 at 12:22
It is unclear what you are asking. Please adjust your question. — Jason McCreary, Sep 24 '14 at 12:26
@JasonMcCreary: it looks like OP is trying to check with a regex if a string consisting of parens is "correctly nested". That is, all parens are closed in same (actually: reverse) order as they were opened. — knittl, Sep 24 '14 at 12:29
@GordonFreeman you're not the only one who is confused, what exactly is your goal here? — andrew, Sep 24 '14 at 12:40
You're looking for [recursive patterns](http://php.net/manual/en/regexp.reference.recursive.php). — georg, Sep 24 '14 at 13:15

score 1 · Answer 1 · answered Sep 24 '14 at 15:38

Doing recursion could be a little tricky.
For sure you have to account for balanced pairs separately or it doesn't work.

If you expect just characters (){}, this one.

 # '~(\((?:(?>(?1))|)\)|\{(?:(?>(?1))|)\})~'

 (                      # (1 start)
      \(
      (?:
           (?> (?1) )
        |  
      )
      \)
   |  
      \{
      (?:
           (?> (?1) )
        |  
      )
      \}
 )                      # (1 end)

Or, if you expect other characters besides (){} inside, this one.

 #  '~(\((?:(?>[^(){}]+)|(?1))*\)|\{(?:(?>[^(){}]+)|(?1))*\})~'

 (                           # (1 start)
      \(
      (?:
           (?> [^(){}]+ )
        |  
           (?1) 
      )*
      \)
   |  
      \{
      (?:
           (?> [^(){}]+ )
        |  
           (?1) 
      )*
      \}
 )                           # (1 end)

score 0 · Accepted Answer · edited May 23 '17 at 12:05

^(($([^)(}{]|(?1))*$)|\{(?3)*\})*$ is the recursive pattern from my comment yesterday which checks if the string is composed of correctly nested ({}) / {()} from ^ start to $ end.

Assuming you want to replace all, that are correctly nested with empty string "" change it to:

$str = preg_replace('~\(([^)(}{]|(?0))*\)|\{(?1)*\}~', "", $str);

Test at regex101; Test at eval.in; Regex FAQ

Please rephrase your question, what acutally you're going to do, if that's not it.

How do I write function using reg ex through preg_replace()

2 Answers2