Awk - parentheses checking

If what you are trying to do is in a general purpose language, then this is not a trivial problem.

For starters, you have to worry about comments and lines. If you want to test this in a programming language that uses regular expressions, this again makes your quest more difficult.

So, before I can come and give you any advice on your question, I need to know the limits of your problem area. If you can guarantee that there are no strings, no comments, no regexes to worry about - or, more generally, nowhere in your code that can be used in parentheses other than the ones you check for balance , it will make life a lot easier.

It would be helpful to know the language you want to test.

If I take the hypothesis that there is no noise, i.e. all parentheses are useful parentheses, my strategy will be iterative:

I would just search and remove all the inner pairs of brackets: the ones that do not contain brackets inside. This is best done by collapsing all lines into one long line (and find a mechanism for adding line references if you need this information). In this case, find and replace is pretty simple:

This requires an array:

B["("]=")"; B["["]="]"; B["{"]="}"

      

        
        
        
      

    

And loop through these elements:

for (b in B) {gsub("[" b "][^][(){}]*[" B[b] "]", "", $0)}

      

        
        
        
      

    

My test file looks like this:

#!/bin/awk

($1 == "PID") {
  fo (i=1; i<NF; i++)
  {
    F[$i] = i
  }
}

($1 + 0) > 0 {
  count("VIRT")
  count("RES")
  count("SHR")
  count("%MEM")
}

END {
  pintf "VIRT=\t%12d\nRES=\t%12d\nSHR=\t%12d\n%%MEM=\t%5.1f%%\n", C["VIRT"], C["RES"], C["SHR"], C["%MEM"]
}

function count(c[)
{
  f=F[c];

  if ($f ~ /m$/)
  {
    $f = ($f+0) * 1024
  }

  C[c]+=($f+0)
}

      

        
        
        
      

    

My complete script (no line reference) looks like this:

cat test-file-for-brackets.txt | \
  tr -d '\r\n' | \
  awk \
  '
    BEGIN {
      B["("]=")";
      B["["]="]";
      B["{"]="}"
    }
    {
      m=1;
      while(m>0)
      {
        m=0;
        for (b in B)
        {
          m+=gsub("[" b "][^][(){}]*[" B[b] "]", "", $0)
        }
      };
      print
    }
  '

      

        
        
        
      

    

The output of this script stops at the innermost illegal use of parentheses. But be careful: 1 / this script won't work with parentheses in comments, regex or lines 2 / it doesn't tell you where the original file is, problem 3 / although it will remove all balanced pairs it stops on the innermost error conditions and holds all the capturing brackets.

Point 3 / is probably a useful result, although I'm not sure about the reporting mechanism you have in mind.

Point 2 / is relatively easy to implement, but it takes more than a few minutes of work, so I'll leave that to you to figure it out.

Point 1 / is tricky because you are introducing a whole new realm of competing sometimes nested beginnings and endings or special citation rules for special characters ...