Although I tried different existing editors like sed or replace, non of it got it right for me. All implementations waited for a newline to work with the data. I also tried disabling every possible buffer but the problem still persists.

So after quite some trial and error I started writing my own little program which could do the job. So here is the code:

#include <stdio.h>
#include <string.h>

int main (int argc, char* argv[])
{
  setbuf(stdin,NULL);
  char c;
  int tag =0;
  do {
    c = getchar();
    if (c == '<' && tag==0) ++tag;
    if (c == '>' && tag>0) {--tag; c='\n';}
    if (tag ==0 ){
      putchar(c);
      fflush(stdout);
    }
  } while (c != EOF);
  return 0;
}

Just compile it with the following statement and it will filter everything which comes from stdin.

gcc -fPIC -Wall -otransform transform.c

Here is a sample statement of how to use it:

curl -N -s google.com | ./transform