/* log file cmd args... */
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

int main(int argc, char* argv[])
{ 
  int p[2];
  pipe(p);
  char c;

  if(fork()) { /* père */
    int fd = open(argv[1], O_WRONLY | O_CREAT | O_TRUNC, 0644);
    if(fd < 0) exit(EXIT_FAILURE);
    close(p[1]); /* ici, sinon read() bloquera à la fin ! */
    while(read(p[0], &c, 1) > 0) {
      write(1, &c, 1);
      write(fd, &c, 1);
    }
    close(fd); 
    close(p[0]);
  }
  else { /* fils */
    close(p[0]);
    dup2(p[1], 1);
    close(p[1]);
    execvp(argv[2], argv+2);
    exit(EXIT_FAILURE);
  }
  
  return EXIT_SUCCESS;
}