#include <errno.h>
#include <signal.h>
#include <sys/wait.h>
#include <unistd.h>

int system(const char *cmdstring) {
  pid_t pid;
  int status;
  struct sigaction ignore, saveintr, savequit;
  sigset_t chldmask, savemask;

  if (cmdstring == NULL)
    return 1;

  ignore.sa_handler = SIG_IGN;
  sigemptyset(&ignore.sa_mask);
  ignore.sa_flags = 0;
  if (sigaction(SIGINT, &ignore, &saveintr) < 0)
    return -1;
  if (sigaction(SIGQUIT, &ignore, &savequit) < 0)
    return -1;
  sigemptyset(&chldmask);
  sigaddset(&chldmask, SIGCHLD);
  if (sigprocmask(SIG_BLOCK, &chldmask, &savemask) < 0)
    return -1;

  if((pid = fork()) < 0) {
    status = -1;
  }
  else if (pid == 0) {
    sigaction(SIGINT, &saveintr, NULL);
    sigaction(SIGQUIT, &savequit, NULL);
    execl("/bin/sh", "sh", "-c", cmdstring, (char *)0);
    _exit(127);
  }
  else {
    while (waitpid(pid, &status, 0) < 0)
      if (errno != EINTR) {
        return -1;
        break;
      }
  }

  if(sigaction(SIGINT, &saveintr, NULL) < 0) {
    return -1;
  }
  if(sigaction(SIGQUIT, &savequit, NULL) < 0) {
    return -1;
  }
  if(sigprocmask(SIG_SETMASK, &savemask, NULL) < 0) {
    return -1;
  }

  return status;
}

int main(void) {
  return system("ls .");
}