#include <unistd.h>
int main()
{
  int ret;
  ret = execl ("/bin/ls", "ls", "-1", (char *)0);
  return 0;
}

#include <stdio.h>
#include <unistd.h>
int main()
{
  FILE *fp;
  int ret;
  int id,fd;
  fp=fopen("/home/user/00.txt","w");
  id = dup(STDOUT_FILENO);
  fd=fileno(fp);
  dup2(fd, STDOUT_FILENO);
  ret = execl ("/bin/ls", "ls", "-1", (char *)0);
  dup2(id, STDOUT_FILENO);
  fclose(fp);
  return 0;
}