exec.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

void redirect_to(char *filename)
{
	int fd = open(filename, O_RDWR | O_CREAT, 0666);

	if(fd == -1){
		perror("open");
		return;
	}
	dup2(fd,STDOUT_FILENO);
	dup2(fd,STDERR_FILENO);
	close(fd);
}

int main(int argc, const char *argv[])
{
	pid_t pid = fork();

	if(pid < 0){
		fprintf(stderr, "Fork failed.\n");
	}else if(pid > 0){
		redirect_to("log");
		execl("/bin/ls", "ls", "-l", (char*)0);
	}else{
		redirect_to("log2");
		printf("abc\n");
		fprintf(stderr, "123\n");
	}
	return 0;
}