linux sleep with exec /bin/sleep

sleep .5 # Waits 0.5 second.
sleep 5  # Waits 5 seconds.
sleep 5s # Waits 5 seconds.
sleep 5m # Waits 5 minutes.
sleep 5h # Waits 5 hours.
sleep 5d # Waits 5 days.

int pid= fork();
if (pid==0) { // child
	execl("/bin/sleep", "sleep", argv[1], NULL); // argv[1] is the sleeptime
    perror("execl");
    return EXIT_FAILURE;
}
if (waitpid(pid,NULL,0)<0) {
	perror("waitpid");
    return EXIT_FAILURE;
}