Linux : system()

system.c

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

int system(const char *cmd){
	pid_t pid;
	int status;
	
	if((pid=fork())<0){
		status=-1;
	}else if(pid==0){
		execl("/bin/sh","sh","-c",cmd,(char*)0);
		_exit(127);
	}else{
		while(waitpid(pid,&status,0)<0)
		if(errno != EINTR){
			status=-1;
			break;
		}
	}
	return status;
}

int main(int argc, char **argv, char **envp){
	while(*envp)
		printf("%s\n",*envp++);

	system("who");
	system("nocommand");
	system("cal");

	return 0;
}