system.c

这是一个同样来自贝尔实验室的和UNIX有着渊源的操作系统, 其简洁的设计和实现易于我们学习和理解

#include "lib.h"
#include <stdlib.h>
#include <stdio.h>
#include <sys/wait.h>
#include <unistd.h>

int
system(const char *s)
{
	int w, status;
	pid_t pid;
	char cmd[30], *oty;

	oty = getenv("objtype");
	if(!oty)
		return -1;
	if(!s)
		return 1; /* a command interpreter is available */
	pid = fork();
	snprintf(cmd, sizeof cmd, "/%s/bin/ape/sh", oty);
	if(pid == 0) {
		execl(cmd, "sh", "-c", s, NULL);
		_exit(1);
	}
	if(pid < 0){
		_syserrno();
		return -1;
	}
	for(;;) {
		w = wait(&status);
		if(w == -1 || w == pid)
			break;
	}

	if(w == -1){
		_syserrno();
		return w;
	}
	return status;
}