#include<unistd.h>#include<stdio.h>#include<sys/types.h>#include<dirent.h>#define buflen 80int _cd(char *argv){//	if(argc==NULL)//	{//		getcwd(buffer,buflen);//		chdir(buffer);//	}        if(opendir(argv)==NULL)	{		printf("can't open %s",argv);		exit(0);	}	chdir(argv);	char buffer[buflen];	getcwd(buffer,buflen);	printf("cwd=%s\n", buffer);	exit(0);}