#include <u.h>#include <libc.h> int	readgid(char*);int	uflag; voidmain(int argc, char *argv[]){	int i;	Dir dir;	char *group;	char *errs; 	ARGBEGIN {	default:	usage:		fprint(2, "usage: chgrp [ -uo ] group file ....\n");		exits("usage");		return;	case 'u':	case 'o':		uflag++;		break;	} ARGEND	if(argc < 1)		goto usage; 	group = argv[0];	errs = 0;	for(i=1; i<argc; i++){		nulldir(&dir);		if(uflag)			dir.uid = group;		else			dir.gid = group;		if(dirwstat(argv[i], &dir) == -1) {			fprint(2, "chgrp: can't wstat %s: %r\n", argv[i]);			errs = "can't wstat";			continue;		}	}	exits(errs);}