implement Chgrp; include "sys.m";	sys: Sys; include "draw.m"; include "arg.m"; Chgrp: module{	init:	fn(nil: ref Draw->Context, nil: list of string);}; usage(){	sys->fprint(sys->fildes(2), "usage: chgrp [-uo] group file ...\n");	raise "fail:usage";} init(nil: ref Draw->Context, args: list of string){	sys = load Sys Sys->PATH; 	arg := load Arg Arg->PATH;	if(arg == nil){		sys->fprint(sys->fildes(2), "chgrp: can't load %s: %r\n", Arg->PATH);		raise "fail:load";	}	setuser := 0;	arg->init(args);	while((o := arg->opt()) != 0)		case o {		'o' or 'u' =>			setuser = 1;		* =>			usage();		}	args = arg->argv();	arg = nil;	if(args == nil)		usage();	id := hd args;	err := 0;	while((args = tl args) != nil){		d := sys->nulldir;		if(setuser)			d.uid = id;		else			d.gid = id;		if(sys->wstat(hd args, d) < 0){			sys->fprint(sys->fildes(2), "chgrp: can't change %s: %r\n", hd args);			err = 1;		}	}	if(err)		raise "fail:error";}