implement Shellbuiltin; include "sys.m";	sys: Sys;include "draw.m";include "sh.m";	sh: Sh;	Listnode, Context: import sh;	myself: Shellbuiltin; initbuiltin(ctxt: ref Context, shmod: Sh): string{	sys = load Sys Sys->PATH;	sh = shmod;	myself = load Shellbuiltin "$self";	if (myself == nil)		ctxt.fail("bad module", sys->sprint("echo: cannot load self: %r"));	ctxt.addbuiltin("echo", myself);	return nil;} whatis(nil: ref Sh->Context, nil: Sh, nil: string, nil: int): string{	return nil;} getself(): Shellbuiltin{	return myself;} runbuiltin(ctxt: ref Context, nil: Sh,			argv: list of ref Listnode, last: int): string{	case (hd argv).word {	"echo" =>		return builtin_echo(ctxt, argv, last);	}	return nil;} runsbuiltin(nil: ref Sh->Context, nil: Sh,			nil: list of ref Listnode): list of ref Listnode{	return nil;} argusage(ctxt: ref Context){	ctxt.fail("usage", "usage: arg [opts {command}]... - args");} # converted from /appl/cmd/echo.b.# should have exactly the same semantics.builtin_echo(nil: ref Context, argv: list of ref Listnode, nil: int): string{	argv = tl argv;	nonewline := 0;	if (len argv > 0) {		w := (hd argv).word;		if (w == "-n" || w == "--") {			nonewline = (w == "-n");			argv = tl argv;		}	}	s := "";	if (argv != nil) {		s = word(hd argv);		for (argv = tl argv; argv != nil; argv = tl argv)			s += " " + word(hd argv);	}	if (nonewline == 0) 		s[len s] = '\n';	{		a := array of byte s;		if (sys->write(sys->fildes(1), a, len a) != len a) {			sys->fprint(sys->fildes(2), "echo: write error: %r\n");			return "write error";		}		return nil;	}	exception{		"write on closed pipe" =>			sys->fprint(sys->fildes(2), "echo: write error: write on closed pipe\n");			return "write error";	}} word(n: ref Listnode): string{	if (n.word != nil)		return n.word;	if (n.cmd != nil)		n.word = sh->cmd2string(n.cmd);	return n.word;}