exec.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

		Xerror("can't open");
		return;
	}
	pushredir(ROPEN, f, runq->code[runq->pc].i);
	runq->pc++;
	poplist();
}

char*
list2str(word *words)
{
	char *value, *s, *t;
	int len = 0;
	word *ap;
	for(ap = words;ap;ap = ap->next)
		len+=1+strlen(ap->word);
	value = emalloc(len+1);
	s = value;
	for(ap = words;ap;ap = ap->next){
		for(t = ap->word;*t;) *s++=*t++;
		*s++=' ';
	}
	if(s==value)
		*s='\0';
	else s[-1]='\0';
	return value;
}

void
Xmatch(void)
{
	word *p;
	char *subject;
	subject = list2str(runq->argv->words);
	setstatus("no match");
	for(p = runq->argv->next->words;p;p = p->next)
		if(match(subject, p->word, '\0')){
			setstatus("");
			break;
		}
	efree(subject);
	poplist();
	poplist();
}

void
Xcase(void)
{
	word *p;
	char *s;
	int ok = 0;
	s = list2str(runq->argv->next->words);
	for(p = runq->argv->words;p;p = p->next){
		if(match(s, p->word, '\0')){
			ok = 1;
			break;
		}
	}
	efree(s);
	if(ok)
		runq->pc++;
	else
		runq->pc = runq->code[runq->pc].i;
	poplist();
}

word*
conclist(word *lp, word *rp, word *tail)
{
	char *buf;
	word *v;
	if(lp->next || rp->next)
		tail = conclist(lp->next==0?lp:lp->next, rp->next==0?rp:rp->next,
			tail);
	buf = emalloc(strlen(lp->word)+strlen(rp->word)+1);
	strcpy(buf, lp->word);
	strcat(buf, rp->word);
	v = newword(buf, tail);
	efree(buf);
	return v;
}

void
Xconc(void)
{
	word *lp = runq->argv->words;
	word *rp = runq->argv->next->words;
	word *vp = runq->argv->next->next->words;
	int lc = count(lp), rc = count(rp);
	if(lc!=0 || rc!=0){
		if(lc==0 || rc==0){
			Xerror1("null list in concatenation");
			return;
		}
		if(lc!=1 && rc!=1 && lc!=rc){
			Xerror1("mismatched list lengths in concatenation");
			return;
		}
		vp = conclist(lp, rp, vp);
	}
	poplist();
	poplist();
	runq->argv->words = vp;
}

void
Xassign(void)
{
	var *v;
	if(count(runq->argv->words)!=1){
		Xerror1("variable name not singleton!");
		return;
	}
	deglob(runq->argv->words->word);
	v = vlook(runq->argv->words->word);
	poplist();
	globlist();
	freewords(v->val);
	v->val = runq->argv->words;
	v->changed = 1;
	runq->argv->words = 0;
	poplist();
}
/*
 * copy arglist a, adding the copy to the front of tail
 */

word*
copywords(word *a, word *tail)
{
	word *v = 0, **end;
	for(end=&v;a;a = a->next,end=&(*end)->next)
		*end = newword(a->word, 0);
	*end = tail;
	return v;
}

void
Xdol(void)
{
	word *a, *star;
	char *s, *t;
	int n;
	if(count(runq->argv->words)!=1){
		Xerror1("variable name not singleton!");
		return;
	}
	s = runq->argv->words->word;
	deglob(s);
	n = 0;
	for(t = s;'0'<=*t && *t<='9';t++) n = n*10+*t-'0';
	a = runq->argv->next->words;
	if(n==0 || *t)
		a = copywords(vlook(s)->val, a);
	else{
		star = vlook("*")->val;
		if(star && 1<=n && n<=count(star)){
			while(--n) star = star->next;
			a = newword(star->word, a);
		}
	}
	poplist();
	runq->argv->words = a;
}

void
Xqdol(void)
{
	word *a, *p;
	char *s;
	int n;
	if(count(runq->argv->words)!=1){
		Xerror1("variable name not singleton!");
		return;
	}
	s = runq->argv->words->word;
	deglob(s);
	a = vlook(s)->val;
	poplist();
	n = count(a);
	if(n==0){
		pushword("");
		return;
	}
	for(p = a;p;p = p->next) n+=strlen(p->word);
	s = emalloc(n);
	if(a){
		strcpy(s, a->word);
		for(p = a->next;p;p = p->next){
			strcat(s, " ");
			strcat(s, p->word);
		}
	}
	else
		s[0]='\0';
	pushword(s);
	efree(s);
}

word*
subwords(word *val, int len, word *sub, word *a)
{
	int n;
	char *s;
	if(!sub)
		return a;
	a = subwords(val, len, sub->next, a);
	s = sub->word;
	deglob(s);
	n = 0;
	while('0'<=*s && *s<='9') n = n*10+ *s++ -'0';
	if(n<1 || len<n)
		return a;
	for(;n!=1;--n) val = val->next;
	return newword(val->word, a);
}

void
Xsub(void)
{
	word *a, *v;
	char *s;
	if(count(runq->argv->next->words)!=1){
		Xerror1("variable name not singleton!");
		return;
	}
	s = runq->argv->next->words->word;
	deglob(s);
	a = runq->argv->next->next->words;
	v = vlook(s)->val;
	a = subwords(v, count(v), runq->argv->words, a);
	poplist();
	poplist();
	runq->argv->words = a;
}

void
Xcount(void)
{
	word *a;
	char *s, *t;
	int n;
	char num[12];
	if(count(runq->argv->words)!=1){
		Xerror1("variable name not singleton!");
		return;
	}
	s = runq->argv->words->word;
	deglob(s);
	n = 0;
	for(t = s;'0'<=*t && *t<='9';t++) n = n*10+*t-'0';
	if(n==0 || *t){
		a = vlook(s)->val;
		inttoascii(num, count(a));
	}
	else{
		a = vlook("*")->val;
		inttoascii(num, a && 1<=n && n<=count(a)?1:0);
	}
	poplist();
	pushword(num);
}

void
Xlocal(void)
{
	if(count(runq->argv->words)!=1){
		Xerror1("variable name must be singleton\n");
		return;
	}
	deglob(runq->argv->words->word);
	runq->local = newvar(strdup(runq->argv->words->word), runq->local);
	runq->local->val = copywords(runq->argv->next->words, (word *)0);
	runq->local->changed = 1;
	poplist();
	poplist();
}

void
Xunlocal(void)
{
	var *v = runq->local, *hid;
	if(v==0)
		panic("Xunlocal: no locals!", 0);
	runq->local = v->next;
	hid = vlook(v->name);
	hid->changed = 1;
	efree(v->name);
	freewords(v->val);
	efree((char *)v);
}

void
freewords(word *w)
{
	word *nw;
	while(w){
		efree(w->word);
		nw = w->next;
		efree((char *)w);
		w = nw;
	}
}

void
Xfn(void)
{
	var *v;
	word *a;
	int end;
	end = runq->code[runq->pc].i;
	for(a = runq->argv->words;a;a = a->next){
		v = gvlook(a->word);
		if(v->fn)
			codefree(v->fn);
		v->fn = codecopy(runq->code);
		v->pc = runq->pc+2;
		v->fnchanged = 1;
	}
	runq->pc = end;
	poplist();
}

void
Xdelfn(void)
{
	var *v;
	word *a;
	for(a = runq->argv->words;a;a = a->next){
		v = gvlook(a->word);
		if(v->fn)
			codefree(v->fn);
		v->fn = 0;
		v->fnchanged = 1;
	}
	poplist();
}

char*
concstatus(char *s, char *t)
{
	static char v[NSTATUS+1];
	int n = strlen(s);
	strncpy(v, s, NSTATUS);
	if(n<NSTATUS){
		v[n]='|';
		strncpy(v+n+1, t, NSTATUS-n-1);
	}
	v[NSTATUS]='\0';
	return v;
}

void
Xpipewait(void)
{
	char status[NSTATUS+1];
	if(runq->pid==-1)
		setstatus(concstatus(runq->status, getstatus()));
	else{
		strncpy(status, getstatus(), NSTATUS);
		status[NSTATUS]='\0';
		Waitfor(runq->pid, 1);
		runq->pid=-1;
		setstatus(concstatus(getstatus(), status));
	}
}

void
Xrdcmds(void)
{
	struct thread *p = runq;
	word *prompt;
	flush(err);
	nerror = 0;
	if(flag['s'] && !truestatus())
		pfmt(err, "status=%v\n", vlook("status")->val);
	if(runq->iflag){
		prompt = vlook("prompt")->val;
		if(prompt)
			promptstr = prompt->word;
		else
			promptstr="% ";
	}
	Noerror();
	if(yyparse()){
		if(!p->iflag || p->eof && !Eintr()){
			if(p->cmdfile)
				efree(p->cmdfile);
			closeio(p->cmdfd);
			Xreturn();	/* should this be omitted? */
		}
		else{
			if(Eintr()){
				pchr(err, '\n');
				p->eof = 0;
			}
			--p->pc;	/* go back for next command */
		}
	}
	else{
		ntrap = 0;	/* avoid double-interrupts during blocked writes */
		--p->pc;	/* re-execute Xrdcmds after codebuf runs */
		start(codebuf, 1, runq->local);
	}
	freenodes();
}

void
Xerror(char *s)
{
	if(strcmp(argv0, "rc")==0 || strcmp(argv0, "/bin/rc")==0)
		pfmt(err, "rc: %s: %r\n", s);
	else
		pfmt(err, "rc (%s): %s: %r\n", argv0, s);
	flush(err);
	while(!runq->iflag) Xreturn();
}

void
Xerror1(char *s)
{
	if(strcmp(argv0, "rc")==0 || strcmp(argv0, "/bin/rc")==0)
		pfmt(err, "rc: %s\n", s);
	else
		pfmt(err, "rc (%s): %s\n", argv0, s);
	flush(err);
	while(!runq->iflag) Xreturn();
}

void
setstatus(char *s)
{
	setvar("status", newword(s, (word *)0));
}

char*
getstatus(void)
{
	var *status = vlook("status");
	return status->val?status->val->word:"";
}

int
truestatus(void)
{
	char *s;
	for(s = getstatus();*s;s++)
		if(*s!='|' && *s!='0')
			return 0;
	return 1;
}

void
Xdelhere(void)
{
	Unlink(runq->code[runq->pc++].s);
}

void
Xfor(void)
{
	if(runq->argv->words==0){
		poplist();
		runq->pc = runq->code[runq->pc].i;
	}
	else{
		freelist(runq->local->val);
		runq->local->val = runq->argv->words;
		runq->local->changed = 1;
		runq->argv->words = runq->argv->words->next;
		runq->local->val->next = 0;
		runq->pc++;
	}
}

void
Xglob(void)
{
	globlist();
}