eval.c

操作系统源代码

		if (lp->next) {
			if (pipe(pip) < 0) {
				close(prevfd);
				error("Pipe call failed");
			}
		}
		if (forkshell(jp, lp->n, n->npipe.backgnd) == 0) {
			INTON;
			if (prevfd > 0) {
				close(0);
				copyfd(prevfd, 0);
				close(prevfd);
			}
			if (pip[1] >= 0) {
				close(pip[0]);
				if (pip[1] != 1) {
					close(1);
					copyfd(pip[1], 1);
					close(pip[1]);
				}
			}
			evaltree(lp->n, EV_EXIT);
		}
		if (prevfd >= 0)
			close(prevfd);
		prevfd = pip[0];
		close(pip[1]);
	}
	INTON;
	if (n->npipe.backgnd == 0) {
		INTOFF;
		exitstatus = waitforjob(jp);
		TRACE(("evalpipe:  job done exit status %d\n", exitstatus));
		INTON;
	}
}



/*
 * Execute a command inside back quotes.  If it's a builtin command, we
 * want to save its output in a block obtained from malloc.  Otherwise
 * we fork off a subprocess and get the output of the command via a pipe.
 * Should be called with interrupts off.
 */

void
evalbackcmd(n, result)
	union node *n;
	struct backcmd *result;
	{
	int pip[2];
	struct job *jp;
	struct stackmark smark;		/* unnecessary */

	setstackmark(&smark);
	result->fd = -1;
	result->buf = NULL;
	result->nleft = 0;
	result->jp = NULL;
	if (n == NULL) {
		/* `` */
	} else
	if (n->type == NCMD) {
		evalcommand(n, EV_BACKCMD, result);
	} else {
		if (pipe(pip) < 0)
			error("Pipe call failed");
		jp = makejob(n, 1);
		if (forkshell(jp, n, FORK_NOJOB) == 0) {
			FORCEINTON;
			close(pip[0]);
			if (pip[1] != 1) {
				close(1);
				copyfd(pip[1], 1);
				close(pip[1]);
			}
			evaltree(n, EV_EXIT);
		}
		close(pip[1]);
		result->fd = pip[0];
		result->jp = jp;
	}
	popstackmark(&smark);
	TRACE(("evalbackcmd done: fd=%d buf=0x%x nleft=%d jp=0x%x\n",
		result->fd, result->buf, result->nleft, result->jp));
}



/*
 * Execute a simple command.
 */

STATIC void
evalcommand(cmd, flags, backcmd)
	union node *cmd;
	struct backcmd *backcmd;
	{
	struct stackmark smark;
	union node *argp;
	struct arglist arglist;
	struct arglist varlist;
	char **argv;
	int argc;
	char **envp;
	int varflag;
	struct strlist *sp;
	register char *p;
	int mode;
	int pip[2];
	struct cmdentry cmdentry;
	struct job *jp;
	struct jmploc jmploc;
	struct jmploc *volatile savehandler;
	char *volatile savecmdname;
	volatile struct shparam saveparam;
	struct localvar *volatile savelocalvars;
	volatile int e;
	char *lastarg;

	/* First expand the arguments. */
	TRACE(("evalcommand(0x%x, %d) called\n", (int)cmd, flags));
	setstackmark(&smark);
	arglist.lastp = &arglist.list;
	varlist.lastp = &varlist.list;
	varflag = 1;
	for (argp = cmd->ncmd.args ; argp ; argp = argp->narg.next) {
		p = argp->narg.text;
		if (varflag && is_name(*p)) {
			do {
				p++;
			} while (is_in_name(*p));
			if (*p == '=') {
				expandarg(argp, &varlist, 0);
				continue;
			}
		}
		expandarg(argp, &arglist, 1);
		varflag = 0;
	}
	*arglist.lastp = NULL;
	*varlist.lastp = NULL;
	expredir(cmd->ncmd.redirect);
	argc = 0;
	for (sp = arglist.list ; sp ; sp = sp->next)
		argc++;
	argv = stalloc(sizeof (char *) * (argc + 1));
	for (sp = arglist.list ; sp ; sp = sp->next)
		*argv++ = sp->text;
	*argv = NULL;
	lastarg = NULL;
	if (iflag && funcnest == 0 && argc > 0)
		lastarg = argv[-1];
	argv -= argc;

	/* Print the command if xflag is set. */
	if (xflag) {
		outc('+', &errout);
		for (sp = varlist.list ; sp ; sp = sp->next) {
			outc(' ', &errout);
			out2str(sp->text);
		}
		for (sp = arglist.list ; sp ; sp = sp->next) {
			outc(' ', &errout);
			out2str(sp->text);
		}
		outc('\n', &errout);
		flushout(&errout);
	}

	/* Now locate the command. */
	if (argc == 0) {
		cmdentry.cmdtype = CMDBUILTIN;
		cmdentry.u.index = BLTINCMD;
	} else {
		find_command(argv[0], &cmdentry, 1);
		if (cmdentry.cmdtype == CMDUNKNOWN) {	/* command not found */
			exitstatus = 2;
			flushout(&errout);
			return;
		}
		/* implement the bltin builtin here */
		if (cmdentry.cmdtype == CMDBUILTIN && cmdentry.u.index == BLTINCMD) {
			for (;;) {
				argv++;
				if (--argc == 0)
					break;
				if ((cmdentry.u.index = find_builtin(*argv)) < 0) {
					outfmt(&errout, "%s: not found\n", *argv);
					exitstatus = 2;
					flushout(&errout);
					return;
				}
				if (cmdentry.u.index != BLTINCMD)
					break;
			}
		}
	}

	/* Fork off a child process if necessary. */
	if (cmd->ncmd.backgnd
	 || cmdentry.cmdtype == CMDNORMAL && (flags & EV_EXIT) == 0
	 || (flags & EV_BACKCMD) != 0
	    && (cmdentry.cmdtype != CMDBUILTIN
		 || cmdentry.u.index == DOTCMD
		 || cmdentry.u.index == EVALCMD)) {
		jp = makejob(cmd, 1);
		mode = cmd->ncmd.backgnd;
		if (flags & EV_BACKCMD) {
			mode = FORK_NOJOB;
			if (pipe(pip) < 0)
				error("Pipe call failed");
		}
		if (forkshell(jp, cmd, mode) != 0)
			goto parent;	/* at end of routine */
		if (flags & EV_BACKCMD) {
			FORCEINTON;
			close(pip[0]);
			if (pip[1] != 1) {
				close(1);
				copyfd(pip[1], 1);
				close(pip[1]);
			}
		}
		flags |= EV_EXIT;
	}

	/* This is the child process if a fork occurred. */
	/* Execute the command. */
	if (cmdentry.cmdtype == CMDFUNCTION) {
		trputs("Shell function:  ");  trargs(argv);
		redirect(cmd->ncmd.redirect, REDIR_PUSH);
		saveparam = shellparam;
		shellparam.malloc = 0;
		shellparam.nparam = argc - 1;
		shellparam.p = argv + 1;
		shellparam.optnext = NULL;
		INTOFF;
		savelocalvars = localvars;
		localvars = NULL;
		INTON;
		if (setjmp(jmploc.loc)) {
			if (exception == EXSHELLPROC)
				freeparam((struct shparam *)&saveparam);
			else {
				freeparam(&shellparam);
				shellparam = saveparam;
			}
			poplocalvars();
			localvars = savelocalvars;
			handler = savehandler;
			longjmp(handler->loc, 1);
		}
		savehandler = handler;
		handler = &jmploc;
		for (sp = varlist.list ; sp ; sp = sp->next)
			mklocal(sp->text);
		funcnest++;
		evaltree(cmdentry.u.func, 0);
		funcnest--;
		INTOFF;
		poplocalvars();
		localvars = savelocalvars;
		freeparam(&shellparam);
		shellparam = saveparam;
		handler = savehandler;
		popredir();
		INTON;
		if (evalskip == SKIPFUNC) {
			evalskip = 0;
			skipcount = 0;
		}
		if (flags & EV_EXIT)
			exitshell(exitstatus);
	} else if (cmdentry.cmdtype == CMDBUILTIN) {
		trputs("builtin command:  ");  trargs(argv);
		mode = (cmdentry.u.index == EXECCMD)? 0 : REDIR_PUSH;
		if (flags == EV_BACKCMD) {
			memout.nleft = 0;
			memout.nextc = memout.buf;
			memout.bufsize = 64;
			mode |= REDIR_BACKQ;
		}
		redirect(cmd->ncmd.redirect, mode);
		savecmdname = commandname;
		cmdenviron = varlist.list;
		e = -1;
		if (setjmp(jmploc.loc)) {
			e = exception;
			exitstatus = (e == EXINT)? SIGINT+128 : 2;
			goto cmddone;
		}
		savehandler = handler;
		handler = &jmploc;
		commandname = argv[0];
		argptr = argv + 1;
		optptr = NULL;			/* initialize nextopt */
		exitstatus = (*builtinfunc[cmdentry.u.index])(argc, argv);
		flushall();
cmddone:
		out1 = &output;
		out2 = &errout;
		freestdout();
		if (e != EXSHELLPROC) {
			commandname = savecmdname;
			if (flags & EV_EXIT) {
				exitshell(exitstatus);
			}
		}
		handler = savehandler;
		if (e != -1) {
			if (e != EXERROR || cmdentry.u.index == BLTINCMD
					       || cmdentry.u.index == DOTCMD
					       || cmdentry.u.index == EVALCMD
					       || cmdentry.u.index == EXECCMD)
				exraise(e);
			FORCEINTON;
		}
		if (cmdentry.u.index != EXECCMD)
			popredir();
		if (flags == EV_BACKCMD) {
			backcmd->buf = memout.buf;
			backcmd->nleft = memout.nextc - memout.buf;
			memout.buf = NULL;
		}
	} else {
		trputs("normal command:  ");  trargs(argv);
		clearredir();
		redirect(cmd->ncmd.redirect, 0);
		if (varlist.list) {
			p = stalloc(strlen(pathval()) + 1);
			scopy(pathval(), p);
		} else {
			p = pathval();
		}
		for (sp = varlist.list ; sp ; sp = sp->next)
			setvareq(sp->text, VEXPORT|VSTACK);
		envp = environment();
		shellexec(argv, envp, p, cmdentry.u.index);
		/*NOTREACHED*/
	}
	goto out;

parent:	/* parent process gets here (if we forked) */
	if (mode == 0) {	/* argument to fork */
		INTOFF;
		exitstatus = waitforjob(jp);
		INTON;
	} else if (mode == 2) {
		backcmd->fd = pip[0];
		close(pip[1]);
		backcmd->jp = jp;
	}

out:
	if (lastarg)
		setvar("_", lastarg, 0);
	popstackmark(&smark);
}



/*
 * Search for a command.  This is called before we fork so that the
 * location of the command will be available in the parent as well as
 * the child.  The check for "goodname" is an overly conservative
 * check that the name will not be subject to expansion.
 */

STATIC void
prehash(n)
	union node *n;
	{
	struct cmdentry entry;

	if (n->type == NCMD && goodname(n->ncmd.args->narg.text))
		find_command(n->ncmd.args->narg.text, &entry, 0);
}



/*
 * Builtin commands.  Builtin commands whose functions are closely
 * tied to evaluation are implemented here.
 */

/*
 * No command given, or a bltin command with no arguments.  Set the
 * specified variables.
 */

bltincmd(argc, argv)  char **argv; {
	listsetvar(cmdenviron);
	return exitstatus;
}


/*
 * Handle break and continue commands.  Break, continue, and return are
 * all handled by setting the evalskip flag.  The evaluation routines
 * above all check this flag, and if it is set they start skipping
 * commands rather than executing them.  The variable skipcount is
 * the number of loops to break/continue, or the number of function
 * levels to return.  (The latter is always 1.)  It should probably
 * be an error to break out of more loops than exist, but it isn't
 * in the standard shell so we don't make it one here.
 */

breakcmd(argc, argv)  char **argv; {
	int n;

	n = 1;
	if (argc > 1)
		n = number(argv[1]);
	if (n > loopnest)
		n = loopnest;
	if (n > 0) {
		evalskip = (**argv == 'c')? SKIPCONT : SKIPBREAK;
		skipcount = n;
	}
	return 0;
}


/*
 * The return command.
 */

returncmd(argc, argv)  char **argv; {
	int ret;

	ret = exitstatus;
	if (argc > 1)
		ret = number(argv[1]);
	if (funcnest) {
		evalskip = SKIPFUNC;
		skipcount = 1;
	}
	return ret;
}


truecmd(argc, argv)  char **argv; {
	return strcmp(argv[0], "false") == 0 ? 1 : 0;
}


execcmd(argc, argv)  char **argv; {
	if (argc > 1) {
		iflag = 0;		/* exit on error */
		setinteractive(0);
#if JOBS
		jflag = 0;
		setjobctl(0);
#endif
		shellexec(argv + 1, environment(), pathval(), 0);

	}
	return 0;
}