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

/*
 * execute command tree
 */

#include "sh.h"
#include "c_test.h"
#include <ctype.h>
#include "ksh_stat.h"

/* Does ps4 get parameter substitutions done? */
#ifdef KSH
# define PS4_SUBSTITUTE(s)	substitute((s), 0)
#else
# define PS4_SUBSTITUTE(s)	(s)
#endif /* KSH */

static int	comexec	 ARGS((struct op *t, struct tbl *volatile tp, char **ap,
			      int volatile flags));
static void	scriptexec ARGS((struct op *tp, char **ap));
static int	call_builtin ARGS((struct tbl *tp, char **wp));
static int	iosetup ARGS((struct ioword *iop, struct tbl *tp));
static int	herein ARGS((const char *content, int sub));
#ifdef KSH
static char 	*do_selectargs ARGS((char **ap, bool_t print_menu));
#endif /* KSH */
#ifdef KSH
static int	dbteste_isa ARGS((Test_env *te, Test_meta meta));
static const char *dbteste_getopnd ARGS((Test_env *te, Test_op op,
					 int do_eval));
static int	dbteste_eval ARGS((Test_env *te, Test_op op, const char *opnd1,
				const char *opnd2, int do_eval));
static void	dbteste_error ARGS((Test_env *te, int offset, const char *msg));
#endif /* KSH */
#ifdef OS2
static int	search_access1 ARGS((const char *path, int mode, int *errnop));
#endif /* OS2 */


/*
 * handle systems that don't have F_SETFD
 */
#ifndef F_SETFD
# ifndef MAXFD
#   define  MAXFD 64
# endif
/* a bit field would be smaller, but this will work */
static char clexec_tab[MAXFD+1];
#endif

/*
 * we now use this function always.
 */
int
fd_clexec(fd)
    int fd;
{
#ifndef F_SETFD
	if (fd >= 0 && fd < sizeof(clexec_tab)) {
		clexec_tab[fd] = 1;
		return 0;
	}
	return -1;
#else
	return fcntl(fd, F_SETFD, 1);
#endif
}


/*
 * execute command tree
 */
int
execute(t, flags)
	struct op * volatile t;
	volatile int flags;	/* if XEXEC don't fork */
{
	int i;
	volatile int rv = 0;
	int pv[2];
	char ** volatile ap;
	char *s, *cp;
	struct ioword **iowp;
	struct tbl *tp = NULL;

	if (t == NULL)
		return 0;

	/* Is this the end of a pipeline?  If so, we want to evaluate the
	 * command arguments
	bool_t eval_done = FALSE;
	if ((flags&XFORK) && !(flags&XEXEC) && (flags&XPCLOSE)) {
		eval_done = TRUE;
		tp = eval_execute_args(t, &ap);
	}
	 */
	if ((flags&XFORK) && !(flags&XEXEC) && t->type != TPIPE)
		return exchild(t, flags & ~XTIME, -1); /* run in sub-process */

	newenv(E_EXEC);
	if (trap)
		runtraps(0);
 
	if (t->type == TCOM) {
		/* Clear subst_exstat before argument expansion.  Used by
		 * null commands (see comexec() and c_eval()) and by c_set().
		 */
		subst_exstat = 0;

		current_lineno = t->lineno;	/* for $LINENO */

		/* POSIX says expand command words first, then redirections,
		 * and assignments last..
		 */
		ap = eval(t->args, t->u.evalflags | DOBLANK | DOGLOB | DOTILDE);
		if (flags & XTIME)
			/* Allow option parsing (bizarre, but POSIX) */
			timex_hook(t, &ap);
		if (Flag(FXTRACE) && ap[0]) {
			shf_fprintf(shl_out, "%s",
				PS4_SUBSTITUTE(str_val(global("PS4"))));
			for (i = 0; ap[i]; i++)
				shf_fprintf(shl_out, "%s%s", ap[i],
					ap[i + 1] ? space : newline);
			shf_flush(shl_out);
		}
		if (ap[0])
			tp = findcom(ap[0], FC_BI|FC_FUNC);
	}
	flags &= ~XTIME;

	if (t->ioact != NULL || t->type == TPIPE || t->type == TCOPROC) {
		e->savefd = (short *) alloc(sizeofN(short, NUFILE), ATEMP);
		/* initialize to not redirected */
		memset(e->savefd, 0, sizeofN(short, NUFILE));
	}

	/* do redirection, to be restored in quitenv() */
	if (t->ioact != NULL)
		for (iowp = t->ioact; *iowp != NULL; iowp++) {
			if (iosetup(*iowp, tp) < 0) {
				exstat = rv = 1;
				/* Redirection failures for special commands
				 * cause (non-interactive) shell to exit.
				 */
				if (tp && tp->type == CSHELL
				    && (tp->flag & SPEC_BI))
					errorf(null);
				/* Deal with FERREXIT, quitenv(), etc. */
				goto Break;
			}
		}
	
	switch(t->type) {
	  case TCOM:
		rv = comexec(t, tp, ap, flags);
		break;

	  case TPAREN:
		rv = execute(t->left, flags|XFORK);
		break;

	  case TPIPE:
		flags |= XFORK;
		flags &= ~XEXEC;
		e->savefd[0] = savefd(0, 0);
		(void) ksh_dup2(e->savefd[0], 0, FALSE); /* stdin of first */
		e->savefd[1] = savefd(1, 0);
		while (t->type == TPIPE) {
			openpipe(pv);
			(void) ksh_dup2(pv[1], 1, FALSE); /* stdout of curr */
			/* Let exchild() close pv[0] in child
			 * (if this isn't done, commands like
			 *    (: ; cat /etc/termcap) | sleep 1
			 *  will hang forever).
			 */
			exchild(t->left, flags|XPIPEO|XCCLOSE, pv[0]);
			(void) ksh_dup2(pv[0], 0, FALSE); /* stdin of next */
			closepipe(pv);
			flags |= XPIPEI;
			t = t->right;
		}
		restfd(1, e->savefd[1]); /* stdout of last */
		e->savefd[1] = 0; /* no need to re-restore this */
		/* Let exchild() close 0 in parent, after fork, before wait */
		i = exchild(t, flags|XPCLOSE, 0);
		if (!(flags&XBGND) && !(flags&XXCOM))
			rv = i;
		break;

	  case TLIST:
		while (t->type == TLIST) {
			execute(t->left, flags & XERROK);
			t = t->right;
		}
		rv = execute(t, flags & XERROK);
		break;

#ifdef KSH
	  case TCOPROC:
	  {
# ifdef JOB_SIGS
		sigset_t	omask;
# endif /* JOB_SIGS */

# ifdef JOB_SIGS
		/* Block sigchild as we are using things changed in the
		 * signal handler
		 */
		sigprocmask(SIG_BLOCK, &sm_sigchld, &omask);
		e->type = E_ERRH;
		i = ksh_sigsetjmp(e->jbuf, 0);
		if (i) {
			sigprocmask(SIG_SETMASK, &omask, (sigset_t *) 0);
			quitenv();
			unwind(i);
			/*NOTREACHED*/
		}
# endif /* JOB_SIGS */
		/* Already have a (live) co-process? */
		if (coproc.job && coproc.write >= 0)
			errorf("coprocess already exists");

		/* Can we re-use the existing co-process pipe? */
		coproc_cleanup(TRUE);

		/* do this before opening pipes, in case these fail */
		e->savefd[0] = savefd(0, 0);
		e->savefd[1] = savefd(1, 0);

		openpipe(pv);
		ksh_dup2(pv[0], 0, FALSE);
		close(pv[0]);
		coproc.write = pv[1];
		coproc.job = (void *) 0;

		if (coproc.readw >= 0)
			ksh_dup2(coproc.readw, 1, FALSE);
		else {
			openpipe(pv);
			coproc.read = pv[0];
			ksh_dup2(pv[1], 1, FALSE);
			coproc.readw = pv[1];	 /* closed before first read */
			coproc.njobs = 0;
			/* create new coprocess id */
			++coproc.id;
		}
# ifdef JOB_SIGS
		sigprocmask(SIG_SETMASK, &omask, (sigset_t *) 0);
		e->type = E_EXEC; /* no more need for error handler */
# endif /* JOB_SIGS */

		/* exchild() closes coproc.* in child after fork,
		 * will also increment coproc.njobs when the
		 * job is actually created.
		 */
		flags &= ~XEXEC;
		exchild(t->left, flags|XBGND|XFORK|XCOPROC|XCCLOSE,
			coproc.readw);
		break;
	  }
#endif /* KSH */

	  case TASYNC:
		/* XXX non-optimal, I think - "(foo &)", forks for (),
		 * forks again for async...  parent should optimize
		 * this to "foo &"...
		 */
		rv = execute(t->left, (flags&~XEXEC)|XBGND|XFORK);
		break;

	  case TOR:
	  case TAND:
		rv = execute(t->left, XERROK);
		if (t->right != NULL && (rv == 0) == (t->type == TAND))
			rv = execute(t->right, flags & XERROK);
		else
			flags |= XERROK;
		break;

	  case TBANG:
		rv = !execute(t->right, XERROK);
		break;

#ifdef KSH
	  case TDBRACKET:
	    {
		Test_env te;

		te.flags = TEF_DBRACKET;
		te.pos.wp = t->args;
		te.isa = dbteste_isa;
		te.getopnd = dbteste_getopnd;
		te.eval = dbteste_eval;
		te.error = dbteste_error;

		rv = test_parse(&te);
		break;
	    }
#endif /* KSH */

	  case TFOR:
#ifdef KSH
	  case TSELECT:
	    {
		volatile bool_t is_first = TRUE;
#endif /* KSH */
		ap = (t->vars != NULL) ?
			  eval(t->vars, DOBLANK|DOGLOB|DOTILDE)
			: e->loc->argv + 1;
		e->type = E_LOOP;
		while (1) {
			i = ksh_sigsetjmp(e->jbuf, 0);
			if (!i)
				break;
			if ((e->flags&EF_BRKCONT_PASS)
			    || (i != LBREAK && i != LCONTIN))
			{
				quitenv();
				unwind(i);
			} else if (i == LBREAK) {
				rv = 0;
				goto Break;
			}
		}
		rv = 0; /* in case of a continue */
		if (t->type == TFOR) {
			while (*ap != NULL) {
				setstr(global(t->str), *ap++, KSH_UNWIND_ERROR);
				rv = execute(t->left, flags & XERROK);
			}
		}
#ifdef KSH
		else { /* TSELECT */
			for (;;) {
				if (!(cp = do_selectargs(ap, is_first))) {
					rv = 1;
					break;
				}
				is_first = FALSE;
				setstr(global(t->str), cp, KSH_UNWIND_ERROR);
				rv = execute(t->left, flags & XERROK);
			}
		}
	    }
#endif /* KSH */
		break;

	  case TWHILE:
	  case TUNTIL:
		e->type = E_LOOP;
		while (1) {
			i = ksh_sigsetjmp(e->jbuf, 0);
			if (!i)
				break;
			if ((e->flags&EF_BRKCONT_PASS)
			    || (i != LBREAK && i != LCONTIN))
			{
				quitenv();
				unwind(i);
			} else if (i == LBREAK) {
				rv = 0;
				goto Break;
			}
		}
		rv = 0; /* in case of a continue */
		while ((execute(t->left, XERROK) == 0) == (t->type == TWHILE))
			rv = execute(t->right, flags & XERROK);
		break;

	  case TIF:
	  case TELIF:
		if (t->right == NULL)
			break;	/* should be error */
		rv = execute(t->left, XERROK) == 0 ?
			execute(t->right->left, flags & XERROK) :
			execute(t->right->right, flags & XERROK);
		break;

	  case TCASE:
		cp = evalstr(t->str, DOTILDE);
		for (t = t->left; t != NULL && t->type == TPAT; t = t->right)
		    for (ap = t->vars; *ap; ap++)
			if ((s = evalstr(*ap, DOTILDE|DOPAT))
			    && gmatch(cp, s, FALSE))
				goto Found;
		break;
	  Found:
		rv = execute(t->left, flags & XERROK);
		break;

	  case TBRACE:
		rv = execute(t->left, flags & XERROK);
		break;

	  case TFUNCT:
		rv = define(t->str, t);
		break;

	  case TTIME:
		/* Clear XEXEC so nested execute() call doesn't exit
		 * (allows "ls -l | time grep foo").
		 */
		rv = timex(t, flags & ~XEXEC);
		break;

	  case TEXEC:		/* an eval'd TCOM */
		s = t->args[0];
		ap = makenv();
#ifndef F_SETFD
		for (i = 0; i < sizeof(clexec_tab); i++)
			if (clexec_tab[i]) {
				close(i);
				clexec_tab[i] = 0;
			}
#endif
		restoresigs();
		cleanup_proc_env();
		/* XINTACT bit is for OS2 */
		ksh_execve(t->str, t->args, ap, (flags & XINTACT) ? 1 : 0);
		if (errno == ENOEXEC)
			scriptexec(t, ap);
		else
			errorf("%s: %s", s, strerror(errno));
	}
    Break:
	exstat = rv;

	quitenv();		/* restores IO */
	if ((flags&XEXEC))
		unwind(LEXIT);	/* exit child */
	if (rv != 0 && !(flags & XERROK)) {
		if (Flag(FERREXIT))
			unwind(LERROR);
		trapsig(SIGERR_);
	}
	return rv;
}

/*
 * execute simple command
 */

static int
comexec(t, tp, ap, flags)
	struct op *t;
	struct tbl *volatile tp;
	register char **ap;
	int volatile flags;
{
	int i;
	int rv = 0;
	register char *cp;
	register char **lastp;
	static struct op texec; /* Must be static (XXX but why?) */
	int type_flags;
	int keepasn_ok;
	int fcflags = FC_BI|FC_FUNC|FC_PATH;

#ifdef KSH
	/* snag the last argument for $_ XXX not the same as at&t ksh,
	 * which only seems to set $_ after a newline (but not in
	 * functions/dot scripts, but in interactive and scipt) -
	 * perhaps save last arg here and set it in shell()?.
	 */
	if (Flag(FTALKING) && *(lastp = ap)) {
		while (*++lastp)
			;
		/* setstr() can't fail here */
		setstr(typeset("_", LOCAL, 0, INTEGER, 0), *--lastp,
		       KSH_RETURN_ERROR);
	}
#endif /* KSH */

	/* Deal with the shell builtins builtin, exec and command since
	 * they can be followed by other commands.  This must be done before
	 * we know if we should create a local block, which must be done
	 * before we can do a path search (in case the assignments change
	 * PATH).
	 * Odd cases:
	 *   FOO=bar exec > /dev/null		FOO is kept but not exported
	 *   FOO=bar exec foobar		FOO is exported
	 *   FOO=bar command exec > /dev/null	FOO is neither kept nor exported
	 *   FOO=bar command			FOO is neither kept nor exported
	 *   PATH=... foobar			use new PATH in foobar search
	 */
	keepasn_ok = 1;
	while (tp && tp->type == CSHELL) {
		fcflags = FC_BI|FC_FUNC|FC_PATH;/* undo effects of command */
		if (tp->val.f == c_builtin) {
			if ((cp = *++ap) == NULL) {
				tp = NULL;
				break;
			}
			tp = findcom(cp, FC_BI);
			if (tp == NULL)
				errorf("builtin: %s: not a builtin", cp);
			continue;
		} else if (tp->val.f == c_exec) {
			if (ap[1] == NULL)
				break;
			ap++;
			flags |= XEXEC;
		} else if (tp->val.f == c_command) {
			int optc, saw_p = 0;

			/* Ugly dealing with options in two places (here and
			 * in c_command(), but such is life)
			 */
			ksh_getopt_reset(&builtin_opt, 0);
			while ((optc = ksh_getopt(ap, &builtin_opt, ":p"))
									== 'p')
				saw_p = 1;
			if (optc != EOF)
				break;	/* command -vV or something */
			/* don't look for functions */
			fcflags = FC_BI|FC_PATH;
			if (saw_p) {
				if (Flag(FRESTRICTED)) {
					warningf(TRUE,
						"command -p: restricted");
					rv = 1;
					goto Leave;
				}
				fcflags |= FC_DEFPATH;
			}
			ap += builtin_opt.optind;
			/* POSIX says special builtins lose their status
			 * if accessed using command.
			 */
			keepasn_ok = 0;
			if (!ap[0]) {
				/* ensure command with no args exits with 0 */
				subst_exstat = 0;
				break;
			}
		} else
			break;
		tp = findcom(ap[0], fcflags & (FC_BI|FC_FUNC));
	}
	if (keepasn_ok && (!ap[0] || (tp && (tp->flag & KEEPASN))))
		type_flags = 0;
	else {
		/* create new variable/function block */
		newblock();
		/* ksh functions don't keep assignments, POSIX functions do. */
		if (keepasn_ok && tp && tp->type == CFUNC
		    && !(tp->flag & FKSH))
			type_flags = 0;
		else
			type_flags = LOCAL|LOCAL_COPY|EXPORT;
	}
	if (Flag(FEXPORT))
		type_flags |= EXPORT;
	for (i = 0; t->vars[i]; i++) {
		cp = evalstr(t->vars[i], DOASNTILDE);
		if (Flag(FXTRACE)) {
			if (i == 0)
				shf_fprintf(shl_out, "%s",
					PS4_SUBSTITUTE(str_val(global("PS4"))));
			shf_fprintf(shl_out, "%s%s", cp,
				t->vars[i + 1] ? space : newline);
			if (!t->vars[i + 1])
				shf_flush(shl_out);