var.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

	}
	if (*val == '=')
		tvar = str_nsave(var, val++ - var, ATEMP);
	else {
		/* Importing from original envirnment: must have an = */
		if (set & IMPORT)
			return NULL;
		tvar = (char *) var;
		val = NULL;
	}

	/* Prevent typeset from creating a local PATH/ENV/SHELL */
	if (Flag(FRESTRICTED) && (strcmp(tvar, "PATH") == 0
				  || strcmp(tvar, "ENV") == 0
				  || strcmp(tvar, "SHELL") == 0))
		errorf("%s: restricted", tvar);

	vp = (set&LOCAL) ? local(tvar, (set & LOCAL_COPY) ? TRUE : FALSE)
		: global(tvar);
	set &= ~(LOCAL|LOCAL_COPY);

	vpbase = (vp->flag & ARRAY) ? global(arrayname(var)) : vp;

	/* only allow export flag to be set.  at&t ksh allows any attribute to
	 * be changed, which means it can be truncated or modified
	 * (-L/-R/-Z/-i).
	 */
	if ((vpbase->flag&RDONLY)
	    && (val || clr || (set & ~EXPORT)))
		/* XXX check calls - is error here ok by POSIX? */
		errorf("%s: is read only", tvar);
	if (val)
		afree(tvar, ATEMP);

	/* most calls are with set/clr == 0 */
	if (set | clr) {
		int ok = 1;
		/* XXX if x[0] isn't set, there will be problems: need to have
		 * one copy of attributes for arrays...
		 */
		for (t = vpbase; t; t = t->u.array) {
			int fake_assign;
			char UNINITIALIZED(*s);
			char UNINITIALIZED(*free_me);

			fake_assign = (t->flag & ISSET) && (!val || t != vp)
				      && ((set & (UCASEV_AL|LCASEV|LJUST|RJUST|ZEROFIL))
					  || ((t->flag & INTEGER) && (clr & INTEGER))
					  || (!(t->flag & INTEGER) && (set & INTEGER)));
			if (fake_assign) {
				if (t->flag & INTEGER) {
					s = str_val(t);
					free_me = (char *) 0;
				} else {
					s = t->val.s + t->type;
					free_me = (t->flag & ALLOC) ? t->val.s
								  : (char *) 0;
				}
				t->flag &= ~ALLOC;
			}
			if (!(t->flag & INTEGER) && (set & INTEGER)) {
				t->type = 0;
				t->flag &= ~ALLOC;
			}
			t->flag = (t->flag | set) & ~clr;
			/* Don't change base if assignment is to be done,
			 * in case assignment fails.
			 */
			if ((set & INTEGER) && base > 0 && (!val || t != vp))
				t->type = base;
			if (set & (LJUST|RJUST|ZEROFIL))
				t->u2.field = field;
			if (fake_assign) {
				if (!setstr(t, s, KSH_RETURN_ERROR)) {
					/* Somewhat arbitrary action here:
					 * zap contents of varibale, but keep
					 * the flag settings.
					 */
					ok = 0;
					if (t->flag & INTEGER)
						t->flag &= ~ISSET;
					else {
						if (t->flag & ALLOC)
							afree((void*) t->val.s,
							      t->areap);
						t->flag &= ~(ISSET|ALLOC);
						t->type = 0;
					}
				}
				if (free_me)
					afree((void *) free_me, t->areap);
			}
		}
		if (!ok)
		    errorf(null);
	}

	if (val != NULL) {
		if (vp->flag&INTEGER) {
			/* do not zero base before assignment */
			setstr(vp, val, KSH_UNWIND_ERROR);
			/* Done after assignment to override default */
			if (base > 0)
				vp->type = base;
		} else
			/* setstr can't fail (readonly check already done) */
			setstr(vp, val, KSH_RETURN_ERROR);
	}

	/* only x[0] is ever exported, so use vpbase */
	if ((vpbase->flag&EXPORT) && !(vpbase->flag&INTEGER)
	    && vpbase->type == 0)
		export(vpbase, (vpbase->flag&ISSET) ? vpbase->val.s : null);

	return vp;
}

/* Unset a variable.  array_ref is set if there was an array reference in
 * the name lookup (eg, x[2]).
 */
void
unset(vp, array_ref)
	register struct tbl *vp;
	int array_ref;
{
	if (vp->flag & ALLOC)
		afree((void*)vp->val.s, vp->areap);
	if ((vp->flag & ARRAY) && !array_ref) {
		struct tbl *a, *tmp;

		/* Free up entire array */
		for (a = vp->u.array; a; ) {
			tmp = a;
			a = a->u.array;
			if (tmp->flag & ALLOC)
				afree((void *) tmp->val.s, tmp->areap);
			afree(tmp, tmp->areap);
		}
		vp->u.array = (struct tbl *) 0;
	}
	/* If foo[0] is being unset, the remainder of the array is kept... */
	vp->flag &= SPECIAL | (array_ref ? ARRAY|DEFINED : 0);
	if (vp->flag & SPECIAL)
		unsetspec(vp);	/* responsible for `unspecial'ing var */
}

/* return a pointer to the first char past a legal variable name (returns the
 * argument if there is no legal name, returns * a pointer to the terminating
 * null if whole string is legal).
 */
char *
skip_varname(s, aok)
	const char *s;
	int aok;
{
	int alen;

	if (s && letter(*s)) {
		while (*++s && letnum(*s))
			;
		if (aok && *s == '[' && (alen = array_ref_len(s)))
			s += alen;
	}
	return (char *) s;
}

/* Return a pointer to the first character past any legal variable name.  */
char *
skip_wdvarname(s, aok)
	const char *s;
	int aok;	/* skip array de-reference? */
{
	if (s[0] == CHAR && letter(s[1])) {
		do
			s += 2;
		while (s[0] == CHAR && letnum(s[1]));
		if (aok && s[0] == CHAR && s[1] == '[') {
			/* skip possible array de-reference */
			const char *p = s;
			char c;
			int depth = 0;

			while (1) {
				if (p[0] != CHAR)
					break;
				c = p[1];
				p += 2;
				if (c == '[')
					depth++;
				else if (c == ']' && --depth == 0) {
					s = p;
					break;
				}
			}
		}
	}
	return (char *) s;
}

/* Check if coded string s is a variable name */
int
is_wdvarname(s, aok)
	const char *s;
	int aok;
{
	char *p = skip_wdvarname(s, aok);

	return p != s && p[0] == EOS;
}

/* Check if coded string s is a variable assignment */
int
is_wdvarassign(s)
	const char *s;
{
	char *p = skip_wdvarname(s, TRUE);

	return p != s && p[0] == CHAR && p[1] == '=';
}

/*
 * Make the exported environment from the exported names in the dictionary.
 */
char **
makenv()
{
	struct block *l = e->loc;
	XPtrV env;
	register struct tbl *vp, **vpp;
	register int i;

	XPinit(env, 64);
	for (l = e->loc; l != NULL; l = l->next)
		for (vpp = l->vars.tbls, i = l->vars.size; --i >= 0; )
			if ((vp = *vpp++) != NULL
			    && (vp->flag&(ISSET|EXPORT)) == (ISSET|EXPORT)) {
				register struct block *l2;
				register struct tbl *vp2;
				unsigned h = hash(vp->name);

				/* unexport any redefined instances */
				for (l2 = l->next; l2 != NULL; l2 = l2->next) {
					vp2 = tsearch(&l2->vars, vp->name, h);
					if (vp2 != NULL)
						vp2->flag &= ~EXPORT;
				}
				if ((vp->flag&INTEGER)) {
					/* integer to string */
					char *val;
					val = str_val(vp);
					vp->flag &= ~(INTEGER|RDONLY);
					/* setstr can't fail here */
					setstr(vp, val, KSH_RETURN_ERROR);
				}
				XPput(env, vp->val.s);
			}
	XPput(env, NULL);
	return (char **) XPclose(env);
}

/*
 * Called after a fork in parent to bump the random number generator.
 * Done to ensure children will not get the same random number sequence
 * if the parent doesn't use $RANDOM.
 */
void
change_random()
{
    rand();
}

/*
 * handle special variables with side effects - PATH, SECONDS.
 */

/* Test if name is a special parameter */
static int
special(name)
	register const char * name;
{
	register struct tbl *tp;

	tp = tsearch(&specials, name, hash(name));
	return tp && (tp->flag & ISSET) ? tp->type : V_NONE;
}

/* Make a variable non-special */
static void
unspecial(name)
	register const char * name;
{
	register struct tbl *tp;

	tp = tsearch(&specials, name, hash(name));
	if (tp)
		tdelete(tp);
}

#ifdef KSH
static	time_t	seconds;		/* time SECONDS last set */
#endif /* KSH */
static	int	user_lineno;		/* what user set $LINENO to */

static void
getspec(vp)
	register struct tbl *vp;
{
	switch (special(vp->name)) {
#ifdef KSH
	  case V_SECONDS:
		vp->flag &= ~SPECIAL;
		/* On start up the value of SECONDS is used before seconds
		 * has been set - don't do anything in this case
		 * (see initcoms[] in main.c).
		 */
		if (vp->flag & ISSET)
			setint(vp, (long) (time((time_t *)0) - seconds));
		vp->flag |= SPECIAL;
		break;
	  case V_RANDOM:
		vp->flag &= ~SPECIAL;
		setint(vp, (long) (rand() & 0x7fff));
		vp->flag |= SPECIAL;
		break;
#endif /* KSH */
#ifdef HISTORY
	  case V_HISTSIZE:
		vp->flag &= ~SPECIAL;
		setint(vp, (long) histsize);
		vp->flag |= SPECIAL;
		break;
#endif /* HISTORY */
	  case V_OPTIND:
		vp->flag &= ~SPECIAL;
		setint(vp, (long) user_opt.uoptind);
		vp->flag |= SPECIAL;
		break;
	  case V_LINENO:
		vp->flag &= ~SPECIAL;
		setint(vp, (long) current_lineno + user_lineno);
		vp->flag |= SPECIAL;
		break;
	}
}

static void
setspec(vp)
	register struct tbl *vp;
{
	char *s;

	switch (special(vp->name)) {
	  case V_PATH:
		if (path)
			afree(path, APERM);
		path = str_save(str_val(vp), APERM);
		flushcom(1);	/* clear tracked aliases */
		break;
	  case V_IFS:
		setctypes(s = str_val(vp), C_IFS);
		ifs0 = *s;
		break;
	  case V_OPTIND:
		vp->flag &= ~SPECIAL;
		getopts_reset((int) intval(vp));
		vp->flag |= SPECIAL;
		break;
	  case V_POSIXLY_CORRECT:
		change_flag(FPOSIX, OF_SPECIAL, 1);
		break;
	  case V_TMPDIR:
		if (tmpdir) {
			afree(tmpdir, APERM);
			tmpdir = (char *) 0;
		}
		/* Use tmpdir iff it is an absolute path, is writable and
		 * searchable and is a directory...
		 */
		{
			struct stat statb;
			s = str_val(vp);
			if (ISABSPATH(s) && eaccess(s, W_OK|X_OK) == 0
			    && stat(s, &statb) == 0 && S_ISDIR(statb.st_mode))
				tmpdir = str_save(s, APERM);
		}
		break;
#ifdef HISTORY
	  case V_HISTSIZE:
		vp->flag &= ~SPECIAL;
		sethistsize((int) intval(vp));
		vp->flag |= SPECIAL;
		break;
	  case V_HISTFILE:
		sethistfile(str_val(vp));
		break;
#endif /* HISTORY */
#ifdef EDIT
	  case V_VISUAL:
		set_editmode(str_val(vp));
		break;
	  case V_EDITOR:
		if (!(global("VISUAL")->flag & ISSET))
			set_editmode(str_val(vp));
		break;
	  case V_COLUMNS:
		if ((x_cols = intval(vp)) <= MIN_COLS)
			x_cols = MIN_COLS;
		break;
#endif /* EDIT */
#ifdef KSH
	  case V_MAIL:
		mbset(str_val(vp));
		break;
	  case V_MAILPATH:
		mpset(str_val(vp));
		break;
	  case V_MAILCHECK:
		vp->flag &= ~SPECIAL;
		mcset(intval(vp));
		vp->flag |= SPECIAL;
		break;
	  case V_RANDOM:
		vp->flag &= ~SPECIAL;
		srand((unsigned int)intval(vp));
		vp->flag |= SPECIAL;
		break;
	  case V_SECONDS:
		vp->flag &= ~SPECIAL;
		seconds = time((time_t*) 0) - intval(vp);
		vp->flag |= SPECIAL;
		break;
	  case V_TMOUT:
		/* at&t ksh seems to do this (only listen if integer) */
		if (vp->flag & INTEGER)
			ksh_tmout = vp->val.i >= 0 ? vp->val.i : 0;
		break;
#endif /* KSH */
	  case V_LINENO:
		vp->flag &= ~SPECIAL;
		/* The -1 is because line numbering starts at 1. */
		user_lineno = (unsigned int) intval(vp) - current_lineno - 1;
		vp->flag |= SPECIAL;
		break;
	}
}

static void
unsetspec(vp)
	register struct tbl *vp;
{
	switch (special(vp->name)) {
	  case V_PATH:
		if (path)
			afree(path, APERM);
		path = str_save(def_path, APERM);
		flushcom(1);	/* clear tracked aliases */
		break;
	  case V_IFS:
		setctypes(" \t\n", C_IFS);
		ifs0 = ' ';
		break;
	  case V_TMPDIR:
		/* should not become unspecial */
		if (tmpdir) {
			afree(tmpdir, APERM);
			tmpdir = (char *) 0;
		}
		break;
#ifdef KSH
	  case V_MAIL:
		mbset((char *) 0);
		break;
	  case V_MAILPATH:
		mpset((char *) 0);
		break;
#endif /* KSH */

	  case V_LINENO:
#ifdef KSH
	  case V_MAILCHECK:	/* at&t ksh leaves previous value in place */
	  case V_RANDOM:
	  case V_SECONDS:
	  case V_TMOUT:		/* at&t ksh leaves previous value in place */
#endif /* KSH */
		unspecial(vp->name);
		break;

	  /* at&t ksh man page says OPTIND, OPTARG and _ lose special meaning,
	   * but OPTARG does not (still set by getopts) and _ is also still
	   * set in various places.
	   * Don't know what at&t does for:
	   *		MAIL, MAILPATH, HISTSIZE, HISTFILE,
	   * Unsetting these in at&t ksh does not loose the `specialness':
	   *    no effect: IFS, COLUMNS, PATH, TMPDIR,
	   *		VISUAL, EDITOR,
	   * pdkshisms: no effect:
	   *		POSIXLY_CORRECT (use set +o posix instead)
	   */
	}
}

/*
 * Search for (and possibly create) a table entry starting with
 * vp, indexed by val.
 */
static struct tbl *
arraysearch(vp, val)
	struct tbl *vp;
	int val;
{
	struct tbl *prev, *curr, *new;

	vp->flag |= ARRAY|DEFINED;

	/* The table entry is always [0] */
	if (val == 0) {
		vp->index = 0;
		return vp;
	}
	prev = vp;
	curr = vp->u.array;
	while (curr && curr->index < val) {
		prev = curr;
		curr = curr->u.array;
	}
	if (curr && curr->index == val) {
		if (curr->flag&ISSET)
			return curr;
		else
			new = curr;
	} else
		new = (struct tbl *)alloc(sizeof(struct tbl)+strlen(vp->name)+1, vp->areap);
	strcpy(new->name, vp->name);
	new->flag = vp->flag & ~(ALLOC|DEFINED|ISSET|SPECIAL);
	new->type = vp->type;
	new->areap = vp->areap;
	new->u2.field = vp->u2.field;
	new->index = val;
	if (curr != new) {		/* not reusing old array entry */
		prev->u.array = new;
		new->u.array = curr;
	}
	return new;
}

/* Return the length of an array reference (eg, [1+2]) - cp is assumed
 * to point to the open bracket.  Returns 0 if there is no matching closing
 * bracket.
 */
int
array_ref_len(cp)
	const char *cp;
{
	const char *s = cp;
	int c;
	int depth = 0;

	while ((c = *s++) && (c != ']' || --depth))
		if (c == '[')
			depth++;
	if (!c)
		return 0;
	return s - cp;
}

/*
 * Make a copy of the base of an array name
 */
char *
arrayname(str)
	const char *str;
{
	const char *p;

	if ((p = strchr(str, '[')) == 0)
		/* Shouldn't happen, but why worry? */
		return (char *) str;

	return str_nsave(str, p - str, ATEMP);
}

/* Set (or overwrite, if !reset) the array variable var to the values in vals.
 */
void
set_array(var, reset, vals)
	const char *var;
	int reset;
	char **vals;
{
	struct tbl *vp, *vq;
	int i;

	/* to get local array, use "typeset foo; set -A foo" */
	vp = global(var);

	/* Note: at&t ksh allows set -A but not set +A of a read-only var */
	if ((vp->flag&RDONLY))
		errorf("%s: is read only", var);
	/* This code is quite non-optimal */
	if (reset > 0)
		/* trash existing values and attributes */
		unset(vp, 0);
	/* todo: would be nice for assignment to completely succeed or
	 * completely fail.  Only really effects integer arrays:
	 * evaluation of some of vals[] may fail...
	 */
	for (i = 0; vals[i]; i++) {
		vq = arraysearch(vp, i);
		/* would be nice to deal with errors here... (see above) */
		setstr(vq, vals[i], KSH_RETURN_ERROR);
	}
}