expand.c

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	case VSTRIMLEFT:
		for (loc = startp; loc < str; loc++) {
			c = *loc;
			*loc = '\0';
			if (patmatch(str, startp, varflags & VSQUOTE))
				goto recordleft;
			*loc = c;
			if ((varflags & VSQUOTE) && *loc == CTLESC)
			        loc++;
		}
		return 0;

	case VSTRIMLEFTMAX:
		for (loc = str - 1; loc >= startp;) {
			c = *loc;
			*loc = '\0';
			if (patmatch(str, startp, varflags & VSQUOTE))
				goto recordleft;
			*loc = c;
			loc--;
			if ((varflags & VSQUOTE) && loc > startp &&
			    *(loc - 1) == CTLESC) {
				for (q = startp; q < loc; q++)
					if (*q == CTLESC)
						q++;
				if (q > loc)
					loc--;
			}
		}
		return 0;

	case VSTRIMRIGHT:
	        for (loc = str - 1; loc >= startp;) {
			if (patmatch(str, loc, varflags & VSQUOTE))
				goto recordright;
			loc--;
			if ((varflags & VSQUOTE) && loc > startp &&
			    *(loc - 1) == CTLESC) { 
				for (q = startp; q < loc; q++)
					if (*q == CTLESC)
						q++;
				if (q > loc)
					loc--;
			}
		}
		return 0;

	case VSTRIMRIGHTMAX:
		for (loc = startp; loc < str - 1; loc++) {
			if (patmatch(str, loc, varflags & VSQUOTE))
				goto recordright;
			if ((varflags & VSQUOTE) && *loc == CTLESC)
			        loc++;
		}
		return 0;

	default:
		abort();
	}

recordleft:
	*loc = c;
	amount = ((str - 1) - (loc - startp)) - expdest;
	STADJUST(amount, expdest);
	while (loc != str - 1)
		*startp++ = *loc++;
	return 1;

recordright:
	amount = loc - expdest;
	STADJUST(amount, expdest);
	STPUTC('\0', expdest);
	STADJUST(-1, expdest);
	return 1;
}


/*
 * Expand a variable, and return a pointer to the next character in the
 * input string.
 */

STATIC char *
evalvar(char *p, int flag)
{
	int subtype;
	int varflags;
	char *var;
	char *val;
	int patloc;
	int c;
	int set;
	int special;
	int startloc;
	int varlen;
	int apply_ifs;
	int quotes = flag & (EXP_FULL | EXP_CASE);

	varflags = (unsigned char)*p++;
	subtype = varflags & VSTYPE;
	var = p;
	special = !is_name(*p);
	p = strchr(p, '=') + 1;

again: /* jump here after setting a variable with ${var=text} */
	if (special) {
		set = varisset(var, varflags & VSNUL);
		val = NULL;
	} else {
		val = lookupvar(var);
		if (val == NULL || ((varflags & VSNUL) && val[0] == '\0')) {
			val = NULL;
			set = 0;
		} else
			set = 1;
	}

	varlen = 0;
	startloc = expdest - stackblock();

	if (!set && uflag) {
		switch (subtype) {
		case VSNORMAL:
		case VSTRIMLEFT:
		case VSTRIMLEFTMAX:
		case VSTRIMRIGHT:
		case VSTRIMRIGHTMAX:
		case VSLENGTH:
			error("%.*s: parameter not set", p - var - 1, var);
			/* NOTREACHED */
		}
	}

	if (set && subtype != VSPLUS) {
		/* insert the value of the variable */
		if (special) {
			varvalue(var, varflags & VSQUOTE, subtype, flag);
			if (subtype == VSLENGTH) {
				varlen = expdest - stackblock() - startloc;
				STADJUST(-varlen, expdest);
			}
		} else {
			char const *syntax = (varflags & VSQUOTE) ? DQSYNTAX
								  : BASESYNTAX;

			if (subtype == VSLENGTH) {
				for (;*val; val++)
					varlen++;
			} else {
				while (*val) {
					if (quotes && syntax[(int)*val] == CCTL)
						STPUTC(CTLESC, expdest);
					STPUTC(*val++, expdest);
				}

			}
		}
	}


	apply_ifs = ((varflags & VSQUOTE) == 0 ||
		(*var == '@' && shellparam.nparam != 1));

	switch (subtype) {
	case VSLENGTH:
		expdest = cvtnum(varlen, expdest);
		break;

	case VSNORMAL:
		break;

	case VSPLUS:
		set = !set;
		/* FALLTHROUGH */
	case VSMINUS:
		if (!set) {
		        argstr(p, flag | (apply_ifs ? EXP_IFS_SPLIT : 0));
			/*
			 * ${x-a b c} doesn't get split, but removing the
			 * 'apply_ifs = 0' apparantly breaks ${1+"$@"}..
			 * ${x-'a b' c} should generate 2 args.
			 */
			/* We should have marked stuff already */
			apply_ifs = 0;
		}
		break;

	case VSTRIMLEFT:
	case VSTRIMLEFTMAX:
	case VSTRIMRIGHT:
	case VSTRIMRIGHTMAX:
		if (!set)
			break;
		/*
		 * Terminate the string and start recording the pattern
		 * right after it
		 */
		STPUTC('\0', expdest);
		patloc = expdest - stackblock();
		if (subevalvar(p, NULL, patloc, subtype,
			       startloc, varflags) == 0) {
			int amount = (expdest - stackblock() - patloc) + 1;
			STADJUST(-amount, expdest);
		}
		/* Remove any recorded regions beyond start of variable */
		removerecordregions(startloc);
		apply_ifs = 1;
		break;

	case VSASSIGN:
	case VSQUESTION:
		if (set)
			break;
		if (subevalvar(p, var, 0, subtype, startloc, varflags)) {
			varflags &= ~VSNUL;
			/* 
			 * Remove any recorded regions beyond 
			 * start of variable 
			 */
			removerecordregions(startloc);
			goto again;
		}
		apply_ifs = 0;
		break;

	default:
		abort();
	}

	if (apply_ifs)
		recordregion(startloc, expdest - stackblock(),
			     varflags & VSQUOTE);

	if (subtype != VSNORMAL) {	/* skip to end of alternative */
		int nesting = 1;
		for (;;) {
			if ((c = *p++) == CTLESC)
				p++;
			else if (c == CTLBACKQ || c == (CTLBACKQ|CTLQUOTE)) {
				if (set)
					argbackq = argbackq->next;
			} else if (c == CTLVAR) {
				if ((*p++ & VSTYPE) != VSNORMAL)
					nesting++;
			} else if (c == CTLENDVAR) {
				if (--nesting == 0)
					break;
			}
		}
	}
	return p;
}



/*
 * Test whether a specialized variable is set.
 */

STATIC int
varisset(char *name, int nulok)
{
	if (*name == '!')
		return backgndpid != -1;
	else if (*name == '@' || *name == '*') {
		if (*shellparam.p == NULL)
			return 0;

		if (nulok) {
			char **av;

			for (av = shellparam.p; *av; av++)
				if (**av != '\0')
					return 1;
			return 0;
		}
	} else if (is_digit(*name)) {
		char *ap;
		int num = atoi(name);

		if (num > shellparam.nparam)
			return 0;

		if (num == 0)
			ap = arg0;
		else
			ap = shellparam.p[num - 1];

		if (nulok && (ap == NULL || *ap == '\0'))
			return 0;
	}
	return 1;
}



/*
 * Add the value of a specialized variable to the stack string.
 */

STATIC void
varvalue(char *name, int quoted, int subtype, int flag)
{
	int num;
	char *p;
	int i;
	char sep;
	char **ap;
	char const *syntax;

#define STRTODEST(p) \
	do {\
	if (flag & (EXP_FULL | EXP_CASE) && subtype != VSLENGTH) { \
		syntax = quoted? DQSYNTAX : BASESYNTAX; \
		while (*p) { \
			if (syntax[(int)*p] == CCTL) \
				STPUTC(CTLESC, expdest); \
			STPUTC(*p++, expdest); \
		} \
	} else \
		while (*p) \
			STPUTC(*p++, expdest); \
	} while (0)


	switch (*name) {
	case '$':
		num = rootpid;
		goto numvar;
	case '?':
		num = exitstatus;
		goto numvar;
	case '#':
		num = shellparam.nparam;
		goto numvar;
	case '!':
		num = backgndpid;
numvar:
		expdest = cvtnum(num, expdest);
		break;
	case '-':
		for (i = 0; optlist[i].name; i++) {
			if (optlist[i].val)
				STPUTC(optlist[i].letter, expdest);
		}
		break;
	case '@':
		if (flag & EXP_FULL && quoted) {
			for (ap = shellparam.p ; (p = *ap++) != NULL ; ) {
				STRTODEST(p);
				if (*ap)
					STPUTC('\0', expdest);
			}
			break;
		}
		/* fall through */
	case '*':
		if (ifsset() != 0)
			sep = ifsval()[0];
		else
			sep = ' ';
		for (ap = shellparam.p ; (p = *ap++) != NULL ; ) {
			STRTODEST(p);
			if (*ap && sep)
				STPUTC(sep, expdest);
		}
		break;
	case '0':
		p = arg0;
		STRTODEST(p);
		break;
	default:
		if (is_digit(*name)) {
			num = atoi(name);
			if (num > 0 && num <= shellparam.nparam) {
				p = shellparam.p[num - 1];
				STRTODEST(p);
			}
		}
		break;
	}
}



/*
 * Record the fact that we have to scan this region of the
 * string for IFS characters.
 */

STATIC void
recordregion(int start, int end, int inquotes)
{
	struct ifsregion *ifsp;

	if (ifslastp == NULL) {
		ifsp = &ifsfirst;
	} else {
		if (ifslastp->endoff == start
		    && ifslastp->inquotes == inquotes) {
			/* extend previous area */
			ifslastp->endoff = end;
			return;
		}
		ifsp = (struct ifsregion *)ckmalloc(sizeof (struct ifsregion));
		ifslastp->next = ifsp;
	}
	ifslastp = ifsp;
	ifslastp->next = NULL;
	ifslastp->begoff = start;
	ifslastp->endoff = end;
	ifslastp->inquotes = inquotes;
}



/*
 * Break the argument string into pieces based upon IFS and add the
 * strings to the argument list.  The regions of the string to be
 * searched for IFS characters have been stored by recordregion.
 */
STATIC void
ifsbreakup(char *string, struct arglist *arglist)
{
	struct ifsregion *ifsp;
	struct strlist *sp;
	char *start;
	char *p;
	char *q;
	const char *ifs;
	const char *ifsspc;
	int inquotes;

	start = string;
	ifsspc = NULL;
	inquotes = 0;

	if (ifslastp == NULL) {
		/* Return entire argument, IFS doesn't apply to any of it */
		sp = (struct strlist *)stalloc(sizeof *sp);
		sp->text = start;
		*arglist->lastp = sp;
		arglist->lastp = &sp->next;
		return;
	}

	ifs = ifsset() ? ifsval() : " \t\n";

	for (ifsp = &ifsfirst; ifsp != NULL; ifsp = ifsp->next) {
		p = string + ifsp->begoff;
		inquotes = ifsp->inquotes;
		ifsspc = NULL;
		while (p < string + ifsp->endoff) {
			q = p;
			if (*p == CTLESC)
				p++;
			if (inquotes) {
				/* Only NULs (probably from "$@") end args */
				if (*p != 0) {
					p++;
					continue;
				}
			} else {
				if (!strchr(ifs, *p)) {
					p++;
					continue;
				}
				ifsspc = strchr(" \t\n", *p);

				/* Ignore IFS whitespace at start */
				if (q == start && ifsspc != NULL) {
					p++;
					start = p;
					continue;
				}
			}

			/* Save this argument... */
			*q = '\0';
			sp = (struct strlist *)stalloc(sizeof *sp);
			sp->text = start;
			*arglist->lastp = sp;
			arglist->lastp = &sp->next;
			p++;

			if (ifsspc != NULL) {
				/* Ignore further trailing IFS whitespace */
				for (; p < string + ifsp->endoff; p++) {
					q = p;
					if (*p == CTLESC)
						p++;
					if (strchr(ifs, *p) == NULL) {
						p = q;
						break;
					}
					if (strchr(" \t\n", *p) == NULL) {
						p++;
						break;
					}
				}
			}
			start = p;
		}
	}

	/*
	 * Save anything left as an argument.
	 * Traditionally we have treated 'IFS=':'; set -- x$IFS' as
	 * generating 2 arguments, the second of which is empty.
	 * Some recent clarification of the Posix spec say that it
	 * should only generate one....
	 */
	if (*start /* || (!ifsspc && start > string) */) {
		sp = (struct strlist *)stalloc(sizeof *sp);
		sp->text = start;
		*arglist->lastp = sp;
		arglist->lastp = &sp->next;
	}
}