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IABSD.fr/src/bin/ksh/syn.c

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  • Author : millert
    Date : 2021-07-05 13:41:46
    Hash : 4685f242
    Message : Do not permit an empty list between "while" and "do". This avoids a cpu loop for "while do done" and is consistent with the behavior of AT&T ksh and most other shells. OK jca@ halex@

  • bin/ksh/syn.c
  • /*	$OpenBSD: syn.c,v 1.40 2021/07/05 13:41:46 millert Exp $	*/
    
    /*
     * shell parser (C version)
     */
    
    #include <string.h>
    
    #include "sh.h"
    #include "c_test.h"
    
    struct nesting_state {
    	int	start_token;	/* token than began nesting (eg, FOR) */
    	int	start_line;	/* line nesting began on */
    };
    
    static void	yyparse(void);
    static struct op *pipeline(int);
    static struct op *andor(void);
    static struct op *c_list(int);
    static struct ioword *synio(int);
    static void	musthave(int, int);
    static struct op *nested(int, int, int);
    static struct op *get_command(int);
    static struct op *dogroup(void);
    static struct op *thenpart(void);
    static struct op *elsepart(void);
    static struct op *caselist(void);
    static struct op *casepart(int);
    static struct op *function_body(char *, int);
    static char **	wordlist(void);
    static struct op *block(int, struct op *, struct op *, char **);
    static struct op *newtp(int);
    static void	syntaxerr(const char *) __attribute__((__noreturn__));
    static void	nesting_push(struct nesting_state *, int);
    static void	nesting_pop(struct nesting_state *);
    static int	assign_command(char *);
    static int	inalias(struct source *);
    static int	dbtestp_isa(Test_env *, Test_meta);
    static const char *dbtestp_getopnd(Test_env *, Test_op, int);
    static int	dbtestp_eval(Test_env *, Test_op, const char *, const char *,
    		    int);
    static void	dbtestp_error(Test_env *, int, const char *);
    
    static	struct	op	*outtree; /* yyparse output */
    
    static struct nesting_state nesting;	/* \n changed to ; */
    
    static	int	reject;		/* token(cf) gets symbol again */
    static	int	symbol;		/* yylex value */
    
    #define	token(cf) \
    	((reject) ? (reject = false, symbol) : (symbol = yylex(cf)))
    #define	tpeek(cf) \
    	((reject) ? (symbol) : (reject = true, symbol = yylex(cf)))
    
    static void
    yyparse(void)
    {
    	int c;
    
    	reject = false;
    
    	outtree = c_list(source->type == SSTRING);
    	c = tpeek(0);
    	if (c == 0 && !outtree)
    		outtree = newtp(TEOF);
    	else if (c != '\n' && c != 0)
    		syntaxerr(NULL);
    }
    
    static struct op *
    pipeline(int cf)
    {
    	struct op *t, *p, *tl = NULL;
    
    	t = get_command(cf);
    	if (t != NULL) {
    		while (token(0) == '|') {
    			if ((p = get_command(CONTIN)) == NULL)
    				syntaxerr(NULL);
    			if (tl == NULL)
    				t = tl = block(TPIPE, t, p, NULL);
    			else
    				tl = tl->right = block(TPIPE, tl->right, p, NULL);
    		}
    		reject = true;
    	}
    	return (t);
    }
    
    static struct op *
    andor(void)
    {
    	struct op *t, *p;
    	int c;
    
    	t = pipeline(0);
    	if (t != NULL) {
    		while ((c = token(0)) == LOGAND || c == LOGOR) {
    			if ((p = pipeline(CONTIN)) == NULL)
    				syntaxerr(NULL);
    			t = block(c == LOGAND? TAND: TOR, t, p, NULL);
    		}
    		reject = true;
    	}
    	return (t);
    }
    
    static struct op *
    c_list(int multi)
    {
    	struct op *t = NULL, *p, *tl = NULL;
    	int c;
    	int have_sep;
    
    	while (1) {
    		p = andor();
    		/* Token has always been read/rejected at this point, so
    		 * we don't worry about what flags to pass token()
    		 */
    		c = token(0);
    		have_sep = 1;
    		if (c == '\n' && (multi || inalias(source))) {
    			if (!p) /* ignore blank lines */
    				continue;
    		} else if (!p)
    			break;
    		else if (c == '&' || c == COPROC)
    			p = block(c == '&' ? TASYNC : TCOPROC,
    				  p, NULL, NULL);
    		else if (c != ';')
    			have_sep = 0;
    		if (!t)
    			t = p;
    		else if (!tl)
    			t = tl = block(TLIST, t, p, NULL);
    		else
    			tl = tl->right = block(TLIST, tl->right, p, NULL);
    		if (!have_sep)
    			break;
    	}
    	reject = true;
    	return t;
    }
    
    static struct ioword *
    synio(int cf)
    {
    	struct ioword *iop;
    	int ishere;
    
    	if (tpeek(cf) != REDIR)
    		return NULL;
    	reject = false;
    	iop = yylval.iop;
    	ishere = (iop->flag&IOTYPE) == IOHERE;
    	musthave(LWORD, ishere ? HEREDELIM : 0);
    	if (ishere) {
    		iop->delim = yylval.cp;
    		if (*ident != 0) /* unquoted */
    			iop->flag |= IOEVAL;
    		if (herep >= &heres[HERES])
    			yyerror("too many <<'s\n");
    		*herep++ = iop;
    	} else
    		iop->name = yylval.cp;
    	return iop;
    }
    
    static void
    musthave(int c, int cf)
    {
    	if ((token(cf)) != c)
    		syntaxerr(NULL);
    }
    
    static struct op *
    nested(int type, int smark, int emark)
    {
    	struct op *t;
    	struct nesting_state old_nesting;
    
    	nesting_push(&old_nesting, smark);
    	t = c_list(true);
    	musthave(emark, KEYWORD|ALIAS);
    	nesting_pop(&old_nesting);
    	return (block(type, t, NULL, NULL));
    }
    
    static struct op *
    get_command(int cf)
    {
    	struct op *t;
    	int c, iopn = 0, syniocf;
    	struct ioword *iop, **iops;
    	XPtrV args, vars;
    	struct nesting_state old_nesting;
    
    	iops = areallocarray(NULL, NUFILE + 1,
    	    sizeof(struct ioword *), ATEMP);
    	XPinit(args, 16);
    	XPinit(vars, 16);
    
    	syniocf = KEYWORD|ALIAS;
    	switch (c = token(cf|KEYWORD|ALIAS|VARASN)) {
    	default:
    		reject = true;
    		afree(iops, ATEMP);
    		XPfree(args);
    		XPfree(vars);
    		return NULL; /* empty line */
    
    	case LWORD:
    	case REDIR:
    		reject = true;
    		syniocf &= ~(KEYWORD|ALIAS);
    		t = newtp(TCOM);
    		t->lineno = source->line;
    		while (1) {
    			cf = (t->u.evalflags ? ARRAYVAR : 0) |
    			    (XPsize(args) == 0 ? ALIAS|VARASN : CMDWORD);
    			switch (tpeek(cf)) {
    			case REDIR:
    				if (iopn >= NUFILE)
    					yyerror("too many redirections\n");
    				iops[iopn++] = synio(cf);
    				break;
    
    			case LWORD:
    				reject = false;
    				/* the iopn == 0 and XPsize(vars) == 0 are
    				 * dubious but at&t ksh acts this way
    				 */
    				if (iopn == 0 && XPsize(vars) == 0 &&
    				    XPsize(args) == 0 &&
    				    assign_command(ident))
    					t->u.evalflags = DOVACHECK;
    				if ((XPsize(args) == 0 || Flag(FKEYWORD)) &&
    				    is_wdvarassign(yylval.cp))
    					XPput(vars, yylval.cp);
    				else
    					XPput(args, yylval.cp);
    				break;
    
    			case '(':
    				/* Check for "> foo (echo hi)", which at&t ksh
    				 * allows (not POSIX, but not disallowed)
    				 */
    				afree(t, ATEMP);
    				if (XPsize(args) == 0 && XPsize(vars) == 0) {
    					reject = false;
    					goto Subshell;
    				}
    				/* Must be a function */
    				if (iopn != 0 || XPsize(args) != 1 ||
    				    XPsize(vars) != 0)
    					syntaxerr(NULL);
    				reject = false;
    				/*(*/
    				musthave(')', 0);
    				t = function_body(XPptrv(args)[0], false);
    				goto Leave;
    
    			default:
    				goto Leave;
    			}
    		}
    	  Leave:
    		break;
    
    	  Subshell:
    	case '(':
    		t = nested(TPAREN, '(', ')');
    		break;
    
    	case '{': /*}*/
    		t = nested(TBRACE, '{', '}');
    		break;
    
    	case MDPAREN:
    	  {
    		static const char let_cmd[] = {
    			CHAR, 'l', CHAR, 'e',
    			CHAR, 't', EOS
    		};
    		/* Leave KEYWORD in syniocf (allow if (( 1 )) then ...) */
    		t = newtp(TCOM);
    		t->lineno = source->line;
    		reject = false;
    		XPput(args, wdcopy(let_cmd, ATEMP));
    		musthave(LWORD,LETEXPR);
    		XPput(args, yylval.cp);
    		break;
    	  }
    
    	case DBRACKET: /* [[ .. ]] */
    		/* Leave KEYWORD in syniocf (allow if [[ -n 1 ]] then ...) */
    		t = newtp(TDBRACKET);
    		reject = false;
    		{
    			Test_env te;
    
    			te.flags = TEF_DBRACKET;
    			te.pos.av = &args;
    			te.isa = dbtestp_isa;
    			te.getopnd = dbtestp_getopnd;
    			te.eval = dbtestp_eval;
    			te.error = dbtestp_error;
    
    			test_parse(&te);
    		}
    		break;
    
    	case FOR:
    	case SELECT:
    		t = newtp((c == FOR) ? TFOR : TSELECT);
    		musthave(LWORD, ARRAYVAR);
    		if (!is_wdvarname(yylval.cp, true))
    			yyerror("%s: bad identifier\n",
    			    c == FOR ? "for" : "select");
    		t->str = str_save(ident, ATEMP);
    		nesting_push(&old_nesting, c);
    		t->vars = wordlist();
    		t->left = dogroup();
    		nesting_pop(&old_nesting);
    		break;
    
    	case WHILE:
    	case UNTIL:
    		nesting_push(&old_nesting, c);
    		t = newtp((c == WHILE) ? TWHILE : TUNTIL);
    		t->left = c_list(true);
    		if (t->left == NULL)
    			syntaxerr(NULL);
    		t->right = dogroup();
    		nesting_pop(&old_nesting);
    		break;
    
    	case CASE:
    		t = newtp(TCASE);
    		musthave(LWORD, 0);
    		t->str = yylval.cp;
    		nesting_push(&old_nesting, c);
    		t->left = caselist();
    		nesting_pop(&old_nesting);
    		break;
    
    	case IF:
    		nesting_push(&old_nesting, c);
    		t = newtp(TIF);
    		t->left = c_list(true);
    		t->right = thenpart();
    		musthave(FI, KEYWORD|ALIAS);
    		nesting_pop(&old_nesting);
    		break;
    
    	case BANG:
    		syniocf &= ~(KEYWORD|ALIAS);
    		t = pipeline(0);
    		if (t == NULL)
    			syntaxerr(NULL);
    		t = block(TBANG, NULL, t, NULL);
    		break;
    
    	case TIME:
    		syniocf &= ~(KEYWORD|ALIAS);
    		t = pipeline(0);
    		if (t) {
    			if (t->str) {
    				t->str = str_save(t->str, ATEMP);
    			} else {
    				t->str = alloc(2, ATEMP);
    				t->str[0] = '\0'; /* TF_* flags */
    				t->str[1] = '\0';
    			}
    		}
    		t = block(TTIME, t, NULL, NULL);
    		break;
    
    	case FUNCTION:
    		musthave(LWORD, 0);
    		t = function_body(yylval.cp, true);
    		break;
    	}
    
    	while ((iop = synio(syniocf)) != NULL) {
    		if (iopn >= NUFILE)
    			yyerror("too many redirections\n");
    		iops[iopn++] = iop;
    	}
    
    	if (iopn == 0) {
    		afree(iops, ATEMP);
    		t->ioact = NULL;
    	} else {
    		iops[iopn++] = NULL;
    		iops = areallocarray(iops, iopn,
    		    sizeof(struct ioword *), ATEMP);
    		t->ioact = iops;
    	}
    
    	if (t->type == TCOM || t->type == TDBRACKET) {
    		XPput(args, NULL);
    		t->args = (char **) XPclose(args);
    		XPput(vars, NULL);
    		t->vars = (char **) XPclose(vars);
    	} else {
    		XPfree(args);
    		XPfree(vars);
    	}
    
    	return t;
    }
    
    static struct op *
    dogroup(void)
    {
    	int c;
    	struct op *list;
    
    	c = token(CONTIN|KEYWORD|ALIAS);
    	/* A {...} can be used instead of do...done for for/select loops
    	 * but not for while/until loops - we don't need to check if it
    	 * is a while loop because it would have been parsed as part of
    	 * the conditional command list...
    	 */
    	if (c == DO)
    		c = DONE;
    	else if (c == '{')
    		c = '}';
    	else
    		syntaxerr(NULL);
    	list = c_list(true);
    	musthave(c, KEYWORD|ALIAS);
    	return list;
    }
    
    static struct op *
    thenpart(void)
    {
    	struct op *t;
    
    	musthave(THEN, KEYWORD|ALIAS);
    	t = newtp(0);
    	t->left = c_list(true);
    	if (t->left == NULL)
    		syntaxerr(NULL);
    	t->right = elsepart();
    	return (t);
    }
    
    static struct op *
    elsepart(void)
    {
    	struct op *t;
    
    	switch (token(KEYWORD|ALIAS|VARASN)) {
    	case ELSE:
    		if ((t = c_list(true)) == NULL)
    			syntaxerr(NULL);
    		return (t);
    
    	case ELIF:
    		t = newtp(TELIF);
    		t->left = c_list(true);
    		t->right = thenpart();
    		return (t);
    
    	default:
    		reject = true;
    	}
    	return NULL;
    }
    
    static struct op *
    caselist(void)
    {
    	struct op *t, *tl;
    	int c;
    
    	c = token(CONTIN|KEYWORD|ALIAS);
    	/* A {...} can be used instead of in...esac for case statements */
    	if (c == IN)
    		c = ESAC;
    	else if (c == '{')
    		c = '}';
    	else
    		syntaxerr(NULL);
    	t = tl = NULL;
    	while ((tpeek(CONTIN|KEYWORD|ESACONLY)) != c) { /* no ALIAS here */
    		struct op *tc = casepart(c);
    		if (tl == NULL)
    			t = tl = tc, tl->right = NULL;
    		else
    			tl->right = tc, tl = tc;
    	}
    	musthave(c, KEYWORD|ALIAS);
    	return (t);
    }
    
    static struct op *
    casepart(int endtok)
    {
    	struct op *t;
    	int c;
    	XPtrV ptns;
    
    	XPinit(ptns, 16);
    	t = newtp(TPAT);
    	c = token(CONTIN|KEYWORD); /* no ALIAS here */
    	if (c != '(')
    		reject = true;
    	do {
    		musthave(LWORD, 0);
    		XPput(ptns, yylval.cp);
    	} while ((c = token(0)) == '|');
    	reject = true;
    	XPput(ptns, NULL);
    	t->vars = (char **) XPclose(ptns);
    	musthave(')', 0);
    
    	t->left = c_list(true);
    	/* Note: Posix requires the ;; */
    	if ((tpeek(CONTIN|KEYWORD|ALIAS)) != endtok)
    		musthave(BREAK, CONTIN|KEYWORD|ALIAS);
    	return (t);
    }
    
    static struct op *
    function_body(char *name,
        int ksh_func)		/* function foo { ... } vs foo() { .. } */
    {
    	char *sname, *p;
    	struct op *t;
    	int old_func_parse;
    
    	sname = wdstrip(name);
    	/* Check for valid characters in name.  posix and ksh93 say only
    	 * allow [a-zA-Z_0-9] but this allows more as old pdksh's have
    	 * allowed more (the following were never allowed:
    	 *	nul space nl tab $ ' " \ ` ( ) & | ; = < >
    	 *  C_QUOTE covers all but = and adds # [ ? *)
    	 */
    	for (p = sname; *p; p++)
    		if (ctype(*p, C_QUOTE) || *p == '=')
    			yyerror("%s: invalid function name\n", sname);
    
    	t = newtp(TFUNCT);
    	t->str = sname;
    	t->u.ksh_func = ksh_func;
    	t->lineno = source->line;
    
    	/* Note that POSIX allows only compound statements after foo(), sh and
    	 * at&t ksh allow any command, go with the later since it shouldn't
    	 * break anything.  However, for function foo, at&t ksh only accepts
    	 * an open-brace.
    	 */
    	if (ksh_func) {
    		musthave('{', CONTIN|KEYWORD|ALIAS); /* } */
    		reject = true;
    	}
    
    	old_func_parse = genv->flags & EF_FUNC_PARSE;
    	genv->flags |= EF_FUNC_PARSE;
    	if ((t->left = get_command(CONTIN)) == NULL) {
    		/*
    		 * Probably something like foo() followed by eof or ;.
    		 * This is accepted by sh and ksh88.
    		 * To make "typeset -f foo" work reliably (so its output can
    		 * be used as input), we pretend there is a colon here.
    		 */
    		t->left = newtp(TCOM);
    		t->left->args = areallocarray(NULL, 2, sizeof(char *), ATEMP);
    		t->left->args[0] = alloc(3, ATEMP);
    		t->left->args[0][0] = CHAR;
    		t->left->args[0][1] = ':';
    		t->left->args[0][2] = EOS;
    		t->left->args[1] = NULL;
    		t->left->vars = alloc(sizeof(char *), ATEMP);
    		t->left->vars[0] = NULL;
    		t->left->lineno = 1;
    	}
    	if (!old_func_parse)
    		genv->flags &= ~EF_FUNC_PARSE;
    
    	return t;
    }
    
    static char **
    wordlist(void)
    {
    	int c;
    	XPtrV args;
    
    	XPinit(args, 16);
    	/* Posix does not do alias expansion here... */
    	if ((c = token(CONTIN|KEYWORD|ALIAS)) != IN) {
    		if (c != ';') /* non-POSIX, but at&t ksh accepts a ; here */
    			reject = true;
    		return NULL;
    	}
    	while ((c = token(0)) == LWORD)
    		XPput(args, yylval.cp);
    	if (c != '\n' && c != ';')
    		syntaxerr(NULL);
    	XPput(args, NULL);
    	return (char **) XPclose(args);
    }
    
    /*
     * supporting functions
     */
    
    static struct op *
    block(int type, struct op *t1, struct op *t2, char **wp)
    {
    	struct op *t;
    
    	t = newtp(type);
    	t->left = t1;
    	t->right = t2;
    	t->vars = wp;
    	return (t);
    }
    
    const	struct tokeninfo {
    	const char *name;
    	short	val;
    	short	reserved;
    } tokentab[] = {
    	/* Reserved words */
    	{ "if",		IF,	true },
    	{ "then",	THEN,	true },
    	{ "else",	ELSE,	true },
    	{ "elif",	ELIF,	true },
    	{ "fi",		FI,	true },
    	{ "case",	CASE,	true },
    	{ "esac",	ESAC,	true },
    	{ "for",	FOR,	true },
    	{ "select",	SELECT,	true },
    	{ "while",	WHILE,	true },
    	{ "until",	UNTIL,	true },
    	{ "do",		DO,	true },
    	{ "done",	DONE,	true },
    	{ "in",		IN,	true },
    	{ "function",	FUNCTION, true },
    	{ "time",	TIME,	true },
    	{ "{",		'{',	true },
    	{ "}",		'}',	true },
    	{ "!",		BANG,	true },
    	{ "[[",		DBRACKET, true },
    	/* Lexical tokens (0[EOF], LWORD and REDIR handled specially) */
    	{ "&&",		LOGAND,	false },
    	{ "||",		LOGOR,	false },
    	{ ";;",		BREAK,	false },
    	{ "((",		MDPAREN, false },
    	{ "|&",		COPROC,	false },
    	/* and some special cases... */
    	{ "newline",	'\n',	false },
    	{ 0 }
    };
    
    void
    initkeywords(void)
    {
    	struct tokeninfo const *tt;
    	struct tbl *p;
    
    	ktinit(&keywords, APERM, 32); /* must be 2^n (currently 20 keywords) */
    	for (tt = tokentab; tt->name; tt++) {
    		if (tt->reserved) {
    			p = ktenter(&keywords, tt->name, hash(tt->name));
    			p->flag |= DEFINED|ISSET;
    			p->type = CKEYWD;
    			p->val.i = tt->val;
    		}
    	}
    }
    
    static void
    syntaxerr(const char *what)
    {
    	char redir[6];	/* 2<<- is the longest redirection, I think */
    	const char *s;
    	struct tokeninfo const *tt;
    	int c;
    
    	if (!what)
    		what = "unexpected";
    	reject = true;
    	c = token(0);
        Again:
    	switch (c) {
    	case 0:
    		if (nesting.start_token) {
    			c = nesting.start_token;
    			source->errline = nesting.start_line;
    			what = "unmatched";
    			goto Again;
    		}
    		/* don't quote the EOF */
    		yyerror("syntax error: unexpected EOF\n");
    		/* NOTREACHED */
    
    	case LWORD:
    		s = snptreef(NULL, 32, "%S", yylval.cp);
    		break;
    
    	case REDIR:
    		s = snptreef(redir, sizeof(redir), "%R", yylval.iop);
    		break;
    
    	default:
    		for (tt = tokentab; tt->name; tt++)
    			if (tt->val == c)
    			    break;
    		if (tt->name)
    			s = tt->name;
    		else {
    			if (c > 0 && c < 256) {
    				redir[0] = c;
    				redir[1] = '\0';
    			} else
    				shf_snprintf(redir, sizeof(redir),
    					"?%d", c);
    			s = redir;
    		}
    	}
    	yyerror("syntax error: `%s' %s\n", s, what);
    }
    
    static void
    nesting_push(struct nesting_state *save, int tok)
    {
    	*save = nesting;
    	nesting.start_token = tok;
    	nesting.start_line = source->line;
    }
    
    static void
    nesting_pop(struct nesting_state *saved)
    {
    	nesting = *saved;
    }
    
    static struct op *
    newtp(int type)
    {
    	struct op *t;
    
    	t = alloc(sizeof(*t), ATEMP);
    	t->type = type;
    	t->u.evalflags = 0;
    	t->args = t->vars = NULL;
    	t->ioact = NULL;
    	t->left = t->right = NULL;
    	t->str = NULL;
    	return (t);
    }
    
    struct op *
    compile(Source *s)
    {
    	nesting.start_token = 0;
    	nesting.start_line = 0;
    	herep = heres;
    	source = s;
    	yyparse();
    	return outtree;
    }
    
    /* This kludge exists to take care of sh/at&t ksh oddity in which
     * the arguments of alias/export/readonly/typeset have no field
     * splitting, file globbing, or (normal) tilde expansion done.
     * at&t ksh seems to do something similar to this since
     *	$ touch a=a; typeset a=[ab]; echo "$a"
     *	a=[ab]
     *	$ x=typeset; $x a=[ab]; echo "$a"
     *	a=a
     *	$
     */
    static int
    assign_command(char *s)
    {
    	if (Flag(FPOSIX) || !*s)
    		return 0;
    	return (strcmp(s, "alias") == 0) ||
    	    (strcmp(s, "export") == 0) ||
    	    (strcmp(s, "readonly") == 0) ||
    	    (strcmp(s, "typeset") == 0);
    }
    
    /* Check if we are in the middle of reading an alias */
    static int
    inalias(struct source *s)
    {
    	for (; s && s->type == SALIAS; s = s->next)
    		if (!(s->flags & SF_ALIASEND))
    			return 1;
    	return 0;
    }
    
    
    /* Order important - indexed by Test_meta values
     * Note that ||, &&, ( and ) can't appear in as unquoted strings
     * in normal shell input, so these can be interpreted unambiguously
     * in the evaluation pass.
     */
    static const char dbtest_or[] = { CHAR, '|', CHAR, '|', EOS };
    static const char dbtest_and[] = { CHAR, '&', CHAR, '&', EOS };
    static const char dbtest_not[] = { CHAR, '!', EOS };
    static const char dbtest_oparen[] = { CHAR, '(', EOS };
    static const char dbtest_cparen[] = { CHAR, ')', EOS };
    const char *const dbtest_tokens[] = {
    	dbtest_or, dbtest_and, dbtest_not,
    	dbtest_oparen, dbtest_cparen
    };
    const char db_close[] = { CHAR, ']', CHAR, ']', EOS };
    const char db_lthan[] = { CHAR, '<', EOS };
    const char db_gthan[] = { CHAR, '>', EOS };
    
    /* Test if the current token is a whatever.  Accepts the current token if
     * it is.  Returns 0 if it is not, non-zero if it is (in the case of
     * TM_UNOP and TM_BINOP, the returned value is a Test_op).
     */
    static int
    dbtestp_isa(Test_env *te, Test_meta meta)
    {
    	int c = tpeek(ARRAYVAR | (meta == TM_BINOP ? 0 : CONTIN));
    	int uqword = 0;
    	char *save = NULL;
    	int ret = 0;
    
    	/* unquoted word? */
    	uqword = c == LWORD && *ident;
    
    	if (meta == TM_OR)
    		ret = c == LOGOR;
    	else if (meta == TM_AND)
    		ret = c == LOGAND;
    	else if (meta == TM_NOT)
    		ret = uqword && strcmp(yylval.cp, dbtest_tokens[(int) TM_NOT]) == 0;
    	else if (meta == TM_OPAREN)
    		ret = c == '(' /*)*/;
    	else if (meta == TM_CPAREN)
    		ret = c == /*(*/ ')';
    	else if (meta == TM_UNOP || meta == TM_BINOP) {
    		if (meta == TM_BINOP && c == REDIR &&
    		    (yylval.iop->flag == IOREAD || yylval.iop->flag == IOWRITE)) {
    			ret = 1;
    			save = wdcopy(yylval.iop->flag == IOREAD ?
    			    db_lthan : db_gthan, ATEMP);
    		} else if (uqword && (ret = (int) test_isop(te, meta, ident)))
    			save = yylval.cp;
    	} else /* meta == TM_END */
    		ret = uqword && strcmp(yylval.cp, db_close) == 0;
    	if (ret) {
    		reject = false;
    		if (meta != TM_END) {
    			if (!save)
    				save = wdcopy(dbtest_tokens[(int) meta], ATEMP);
    			XPput(*te->pos.av, save);
    		}
    	}
    	return ret;
    }
    
    static const char *
    dbtestp_getopnd(Test_env *te, Test_op op, int do_eval)
    {
    	int c = tpeek(ARRAYVAR);
    
    	if (c != LWORD)
    		return NULL;
    
    	reject = false;
    	XPput(*te->pos.av, yylval.cp);
    
    	return null;
    }
    
    static int
    dbtestp_eval(Test_env *te, Test_op op, const char *opnd1, const char *opnd2,
        int do_eval)
    {
    	return 1;
    }
    
    static void
    dbtestp_error(Test_env *te, int offset, const char *msg)
    {
    	te->flags |= TEF_ERROR;
    
    	if (offset < 0) {
    		reject = true;
    		/* Kludgy to say the least... */
    		symbol = LWORD;
    		yylval.cp = *(XPptrv(*te->pos.av) + XPsize(*te->pos.av) +
    		    offset);
    	}
    	syntaxerr(msg);
    }