decode.c revision 195941 
1/*
2 * Copyright (C) 1984-2009  Mark Nudelman
3 *
4 * You may distribute under the terms of either the GNU General Public
5 * License or the Less License, as specified in the README file.
6 *
7 * For more information about less, or for information on how to
8 * contact the author, see the README file.
9 */
10
11
12/*
13 * Routines to decode user commands.
14 *
15 * This is all table driven.
16 * A command table is a sequence of command descriptors.
17 * Each command descriptor is a sequence of bytes with the following format:
18 *	<c1><c2>...<cN><0><action>
19 * The characters c1,c2,...,cN are the command string; that is,
20 * the characters which the user must type.
21 * It is terminated by a null <0> byte.
22 * The byte after the null byte is the action code associated
23 * with the command string.
24 * If an action byte is OR-ed with A_EXTRA, this indicates
25 * that the option byte is followed by an extra string.
26 *
27 * There may be many command tables.
28 * The first (default) table is built-in.
29 * Other tables are read in from "lesskey" files.
30 * All the tables are linked together and are searched in order.
31 */
32
33#include "less.h"
34#include "cmd.h"
35#include "lesskey.h"
36
37extern int erase_char, erase2_char, kill_char;
38extern int secure;
39
40#define SK(k) \
41	SK_SPECIAL_KEY, (k), 6, 1, 1, 1
42/*
43 * Command table is ordered roughly according to expected
44 * frequency of use, so the common commands are near the beginning.
45 */
46
47static unsigned char cmdtable[] =
48{
49	'\r',0,				A_F_LINE,
50	'\n',0,				A_F_LINE,
51	'e',0,				A_F_LINE,
52	'j',0,				A_F_LINE,
53	SK(SK_DOWN_ARROW),0,		A_F_LINE,
54	CONTROL('E'),0,			A_F_LINE,
55	CONTROL('N'),0,			A_F_LINE,
56	'k',0,				A_B_LINE,
57	'y',0,				A_B_LINE,
58	CONTROL('Y'),0,			A_B_LINE,
59	SK(SK_CONTROL_K),0,		A_B_LINE,
60	CONTROL('P'),0,			A_B_LINE,
61	SK(SK_UP_ARROW),0,		A_B_LINE,
62	'J',0,				A_FF_LINE,
63	'K',0,				A_BF_LINE,
64	'Y',0,				A_BF_LINE,
65	'd',0,				A_F_SCROLL,
66	CONTROL('D'),0,			A_F_SCROLL,
67	'u',0,				A_B_SCROLL,
68	CONTROL('U'),0,			A_B_SCROLL,
69	' ',0,				A_F_SCREEN,
70	'f',0,				A_F_SCREEN,
71	CONTROL('F'),0,			A_F_SCREEN,
72	CONTROL('V'),0,			A_F_SCREEN,
73	SK(SK_PAGE_DOWN),0,		A_F_SCREEN,
74	'b',0,				A_B_SCREEN,
75	CONTROL('B'),0,			A_B_SCREEN,
76	ESC,'v',0,			A_B_SCREEN,
77	SK(SK_PAGE_UP),0,		A_B_SCREEN,
78	'z',0,				A_F_WINDOW,
79	'w',0,				A_B_WINDOW,
80	ESC,' ',0,			A_FF_SCREEN,
81	'F',0,				A_F_FOREVER,
82	'R',0,				A_FREPAINT,
83	'r',0,				A_REPAINT,
84	CONTROL('R'),0,			A_REPAINT,
85	CONTROL('L'),0,			A_REPAINT,
86	ESC,'u',0,			A_UNDO_SEARCH,
87	'g',0,				A_GOLINE,
88	SK(SK_HOME),0,			A_GOLINE,
89	'<',0,				A_GOLINE,
90	ESC,'<',0,			A_GOLINE,
91	'p',0,				A_PERCENT,
92	'%',0,				A_PERCENT,
93	ESC,'[',0,			A_LSHIFT,
94	ESC,']',0,			A_RSHIFT,
95	ESC,'(',0,			A_LSHIFT,
96	ESC,')',0,			A_RSHIFT,
97	SK(SK_RIGHT_ARROW),0,		A_RSHIFT,
98	SK(SK_LEFT_ARROW),0,		A_LSHIFT,
99	'{',0,				A_F_BRACKET|A_EXTRA,	'{','}',0,
100	'}',0,				A_B_BRACKET|A_EXTRA,	'{','}',0,
101	'(',0,				A_F_BRACKET|A_EXTRA,	'(',')',0,
102	')',0,				A_B_BRACKET|A_EXTRA,	'(',')',0,
103	'[',0,				A_F_BRACKET|A_EXTRA,	'[',']',0,
104	']',0,				A_B_BRACKET|A_EXTRA,	'[',']',0,
105	ESC,CONTROL('F'),0,		A_F_BRACKET,
106	ESC,CONTROL('B'),0,		A_B_BRACKET,
107	'G',0,				A_GOEND,
108	ESC,'>',0,			A_GOEND,
109	'>',0,				A_GOEND,
110	SK(SK_END),0,			A_GOEND,
111	'P',0,				A_GOPOS,
112
113	'0',0,				A_DIGIT,
114	'1',0,				A_DIGIT,
115	'2',0,				A_DIGIT,
116	'3',0,				A_DIGIT,
117	'4',0,				A_DIGIT,
118	'5',0,				A_DIGIT,
119	'6',0,				A_DIGIT,
120	'7',0,				A_DIGIT,
121	'8',0,				A_DIGIT,
122	'9',0,				A_DIGIT,
123	'.',0,				A_DIGIT,
124
125	'=',0,				A_STAT,
126	CONTROL('G'),0,			A_STAT,
127	':','f',0,			A_STAT,
128	'/',0,				A_F_SEARCH,
129	'?',0,				A_B_SEARCH,
130	ESC,'/',0,			A_F_SEARCH|A_EXTRA,	'*',0,
131	ESC,'?',0,			A_B_SEARCH|A_EXTRA,	'*',0,
132	'n',0,				A_AGAIN_SEARCH,
133	ESC,'n',0,			A_T_AGAIN_SEARCH,
134	'N',0,				A_REVERSE_SEARCH,
135	ESC,'N',0,			A_T_REVERSE_SEARCH,
136	'&',0,				A_FILTER,
137	'm',0,				A_SETMARK,
138	'\'',0,				A_GOMARK,
139	CONTROL('X'),CONTROL('X'),0,	A_GOMARK,
140	'E',0,				A_EXAMINE,
141	':','e',0,			A_EXAMINE,
142	CONTROL('X'),CONTROL('V'),0,	A_EXAMINE,
143	':','n',0,			A_NEXT_FILE,
144	':','p',0,			A_PREV_FILE,
145	't',0,				A_NEXT_TAG,
146	'T',0,				A_PREV_TAG,
147	':','x',0,			A_INDEX_FILE,
148	':','d',0,			A_REMOVE_FILE,
149	'-',0,				A_OPT_TOGGLE,
150	':','t',0,			A_OPT_TOGGLE|A_EXTRA,	't',0,
151	's',0,				A_OPT_TOGGLE|A_EXTRA,	'o',0,
152	'_',0,				A_DISP_OPTION,
153	'|',0,				A_PIPE,
154	'v',0,				A_VISUAL,
155	'!',0,				A_SHELL,
156	'+',0,				A_FIRSTCMD,
157
158	'H',0,				A_HELP,
159	'h',0,				A_HELP,
160	SK(SK_F1),0,			A_HELP,
161	'V',0,				A_VERSION,
162	'q',0,				A_QUIT,
163	'Q',0,				A_QUIT,
164	':','q',0,			A_QUIT,
165	':','Q',0,			A_QUIT,
166	'Z','Z',0,			A_QUIT
167};
168
169static unsigned char edittable[] =
170{
171	'\t',0,	    			EC_F_COMPLETE,	/* TAB */
172	'\17',0,			EC_B_COMPLETE,	/* BACKTAB */
173	SK(SK_BACKTAB),0,		EC_B_COMPLETE,	/* BACKTAB */
174	ESC,'\t',0,			EC_B_COMPLETE,	/* ESC TAB */
175	CONTROL('L'),0,			EC_EXPAND,	/* CTRL-L */
176	CONTROL('V'),0,			EC_LITERAL,	/* BACKSLASH */
177	CONTROL('A'),0,			EC_LITERAL,	/* BACKSLASH */
178   	ESC,'l',0,			EC_RIGHT,	/* ESC l */
179	SK(SK_RIGHT_ARROW),0,		EC_RIGHT,	/* RIGHTARROW */
180	ESC,'h',0,			EC_LEFT,	/* ESC h */
181	SK(SK_LEFT_ARROW),0,		EC_LEFT,	/* LEFTARROW */
182	ESC,'b',0,			EC_W_LEFT,	/* ESC b */
183	ESC,SK(SK_LEFT_ARROW),0,	EC_W_LEFT,	/* ESC LEFTARROW */
184	SK(SK_CTL_LEFT_ARROW),0,	EC_W_LEFT,	/* CTRL-LEFTARROW */
185	ESC,'w',0,			EC_W_RIGHT,	/* ESC w */
186	ESC,SK(SK_RIGHT_ARROW),0,	EC_W_RIGHT,	/* ESC RIGHTARROW */
187	SK(SK_CTL_RIGHT_ARROW),0,	EC_W_RIGHT,	/* CTRL-RIGHTARROW */
188	ESC,'i',0,			EC_INSERT,	/* ESC i */
189	SK(SK_INSERT),0,		EC_INSERT,	/* INSERT */
190	ESC,'x',0,			EC_DELETE,	/* ESC x */
191	SK(SK_DELETE),0,		EC_DELETE,	/* DELETE */
192	ESC,'X',0,			EC_W_DELETE,	/* ESC X */
193	ESC,SK(SK_DELETE),0,		EC_W_DELETE,	/* ESC DELETE */
194	SK(SK_CTL_DELETE),0,		EC_W_DELETE,	/* CTRL-DELETE */
195	SK(SK_CTL_BACKSPACE),0,		EC_W_BACKSPACE, /* CTRL-BACKSPACE */
196	ESC,'\b',0,			EC_W_BACKSPACE,	/* ESC BACKSPACE */
197	ESC,'0',0,			EC_HOME,	/* ESC 0 */
198	SK(SK_HOME),0,			EC_HOME,	/* HOME */
199	ESC,'$',0,			EC_END,		/* ESC $ */
200	SK(SK_END),0,			EC_END,		/* END */
201	ESC,'k',0,			EC_UP,		/* ESC k */
202	SK(SK_UP_ARROW),0,		EC_UP,		/* UPARROW */
203	ESC,'j',0,			EC_DOWN,	/* ESC j */
204	SK(SK_DOWN_ARROW),0,		EC_DOWN,	/* DOWNARROW */
205};
206
207/*
208 * Structure to support a list of command tables.
209 */
210struct tablelist
211{
212	struct tablelist *t_next;
213	char *t_start;
214	char *t_end;
215};
216
217/*
218 * List of command tables and list of line-edit tables.
219 */
220static struct tablelist *list_fcmd_tables = NULL;
221static struct tablelist *list_ecmd_tables = NULL;
222static struct tablelist *list_var_tables = NULL;
223static struct tablelist *list_sysvar_tables = NULL;
224
225
226/*
227 * Expand special key abbreviations in a command table.
228 */
229	static void
230expand_special_keys(table, len)
231	char *table;
232	int len;
233{
234	register char *fm;
235	register char *to;
236	register int a;
237	char *repl;
238	int klen;
239
240	for (fm = table;  fm < table + len; )
241	{
242		/*
243		 * Rewrite each command in the table with any
244		 * special key abbreviations expanded.
245		 */
246		for (to = fm;  *fm != '\0'; )
247		{
248			if (*fm != SK_SPECIAL_KEY)
249			{
250				*to++ = *fm++;
251				continue;
252			}
253			/*
254			 * After SK_SPECIAL_KEY, next byte is the type
255			 * of special key (one of the SK_* contants),
256			 * and the byte after that is the number of bytes,
257			 * N, reserved by the abbreviation (including the
258			 * SK_SPECIAL_KEY and key type bytes).
259			 * Replace all N bytes with the actual bytes
260			 * output by the special key on this terminal.
261			 */
262			repl = special_key_str(fm[1]);
263			klen = fm[2] & 0377;
264			fm += klen;
265			if (repl == NULL || (int) strlen(repl) > klen)
266				repl = "\377";
267			while (*repl != '\0')
268				*to++ = *repl++;
269		}
270		*to++ = '\0';
271		/*
272		 * Fill any unused bytes between end of command and
273		 * the action byte with A_SKIP.
274		 */
275		while (to <= fm)
276			*to++ = A_SKIP;
277		fm++;
278		a = *fm++ & 0377;
279		if (a & A_EXTRA)
280		{
281			while (*fm++ != '\0')
282				continue;
283		}
284	}
285}
286
287/*
288 * Initialize the command lists.
289 */
290	public void
291init_cmds()
292{
293	/*
294	 * Add the default command tables.
295	 */
296	add_fcmd_table((char*)cmdtable, sizeof(cmdtable));
297	add_ecmd_table((char*)edittable, sizeof(edittable));
298#if USERFILE
299	/*
300	 * For backwards compatibility,
301	 * try to add tables in the OLD system lesskey file.
302	 */
303#ifdef BINDIR
304	add_hometable(NULL, BINDIR "/.sysless", 1);
305#endif
306	/*
307	 * Try to add the tables in the system lesskey file.
308	 */
309	add_hometable("LESSKEY_SYSTEM", LESSKEYFILE_SYS, 1);
310	/*
311	 * Try to add the tables in the standard lesskey file "$HOME/.less".
312	 */
313	add_hometable("LESSKEY", LESSKEYFILE, 0);
314#endif
315}
316
317/*
318 * Add a command table.
319 */
320	static int
321add_cmd_table(tlist, buf, len)
322	struct tablelist **tlist;
323	char *buf;
324	int len;
325{
326	register struct tablelist *t;
327
328	if (len == 0)
329		return (0);
330	/*
331	 * Allocate a tablelist structure, initialize it,
332	 * and link it into the list of tables.
333	 */
334	if ((t = (struct tablelist *)
335			calloc(1, sizeof(struct tablelist))) == NULL)
336	{
337		return (-1);
338	}
339	expand_special_keys(buf, len);
340	t->t_start = buf;
341	t->t_end = buf + len;
342	t->t_next = *tlist;
343	*tlist = t;
344	return (0);
345}
346
347/*
348 * Add a command table.
349 */
350	public void
351add_fcmd_table(buf, len)
352	char *buf;
353	int len;
354{
355	if (add_cmd_table(&list_fcmd_tables, buf, len) < 0)
356		error("Warning: some commands disabled", NULL_PARG);
357}
358
359/*
360 * Add an editing command table.
361 */
362	public void
363add_ecmd_table(buf, len)
364	char *buf;
365	int len;
366{
367	if (add_cmd_table(&list_ecmd_tables, buf, len) < 0)
368		error("Warning: some edit commands disabled", NULL_PARG);
369}
370
371/*
372 * Add an environment variable table.
373 */
374	static void
375add_var_table(tlist, buf, len)
376	struct tablelist **tlist;
377	char *buf;
378	int len;
379{
380	if (add_cmd_table(tlist, buf, len) < 0)
381		error("Warning: environment variables from lesskey file unavailable", NULL_PARG);
382}
383
384/*
385 * Search a single command table for the command string in cmd.
386 */
387	static int
388cmd_search(cmd, table, endtable, sp)
389	char *cmd;
390	char *table;
391	char *endtable;
392	char **sp;
393{
394	register char *p;
395	register char *q;
396	register int a;
397
398	*sp = NULL;
399	for (p = table, q = cmd;  p < endtable;  p++, q++)
400	{
401		if (*p == *q)
402		{
403			/*
404			 * Current characters match.
405			 * If we're at the end of the string, we've found it.
406			 * Return the action code, which is the character
407			 * after the null at the end of the string
408			 * in the command table.
409			 */
410			if (*p == '\0')
411			{
412				a = *++p & 0377;
413				while (a == A_SKIP)
414					a = *++p & 0377;
415				if (a == A_END_LIST)
416				{
417					/*
418					 * We get here only if the original
419					 * cmd string passed in was empty ("").
420					 * I don't think that can happen,
421					 * but just in case ...
422					 */
423					return (A_UINVALID);
424				}
425				/*
426				 * Check for an "extra" string.
427				 */
428				if (a & A_EXTRA)
429				{
430					*sp = ++p;
431					a &= ~A_EXTRA;
432				}
433				return (a);
434			}
435		} else if (*q == '\0')
436		{
437			/*
438			 * Hit the end of the user's command,
439			 * but not the end of the string in the command table.
440			 * The user's command is incomplete.
441			 */
442			return (A_PREFIX);
443		} else
444		{
445			/*
446			 * Not a match.
447			 * Skip ahead to the next command in the
448			 * command table, and reset the pointer
449			 * to the beginning of the user's command.
450			 */
451			if (*p == '\0' && p[1] == A_END_LIST)
452			{
453				/*
454				 * A_END_LIST is a special marker that tells
455				 * us to abort the cmd search.
456				 */
457				return (A_UINVALID);
458			}
459			while (*p++ != '\0')
460				continue;
461			while (*p == A_SKIP)
462				p++;
463			if (*p & A_EXTRA)
464				while (*++p != '\0')
465					continue;
466			q = cmd-1;
467		}
468	}
469	/*
470	 * No match found in the entire command table.
471	 */
472	return (A_INVALID);
473}
474
475/*
476 * Decode a command character and return the associated action.
477 * The "extra" string, if any, is returned in sp.
478 */
479	static int
480cmd_decode(tlist, cmd, sp)
481	struct tablelist *tlist;
482	char *cmd;
483	char **sp;
484{
485	register struct tablelist *t;
486	register int action = A_INVALID;
487
488	/*
489	 * Search thru all the command tables.
490	 * Stop when we find an action which is not A_INVALID.
491	 */
492	for (t = tlist;  t != NULL;  t = t->t_next)
493	{
494		action = cmd_search(cmd, t->t_start, t->t_end, sp);
495		if (action != A_INVALID)
496			break;
497	}
498	if (action == A_UINVALID)
499		action = A_INVALID;
500	return (action);
501}
502
503/*
504 * Decode a command from the cmdtables list.
505 */
506	public int
507fcmd_decode(cmd, sp)
508	char *cmd;
509	char **sp;
510{
511	return (cmd_decode(list_fcmd_tables, cmd, sp));
512}
513
514/*
515 * Decode a command from the edittables list.
516 */
517	public int
518ecmd_decode(cmd, sp)
519	char *cmd;
520	char **sp;
521{
522	return (cmd_decode(list_ecmd_tables, cmd, sp));
523}
524
525/*
526 * Get the value of an environment variable.
527 * Looks first in the lesskey file, then in the real environment.
528 */
529	public char *
530lgetenv(var)
531	char *var;
532{
533	int a;
534	char *s;
535
536	a = cmd_decode(list_var_tables, var, &s);
537	if (a == EV_OK)
538		return (s);
539	s = getenv(var);
540	if (s != NULL && *s != '\0')
541		return (s);
542	a = cmd_decode(list_sysvar_tables, var, &s);
543	if (a == EV_OK)
544		return (s);
545	return (NULL);
546}
547
548#if USERFILE
549/*
550 * Get an "integer" from a lesskey file.
551 * Integers are stored in a funny format:
552 * two bytes, low order first, in radix KRADIX.
553 */
554	static int
555gint(sp)
556	char **sp;
557{
558	int n;
559
560	n = *(*sp)++;
561	n += *(*sp)++ * KRADIX;
562	return (n);
563}
564
565/*
566 * Process an old (pre-v241) lesskey file.
567 */
568	static int
569old_lesskey(buf, len)
570	char *buf;
571	int len;
572{
573	/*
574	 * Old-style lesskey file.
575	 * The file must end with either
576	 *     ...,cmd,0,action
577	 * or  ...,cmd,0,action|A_EXTRA,string,0
578	 * So the last byte or the second to last byte must be zero.
579	 */
580	if (buf[len-1] != '\0' && buf[len-2] != '\0')
581		return (-1);
582	add_fcmd_table(buf, len);
583	return (0);
584}
585
586/*
587 * Process a new (post-v241) lesskey file.
588 */
589	static int
590new_lesskey(buf, len, sysvar)
591	char *buf;
592	int len;
593	int sysvar;
594{
595	char *p;
596	register int c;
597	register int n;
598
599	/*
600	 * New-style lesskey file.
601	 * Extract the pieces.
602	 */
603	if (buf[len-3] != C0_END_LESSKEY_MAGIC ||
604	    buf[len-2] != C1_END_LESSKEY_MAGIC ||
605	    buf[len-1] != C2_END_LESSKEY_MAGIC)
606		return (-1);
607	p = buf + 4;
608	for (;;)
609	{
610		c = *p++;
611		switch (c)
612		{
613		case CMD_SECTION:
614			n = gint(&p);
615			add_fcmd_table(p, n);
616			p += n;
617			break;
618		case EDIT_SECTION:
619			n = gint(&p);
620			add_ecmd_table(p, n);
621			p += n;
622			break;
623		case VAR_SECTION:
624			n = gint(&p);
625			add_var_table((sysvar) ?
626				&list_sysvar_tables : &list_var_tables, p, n);
627			p += n;
628			break;
629		case END_SECTION:
630			return (0);
631		default:
632			/*
633			 * Unrecognized section type.
634			 */
635			return (-1);
636		}
637	}
638}
639
640/*
641 * Set up a user command table, based on a "lesskey" file.
642 */
643	public int
644lesskey(filename, sysvar)
645	char *filename;
646	int sysvar;
647{
648	register char *buf;
649	register POSITION len;
650	register long n;
651	register int f;
652
653	if (secure)
654		return (1);
655	/*
656	 * Try to open the lesskey file.
657	 */
658	filename = shell_unquote(filename);
659	f = open(filename, OPEN_READ);
660	free(filename);
661	if (f < 0)
662		return (1);
663
664	/*
665	 * Read the file into a buffer.
666	 * We first figure out the size of the file and allocate space for it.
667	 * {{ Minimal error checking is done here.
668	 *    A garbage .less file will produce strange results.
669	 *    To avoid a large amount of error checking code here, we
670	 *    rely on the lesskey program to generate a good .less file. }}
671	 */
672	len = filesize(f);
673	if (len == NULL_POSITION || len < 3)
674	{
675		/*
676		 * Bad file (valid file must have at least 3 chars).
677		 */
678		close(f);
679		return (-1);
680	}
681	if ((buf = (char *) calloc((int)len, sizeof(char))) == NULL)
682	{
683		close(f);
684		return (-1);
685	}
686	if (lseek(f, (off_t)0, SEEK_SET) == BAD_LSEEK)
687	{
688		free(buf);
689		close(f);
690		return (-1);
691	}
692	n = read(f, buf, (unsigned int) len);
693	close(f);
694	if (n != len)
695	{
696		free(buf);
697		return (-1);
698	}
699
700	/*
701	 * Figure out if this is an old-style (before version 241)
702	 * or new-style lesskey file format.
703	 */
704	if (buf[0] != C0_LESSKEY_MAGIC || buf[1] != C1_LESSKEY_MAGIC ||
705	    buf[2] != C2_LESSKEY_MAGIC || buf[3] != C3_LESSKEY_MAGIC)
706		return (old_lesskey(buf, (int)len));
707	return (new_lesskey(buf, (int)len, sysvar));
708}
709
710/*
711 * Add the standard lesskey file "$HOME/.less"
712 */
713	public void
714add_hometable(envname, def_filename, sysvar)
715	char *envname;
716	char *def_filename;
717	int sysvar;
718{
719	char *filename;
720	PARG parg;
721
722	if (envname != NULL && (filename = lgetenv(envname)) != NULL)
723		filename = save(filename);
724	else if (sysvar)
725		filename = save(def_filename);
726	else
727		filename = homefile(def_filename);
728	if (filename == NULL)
729		return;
730	if (lesskey(filename, sysvar) < 0)
731	{
732		parg.p_string = filename;
733		error("Cannot use lesskey file \"%s\"", &parg);
734	}
735	free(filename);
736}
737#endif
738
739/*
740 * See if a char is a special line-editing command.
741 */
742	public int
743editchar(c, flags)
744	int c;
745	int flags;
746{
747	int action;
748	int nch;
749	char *s;
750	char usercmd[MAX_CMDLEN+1];
751
752	/*
753	 * An editing character could actually be a sequence of characters;
754	 * for example, an escape sequence sent by pressing the uparrow key.
755	 * To match the editing string, we use the command decoder
756	 * but give it the edit-commands command table
757	 * This table is constructed to match the user's keyboard.
758	 */
759	if (c == erase_char || c == erase2_char)
760		return (EC_BACKSPACE);
761	if (c == kill_char)
762		return (EC_LINEKILL);
763
764	/*
765	 * Collect characters in a buffer.
766	 * Start with the one we have, and get more if we need them.
767	 */
768	nch = 0;
769	do {
770	  	if (nch > 0)
771			c = getcc();
772		usercmd[nch] = c;
773		usercmd[nch+1] = '\0';
774		nch++;
775		action = ecmd_decode(usercmd, &s);
776	} while (action == A_PREFIX);
777
778	if (flags & EC_NORIGHTLEFT)
779	{
780		switch (action)
781		{
782		case EC_RIGHT:
783		case EC_LEFT:
784			action = A_INVALID;
785			break;
786		}
787	}
788#if CMD_HISTORY
789	if (flags & EC_NOHISTORY)
790	{
791		/*
792		 * The caller says there is no history list.
793		 * Reject any history-manipulation action.
794		 */
795		switch (action)
796		{
797		case EC_UP:
798		case EC_DOWN:
799			action = A_INVALID;
800			break;
801		}
802	}
803#endif
804#if TAB_COMPLETE_FILENAME
805	if (flags & EC_NOCOMPLETE)
806	{
807		/*
808		 * The caller says we don't want any filename completion cmds.
809		 * Reject them.
810		 */
811		switch (action)
812		{
813		case EC_F_COMPLETE:
814		case EC_B_COMPLETE:
815		case EC_EXPAND:
816			action = A_INVALID;
817			break;
818		}
819	}
820#endif
821	if ((flags & EC_PEEK) || action == A_INVALID)
822	{
823		/*
824		 * We're just peeking, or we didn't understand the command.
825		 * Unget all the characters we read in the loop above.
826		 * This does NOT include the original character that was
827		 * passed in as a parameter.
828		 */
829		while (nch > 1)
830		{
831			ungetcc(usercmd[--nch]);
832		}
833	} else
834	{
835		if (s != NULL)
836			ungetsc(s);
837	}
838	return action;
839}
840
841