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Delete support for the LESSOPEN and LESSCLOSE environment variables
aka the "Input Preprocessor": it's been a source for multiple
security bugs in the past as everything has to deal with handling
arbitrary filenames and generally resulted in multiple TOCTOU issues.
The base system never included a default LESSOPEN setting like some
Linux distributions did, but it's a suds-filled sink full of knives
to try to use safely.

ok tb@ deraadt@ millert@

/*
 * Copyright (C) 1984-2012  Mark Nudelman
 * Modified for use with illumos by Garrett D'Amore.
 * Copyright 2014 Garrett D'Amore <garrett@damore.org>
 *
 * You may distribute under the terms of either the GNU General Public
 * License or the Less License, as specified in the README file.
 *
 * For more information, see the README file.
 */

/*
 * User-level command processor.
 */

#include "cmd.h"
#include "less.h"
#include "option.h"
#include "position.h"

extern int erase_char, erase2_char, kill_char;
extern int quit_if_one_screen;
extern int less_is_more;
extern int squished;
extern int sc_width;
extern int sc_height;
extern int swindow;
extern int jump_sline;
extern int quitting;
extern int wscroll;
extern int top_scroll;
extern int ignore_eoi;
extern int secure;
extern int hshift;
extern int show_attn;
extern off_t highest_hilite;
extern char *every_first_cmd;
extern char version[];
extern struct scrpos initial_scrpos;
extern IFILE curr_ifile;
extern void *ml_search;
extern void *ml_examine;
extern void *ml_shell;
extern char *editor;
extern char *editproto;
extern int screen_trashed;	/* The screen has been overwritten */
extern int shift_count;
extern int oldbot;
extern int forw_prompt;

static int mca;			/* The multicharacter command (action) */
static int search_type;		/* The previous type of search */
static off_t number;		/* The number typed by the user */
static long fraction;		/* The fractional part of the number */
static struct loption *curropt;
static int opt_lower;
static int optflag;
static int optgetname;
static off_t bottompos;
static int save_hshift;
static int pipec;

struct ungot {
	struct ungot *ug_next;
	int ug_char;
};
static struct ungot *ungot = NULL;
static int unget_end = 0;

static void multi_search(char *, int);

/*
 * Move the cursor to start of prompt line before executing a command.
 * This looks nicer if the command takes a long time before
 * updating the screen.
 */
static void
cmd_exec(void)
{
	clear_attn();
	clear_bot();
	flush(0);
}

/*
 * Set up the display to start a new multi-character command.
 */
static void
start_mca(int action, const char *prompt, void *mlist, int cmdflags)
{
	mca = action;
	clear_bot();
	clear_cmd();
	cmd_putstr((char *)prompt);
	set_mlist(mlist, cmdflags);
}

int
in_mca(void)
{
	return (mca != 0 && mca != A_PREFIX);
}

/*
 * Set up the display to start a new search command.
 */
static void
mca_search(void)
{
	if (search_type & SRCH_FILTER)
		mca = A_FILTER;
	else if (search_type & SRCH_FORW)
		mca = A_F_SEARCH;
	else
		mca = A_B_SEARCH;

	clear_bot();
	clear_cmd();

	if (search_type & SRCH_NO_MATCH)
		cmd_putstr("Non-match ");
	if (search_type & SRCH_FIRST_FILE)
		cmd_putstr("First-file ");
	if (search_type & SRCH_PAST_EOF)
		cmd_putstr("EOF-ignore ");
	if (search_type & SRCH_NO_MOVE)
		cmd_putstr("Keep-pos ");
	if (search_type & SRCH_NO_REGEX)
		cmd_putstr("Regex-off ");

	if (search_type & SRCH_FILTER)
		cmd_putstr("&/");
	else if (search_type & SRCH_FORW)
		cmd_putstr("/");
	else
		cmd_putstr("?");
	set_mlist(ml_search, 0);
}

/*
 * Set up the display to start a new toggle-option command.
 */
static void
mca_opt_toggle(void)
{
	int no_prompt;
	int flag;
	char *dash;

	no_prompt = (optflag & OPT_NO_PROMPT);
	flag = (optflag & ~OPT_NO_PROMPT);
	dash = (flag == OPT_NO_TOGGLE) ? "_" : "-";

	mca = A_OPT_TOGGLE;
	clear_bot();
	clear_cmd();
	cmd_putstr(dash);
	if (optgetname)
		cmd_putstr(dash);
	if (no_prompt)
		cmd_putstr("(P)");
	switch (flag) {
	case OPT_UNSET:
		cmd_putstr("+");
		break;
	case OPT_SET:
		cmd_putstr("!");
		break;
	}
	set_mlist(NULL, 0);
}

/*
 * Execute a multicharacter command.
 */
static void
exec_mca(void)
{
	char *cbuf;

	cmd_exec();
	cbuf = get_cmdbuf();

	switch (mca) {
	case A_F_SEARCH:
	case A_B_SEARCH:
		multi_search(cbuf, (int)number);
		break;
	case A_FILTER:
		search_type ^= SRCH_NO_MATCH;
		set_filter_pattern(cbuf, search_type);
		break;
	case A_FIRSTCMD:
		/*
		 * Skip leading spaces or + signs in the string.
		 */
		while (*cbuf == '+' || *cbuf == ' ')
			cbuf++;
		free(every_first_cmd);
		if (*cbuf == '\0')
			every_first_cmd = NULL;
		else
			every_first_cmd = estrdup(cbuf);
		break;
	case A_OPT_TOGGLE:
		toggle_option(curropt, opt_lower, cbuf, optflag);
		curropt = NULL;
		break;
	case A_F_BRACKET:
		match_brac(cbuf[0], cbuf[1], 1, (int)number);
		break;
	case A_B_BRACKET:
		match_brac(cbuf[1], cbuf[0], 0, (int)number);
		break;
	case A_EXAMINE:
		if (secure)
			break;

		/* POSIX behavior, but possibly generally useful */
		if (strlen(cbuf) == 0) {
			reopen_curr_ifile();
			jump_back(1);
			break;
		}
		/* POSIX behavior - probably not generally useful */
		if (less_is_more && (strcmp(cbuf, "#") == 0)) {
			if (ntags()) {
				error("No previous file", NULL);
				break;
			}
			if (edit_prev(1)) {
				error("No previous file", NULL);
			} else {
				jump_back(1);
			}
			break;
		}
		edit_list(cbuf);
		/* If tag structure is loaded then clean it up. */
		cleantags();
		break;
	case A_PIPE:
		if (secure)
			break;
		(void) pipe_mark(pipec, cbuf);
		error("|done", NULL);
		break;
	}
}

/*
 * Is a character an erase or kill char?
 */
static int
is_erase_char(int c)
{
	return (c == erase_char || c == erase2_char || c == kill_char);
}

/*
 * Handle the first char of an option (after the initial dash).
 */
static int
mca_opt_first_char(int c)
{
	int no_prompt = (optflag & OPT_NO_PROMPT);
	int flag = (optflag & ~OPT_NO_PROMPT);
	if (flag == OPT_NO_TOGGLE) {
		switch (c) {
		case '_':
			/* "__" = long option name. */
			optgetname = TRUE;
			mca_opt_toggle();
			return (MCA_MORE);
		}
	} else {
		switch (c) {
		case '+':
			/* "-+" = UNSET. */
			optflag = no_prompt |
			    ((flag == OPT_UNSET) ? OPT_TOGGLE : OPT_UNSET);
			mca_opt_toggle();
			return (MCA_MORE);
		case '!':
			/* "-!" = SET */
			optflag = no_prompt |
			    ((flag == OPT_SET) ? OPT_TOGGLE : OPT_SET);
			mca_opt_toggle();
			return (MCA_MORE);
		case CONTROL('P'):
			optflag ^= OPT_NO_PROMPT;
			mca_opt_toggle();
			return (MCA_MORE);
		case '-':
			/* "--" = long option name. */
			optgetname = TRUE;
			mca_opt_toggle();
			return (MCA_MORE);
		}
	}
	/* Char was not handled here. */
	return (NO_MCA);
}

/*
 * Add a char to a long option name.
 * See if we've got a match for an option name yet.
 * If so, display the complete name and stop
 * accepting chars until user hits RETURN.
 */
static int
mca_opt_nonfirst_char(int c)
{
	char *p;
	char *oname;

	if (curropt != NULL) {
		/*
		 * Already have a match for the name.
		 * Don't accept anything but erase/kill.
		 */
		if (is_erase_char(c))
			return (MCA_DONE);
		return (MCA_MORE);
	}
	/*
	 * Add char to cmd buffer and try to match
	 * the option name.
	 */
	if (cmd_char(c) == CC_QUIT)
		return (MCA_DONE);
	p = get_cmdbuf();
	opt_lower = islower(p[0]);
	curropt = findopt_name(&p, &oname, NULL);
	if (curropt != NULL) {
		/*
		 * Got a match.
		 * Remember the option and
		 * display the full option name.
		 */
		cmd_reset();
		mca_opt_toggle();
		for (p = oname; *p != '\0'; p++) {
			c = *p;
			if (!opt_lower && islower(c))
				c = toupper(c);
			if (cmd_char(c) != CC_OK)
				return (MCA_DONE);
		}
	}
	return (MCA_MORE);
}

/*
 * Handle a char of an option toggle command.
 */
static int
mca_opt_char(int c)
{
	PARG parg;

	/*
	 * This may be a short option (single char),
	 * or one char of a long option name,
	 * or one char of the option parameter.
	 */
	if (curropt == NULL && len_cmdbuf() == 0) {
		int ret = mca_opt_first_char(c);
		if (ret != NO_MCA)
			return (ret);
	}
	if (optgetname) {
		/* We're getting a long option name.  */
		if (c != '\n' && c != '\r')
			return (mca_opt_nonfirst_char(c));
		if (curropt == NULL) {
			parg.p_string = get_cmdbuf();
			error("There is no --%s option", &parg);
			return (MCA_DONE);
		}
		optgetname = FALSE;
		cmd_reset();
	} else {
		if (is_erase_char(c))
			return (NO_MCA);
		if (curropt != NULL)
			/* We're getting the option parameter. */
			return (NO_MCA);
		curropt = findopt(c);
		if (curropt == NULL) {
			parg.p_string = propt(c);
			error("There is no %s option", &parg);
			return (MCA_DONE);
		}
	}
	/*
	 * If the option which was entered does not take a
	 * parameter, toggle the option immediately,
	 * so user doesn't have to hit RETURN.
	 */
	if ((optflag & ~OPT_NO_PROMPT) != OPT_TOGGLE ||
	    !opt_has_param(curropt)) {
		toggle_option(curropt, islower(c), "", optflag);
		return (MCA_DONE);
	}
	/*
	 * Display a prompt appropriate for the option parameter.
	 */
	start_mca(A_OPT_TOGGLE, opt_prompt(curropt), NULL, 0);
	return (MCA_MORE);
}

/*
 * Handle a char of a search command.
 */
static int
mca_search_char(int c)
{
	int flag = 0;

	/*
	 * Certain characters as the first char of
	 * the pattern have special meaning:
	 *	!  Toggle the NO_MATCH flag
	 *	*  Toggle the PAST_EOF flag
	 *	@  Toggle the FIRST_FILE flag
	 */
	if (len_cmdbuf() > 0)
		return (NO_MCA);

	switch (c) {
	case CONTROL('E'): /* ignore END of file */
	case '*':
		if (mca != A_FILTER)
			flag = SRCH_PAST_EOF;
		break;
	case CONTROL('F'): /* FIRST file */
	case '@':
		if (mca != A_FILTER)
			flag = SRCH_FIRST_FILE;
		break;
	case CONTROL('K'): /* KEEP position */
		if (mca != A_FILTER)
			flag = SRCH_NO_MOVE;
		break;
	case CONTROL('R'): /* Don't use REGULAR EXPRESSIONS */
		flag = SRCH_NO_REGEX;
		break;
	case CONTROL('N'): /* NOT match */
	case '!':
		flag = SRCH_NO_MATCH;
		break;
	}

	if (flag != 0) {
		search_type ^= flag;
		mca_search();
		return (MCA_MORE);
	}
	return (NO_MCA);
}

/*
 * Handle a character of a multi-character command.
 */
static int
mca_char(int c)
{
	int ret;

	switch (mca) {
	case 0:
		/*
		 * We're not in a multicharacter command.
		 */
		return (NO_MCA);

	case A_PREFIX:
		/*
		 * In the prefix of a command.
		 * This not considered a multichar command
		 * (even tho it uses cmdbuf, etc.).
		 * It is handled in the commands() switch.
		 */
		return (NO_MCA);

	case A_DIGIT:
		/*
		 * Entering digits of a number.
		 * Terminated by a non-digit.
		 */
		if (!((c >= '0' && c <= '9') || c == '.') && editchar(c,
		    EC_PEEK|EC_NOHISTORY|EC_NOCOMPLETE|EC_NORIGHTLEFT) ==
		    A_INVALID) {
			/*
			 * Not part of the number.
			 * End the number and treat this char
			 * as a normal command character.
			 */
			number = cmd_int(&fraction);
			mca = 0;
			cmd_accept();
			return (NO_MCA);
		}
		break;

	case A_OPT_TOGGLE:
		ret = mca_opt_char(c);
		if (ret != NO_MCA)
			return (ret);
		break;

	case A_F_SEARCH:
	case A_B_SEARCH:
	case A_FILTER:
		ret = mca_search_char(c);
		if (ret != NO_MCA)
			return (ret);
		break;

	default:
		/* Other multicharacter command. */
		break;
	}

	/*
	 * The multichar command is terminated by a newline.
	 */
	if (c == '\n' || c == '\r') {
		/*
		 * Execute the command.
		 */
		exec_mca();
		return (MCA_DONE);
	}

	/*
	 * Append the char to the command buffer.
	 */
	if (cmd_char(c) == CC_QUIT)
		/*
		 * Abort the multi-char command.
		 */
		return (MCA_DONE);

	if ((mca == A_F_BRACKET || mca == A_B_BRACKET) && len_cmdbuf() >= 2) {
		/*
		 * Special case for the bracket-matching commands.
		 * Execute the command after getting exactly two
		 * characters from the user.
		 */
		exec_mca();
		return (MCA_DONE);
	}

	/*
	 * Need another character.
	 */
	return (MCA_MORE);
}

/*
 * Discard any buffered file data.
 */
static void
clear_buffers(void)
{
	if (!(ch_getflags() & CH_CANSEEK))
		return;
	ch_flush();
	clr_linenum();
	clr_hilite();
}

/*
 * Make sure the screen is displayed.
 */
static void
make_display(void)
{
	/*
	 * If nothing is displayed yet, display starting from initial_scrpos.
	 */
	if (empty_screen()) {
		if (initial_scrpos.pos == -1)
			/*
			 * {{ Maybe this should be:
			 *    jump_loc(ch_zero(), jump_sline);
			 *    but this behavior seems rather unexpected
			 *    on the first screen. }}
			 */
			jump_loc(ch_zero(), 1);
		else
			jump_loc(initial_scrpos.pos, initial_scrpos.ln);
	} else if (screen_trashed) {
		int save_top_scroll = top_scroll;
		int save_ignore_eoi = ignore_eoi;
		top_scroll = 1;
		ignore_eoi = 0;
		if (screen_trashed == 2) {
			/*
			 * Special case used by ignore_eoi: re-open the input
			 * file and jump to the end of the file.
			 */
			reopen_curr_ifile();
			jump_forw();
		}
		repaint();
		top_scroll = save_top_scroll;
		ignore_eoi = save_ignore_eoi;
	}
}

/*
 * Display the appropriate prompt.
 */
static void
prompt(void)
{
	const char *p;

	if (ungot != NULL) {
		/*
		 * No prompt necessary if commands are from
		 * ungotten chars rather than from the user.
		 */
		return;
	}

	/*
	 * Make sure the screen is displayed.
	 */
	make_display();
	bottompos = position(BOTTOM_PLUS_ONE);

	/*
	 * If we've hit EOF on the last file and the -E flag is set, quit.
	 */
	if (get_quit_at_eof() == OPT_ONPLUS &&
	    eof_displayed() && !(ch_getflags() & CH_HELPFILE) &&
	    next_ifile(curr_ifile) == NULL)
		quit(QUIT_OK);

	/*
	 * If the entire file is displayed and the -F flag is set, quit.
	 */
	if (quit_if_one_screen &&
	    entire_file_displayed() && !(ch_getflags() & CH_HELPFILE) &&
	    next_ifile(curr_ifile) == NULL)
		quit(QUIT_OK);

	/*
	 * Select the proper prompt and display it.
	 */
	/*
	 * If the previous action was a forward movement,
	 * don't clear the bottom line of the display;
	 * just print the prompt since the forward movement guarantees
	 * that we're in the right position to display the prompt.
	 * Clearing the line could cause a problem: for example, if the last
	 * line displayed ended at the right screen edge without a newline,
	 * then clearing would clear the last displayed line rather than
	 * the prompt line.
	 */
	if (!forw_prompt)
		clear_bot();
	clear_cmd();
	forw_prompt = 0;
	p = prompt_string();
	if (is_filtering())
		putstr("& ");
	if (p == NULL || *p == '\0') {
		putchr(':');
	} else {
		at_enter(AT_STANDOUT);
		putstr(p);
		at_exit();
	}
	clear_eol();
}

/*
 * Display the less version message.
 */
void
dispversion(void)
{
	PARG parg;

	parg.p_string = version;
	error("less %s", &parg);
}

/*
 * Get command character.
 * The character normally comes from the keyboard,
 * but may come from ungotten characters
 * (characters previously given to ungetcc or ungetsc).
 */
int
getcc(void)
{
	if (unget_end) {
		/*
		 * We have just run out of ungotten chars.
		 */
		unget_end = 0;
		if (len_cmdbuf() == 0 || !empty_screen())
			return (getchr());
		/*
		 * Command is incomplete, so try to complete it.
		 */
		switch (mca) {
		case A_DIGIT:
			/*
			 * We have a number but no command.  Treat as #g.
			 */
			return ('g');

		case A_F_SEARCH:
		case A_B_SEARCH:
			/*
			 * We have "/string" but no newline.  Add the \n.
			 */
			return ('\n');

		default:
			/*
			 * Some other incomplete command.  Let user complete it.
			 */
			return (getchr());
		}
	}

	if (ungot == NULL) {
		/*
		 * Normal case: no ungotten chars, so get one from the user.
		 */
		return (getchr());
	}

	/*
	 * Return the next ungotten char.
	 */
	{
		struct ungot *ug = ungot;
		int c = ug->ug_char;
		ungot = ug->ug_next;
		free(ug);
		unget_end = (ungot == NULL);
		return (c);
	}
}

/*
 * "Unget" a command character.
 * The next getcc() will return this character.
 */
void
ungetcc(int c)
{
	struct ungot *ug = ecalloc(1, sizeof (struct ungot));

	ug->ug_char = c;
	ug->ug_next = ungot;
	ungot = ug;
	unget_end = 0;
}

/*
 * Unget a whole string of command characters.
 * The next sequence of getcc()'s will return this string.
 */
void
ungetsc(char *s)
{
	char *p;

	for (p = s + strlen(s) - 1; p >= s; p--)
		ungetcc(*p);
}

/*
 * Search for a pattern, possibly in multiple files.
 * If SRCH_FIRST_FILE is set, begin searching at the first file.
 * If SRCH_PAST_EOF is set, continue the search thru multiple files.
 */
static void
multi_search(char *pattern, int n)
{
	int nomore;
	IFILE save_ifile;
	int changed_file;

	changed_file = 0;
	save_ifile = save_curr_ifile();

	if (search_type & SRCH_FIRST_FILE) {
		/*
		 * Start at the first (or last) file
		 * in the command line list.
		 */
		if (search_type & SRCH_FORW)
			nomore = edit_first();
		else
			nomore = edit_last();
		if (nomore) {
			unsave_ifile(save_ifile);
			return;
		}
		changed_file = 1;
		search_type &= ~SRCH_FIRST_FILE;
	}

	for (;;) {
		n = search(search_type, pattern, n);
		/*
		 * The SRCH_NO_MOVE flag doesn't "stick": it gets cleared
		 * after being used once.  This allows "n" to work after
		 * using a /@@ search.
		 */
		search_type &= ~SRCH_NO_MOVE;
		if (n == 0) {
			/*
			 * Found it.
			 */
			unsave_ifile(save_ifile);
			return;
		}

		if (n < 0)
			/*
			 * Some kind of error in the search.
			 * Error message has been printed by search().
			 */
			break;

		if ((search_type & SRCH_PAST_EOF) == 0)
			/*
			 * We didn't find a match, but we're
			 * supposed to search only one file.
			 */
			break;
		/*
		 * Move on to the next file.
		 */
		if (search_type & SRCH_FORW)
			nomore = edit_next(1);
		else
			nomore = edit_prev(1);
		if (nomore)
			break;
		changed_file = 1;
	}

	/*
	 * Didn't find it.
	 * Print an error message if we haven't already.
	 */
	if (n > 0)
		error("Pattern not found", NULL);

	if (changed_file) {
		/*
		 * Restore the file we were originally viewing.
		 */
		reedit_ifile(save_ifile);
	} else {
		unsave_ifile(save_ifile);
	}
}

/*
 * Forward forever, or until a highlighted line appears.
 */
static int
forw_loop(int until_hilite)
{
	off_t curr_len;

	if (ch_getflags() & CH_HELPFILE)
		return (A_NOACTION);

	cmd_exec();
	jump_forw();
	curr_len = ch_length();
	highest_hilite = until_hilite ? curr_len : -1;
	ignore_eoi = 1;
	while (!any_sigs()) {
		if (until_hilite && highest_hilite > curr_len) {
			ring_bell();
			break;
		}
		make_display();
		forward(1, 0, 0);
	}
	ignore_eoi = 0;
	ch_set_eof();

	/*
	 * This gets us back in "F mode" after processing
	 * a non-abort signal (e.g. window-change).
	 */
	if (any_sigs() && !abort_sigs())
		return (until_hilite ? A_F_UNTIL_HILITE : A_F_FOREVER);

	return (A_NOACTION);
}

/*
 * Main command processor.
 * Accept and execute commands until a quit command.
 */
void
commands(void)
{
	int c = 0;
	int action;
	char *cbuf;
	int newaction;
	int save_search_type;
	char *extra;
	char tbuf[2];
	PARG parg;
	IFILE old_ifile;
	IFILE new_ifile;
	char *tagfile;

	search_type = SRCH_FORW;
	wscroll = (sc_height + 1) / 2;
	newaction = A_NOACTION;

	for (;;) {
		mca = 0;
		cmd_accept();
		number = 0;
		curropt = NULL;

		/*
		 * See if any signals need processing.
		 */
		if (any_sigs()) {
			psignals();
			if (quitting)
				quit(QUIT_SAVED_STATUS);
		}

		/*
		 * Display prompt and accept a character.
		 */
		cmd_reset();
		prompt();
		if (any_sigs())
			continue;
		if (newaction == A_NOACTION)
			c = getcc();

again:
		if (any_sigs())
			continue;

		if (newaction != A_NOACTION) {
			action = newaction;
			newaction = A_NOACTION;
		} else {
			/*
			 * If we are in a multicharacter command, call mca_char.
			 * Otherwise we call fcmd_decode to determine the
			 * action to be performed.
			 */
			if (mca)
				switch (mca_char(c)) {
				case MCA_MORE:
					/*
					 * Need another character.
					 */
					c = getcc();
					goto again;
				case MCA_DONE:
					/*
					 * Command has been handled by mca_char.
					 * Start clean with a prompt.
					 */
					continue;
				case NO_MCA:
					/*
					 * Not a multi-char command
					 * (at least, not anymore).
					 */
					break;
				}

			/*
			 * Decode the command character and decide what to do.
			 */
			if (mca) {
				/*
				 * We're in a multichar command.
				 * Add the character to the command buffer
				 * and display it on the screen.
				 * If the user backspaces past the start
				 * of the line, abort the command.
				 */
				if (cmd_char(c) == CC_QUIT || len_cmdbuf() == 0)
					continue;
				cbuf = get_cmdbuf();
			} else {
				/*
				 * Don't use cmd_char if we're starting fresh
				 * at the beginning of a command, because we
				 * don't want to echo the command until we know
				 * it is a multichar command.  We also don't
				 * want erase_char/kill_char to be treated
				 * as line editing characters.
				 */
				tbuf[0] = (char)c;
				tbuf[1] = '\0';
				cbuf = tbuf;
			}
			extra = NULL;
			action = fcmd_decode(cbuf, &extra);
			/*
			 * If an "extra" string was returned,
			 * process it as a string of command characters.
			 */
			if (extra != NULL)
				ungetsc(extra);
		}
		/*
		 * Clear the cmdbuf string.
		 * (But not if we're in the prefix of a command,
		 * because the partial command string is kept there.)
		 */
		if (action != A_PREFIX)
			cmd_reset();

		switch (action) {
		case A_DIGIT:
			/*
			 * First digit of a number.
			 */
			start_mca(A_DIGIT, ":", (void*)NULL, CF_QUIT_ON_ERASE);
			goto again;

		case A_F_WINDOW:
			/*
			 * Forward one window (and set the window size).
			 */
			if (number > 0)
				swindow = (int)number;
			/* FALLTHRU */
		case A_F_SCREEN:
			/*
			 * Forward one screen.
			 */
			if (number <= 0)
				number = get_swindow();
			cmd_exec();
			if (show_attn)
				set_attnpos(bottompos);
			forward((int)number, 0, 1);
			break;

		case A_B_WINDOW:
			/*
			 * Backward one window (and set the window size).
			 */
			if (number > 0)
				swindow = (int)number;
			/* FALLTHRU */
		case A_B_SCREEN:
			/*
			 * Backward one screen.
			 */
			if (number <= 0)
				number = get_swindow();
			cmd_exec();
			backward((int)number, 0, 1);
			break;

		case A_F_LINE:
			/*
			 * Forward N (default 1) line.
			 */
			if (number <= 0)
				number = 1;
			cmd_exec();
			if (show_attn == OPT_ONPLUS && number > 1)
				set_attnpos(bottompos);
			forward((int)number, 0, 0);
			break;

		case A_B_LINE:
			/*
			 * Backward N (default 1) line.
			 */
			if (number <= 0)
				number = 1;
			cmd_exec();
			backward((int)number, 0, 0);
			break;

		case A_F_SKIP:
			/*
			 * Skip ahead one screen, and then number lines.
			 */
			if (number <= 0) {
				number = get_swindow();
			} else {
				number += get_swindow();
			}
			cmd_exec();
			if (show_attn == OPT_ONPLUS)
				set_attnpos(bottompos);
			forward((int)number, 0, 1);
			break;

		case A_FF_LINE:
			/*
			 * Force forward N (default 1) line.
			 */
			if (number <= 0)
				number = 1;
			cmd_exec();
			if (show_attn == OPT_ONPLUS && number > 1)
				set_attnpos(bottompos);
			forward((int)number, 1, 0);
			break;

		case A_BF_LINE:
			/*
			 * Force backward N (default 1) line.
			 */
			if (number <= 0)
				number = 1;
			cmd_exec();
			backward((int)number, 1, 0);
			break;

		case A_FF_SCREEN:
			/*
			 * Force forward one screen.
			 */
			if (number <= 0)
				number = get_swindow();
			cmd_exec();
			if (show_attn == OPT_ONPLUS)
				set_attnpos(bottompos);
			forward((int)number, 1, 0);
			break;

		case A_F_FOREVER:
			/*
			 * Forward forever, ignoring EOF.
			 */
			newaction = forw_loop(0);
			break;

		case A_F_UNTIL_HILITE:
			newaction = forw_loop(1);
			break;

		case A_F_SCROLL:
			/*
			 * Forward N lines
			 * (default same as last 'd' or 'u' command).
			 */
			if (number > 0)
				wscroll = (int)number;
			cmd_exec();
			if (show_attn == OPT_ONPLUS)
				set_attnpos(bottompos);
			forward(wscroll, 0, 0);
			break;

		case A_B_SCROLL:
			/*
			 * Forward N lines
			 * (default same as last 'd' or 'u' command).
			 */
			if (number > 0)
				wscroll = (int)number;
			cmd_exec();
			backward(wscroll, 0, 0);
			break;

		case A_FREPAINT:
			/*
			 * Flush buffers, then repaint screen.
			 * Don't flush the buffers on a pipe!
			 */
			clear_buffers();
			/* FALLTHRU */
		case A_REPAINT:
			/*
			 * Repaint screen.
			 */
			cmd_exec();
			repaint();
			break;

		case A_GOLINE:
			/*
			 * Go to line N, default beginning of file.
			 */
			if (number <= 0)
				number = 1;
			cmd_exec();
			jump_back(number);
			break;

		case A_PERCENT:
			/*
			 * Go to a specified percentage into the file.
			 */
			if (number < 0) {
				number = 0;
				fraction = 0;
			}
			if (number > 100) {
				number = 100;
				fraction = 0;
			}
			cmd_exec();
			jump_percent((int)number, fraction);
			break;

		case A_GOEND:
			/*
			 * Go to line N, default end of file.
			 */
			cmd_exec();
			if (number <= 0)
				jump_forw();
			else
				jump_back(number);
			break;

		case A_GOPOS:
			/*
			 * Go to a specified byte position in the file.
			 */
			cmd_exec();
			if (number < 0)
				number = 0;
			jump_line_loc((off_t) number, jump_sline);
			break;

		case A_STAT:
			/*
			 * Print file name, etc.
			 */
			if (ch_getflags() & CH_HELPFILE)
				break;
			cmd_exec();
			parg.p_string = eq_message();
			error("%s", &parg);
			break;

		case A_VERSION:
			/*
			 * Print version number, without the "@(#)".
			 */
			cmd_exec();
			dispversion();
			break;

		case A_QUIT:
			/*
			 * Exit.
			 */
			if (curr_ifile != NULL &&
			    ch_getflags() & CH_HELPFILE) {
				/*
				 * Quit while viewing the help file
				 * just means return to viewing the
				 * previous file.
				 */
				hshift = save_hshift;
				if (edit_prev(1) == 0)
					break;
			}
			if (extra != NULL)
				quit(*extra);
			quit(QUIT_OK);
			break;

/*
 * Define abbreviation for a commonly used sequence below.
 */
#define	DO_SEARCH() \
			if (number <= 0) number = 1;	\
			mca_search();			\
			cmd_exec();			\
			multi_search(NULL, (int)number);


		case A_F_SEARCH:
			/*
			 * Search forward for a pattern.
			 * Get the first char of the pattern.
			 */
			search_type = SRCH_FORW;
			if (number <= 0)
				number = 1;
			mca_search();
			c = getcc();
			goto again;

		case A_B_SEARCH:
			/*
			 * Search backward for a pattern.
			 * Get the first char of the pattern.
			 */
			search_type = SRCH_BACK;
			if (number <= 0)
				number = 1;
			mca_search();
			c = getcc();
			goto again;

		case A_FILTER:
			search_type = SRCH_FORW | SRCH_FILTER;
			mca_search();
			c = getcc();
			goto again;

		case A_AGAIN_SEARCH:
			/*
			 * Repeat previous search.
			 */
			DO_SEARCH();
			break;

		case A_T_AGAIN_SEARCH:
			/*
			 * Repeat previous search, multiple files.
			 */
			search_type |= SRCH_PAST_EOF;
			DO_SEARCH();
			break;

		case A_REVERSE_SEARCH:
			/*
			 * Repeat previous search, in reverse direction.
			 */
			save_search_type = search_type;
			search_type = SRCH_REVERSE(search_type);
			DO_SEARCH();
			search_type = save_search_type;
			break;

		case A_T_REVERSE_SEARCH:
			/*
			 * Repeat previous search,
			 * multiple files in reverse direction.
			 */
			save_search_type = search_type;
			search_type = SRCH_REVERSE(search_type);
			search_type |= SRCH_PAST_EOF;
			DO_SEARCH();
			search_type = save_search_type;
			break;

		case A_UNDO_SEARCH:
			undo_search();
			break;

		case A_HELP:
			/*
			 * Help.
			 */
			if (ch_getflags() & CH_HELPFILE)
				break;
			if (ungot != NULL || unget_end) {
				error(less_is_more
				    ? "Invalid option -p h"
				    : "Invalid option ++h",
				    NULL);
				break;
			}
			cmd_exec();
			save_hshift = hshift;
			hshift = 0;
			(void) edit(helpfile());
			break;

		case A_EXAMINE:
			/*
			 * Edit a new file.  Get the filename.
			 */
			if (secure) {
				error("Command not available", NULL);
				break;
			}
			start_mca(A_EXAMINE, "Examine: ", ml_examine, 0);
			c = getcc();
			goto again;

		case A_VISUAL:
			/*
			 * Invoke an editor on the input file.
			 */
			if (secure) {
				error("Command not available", NULL);
				break;
			}
			if (ch_getflags() & CH_HELPFILE)
				break;
			if (strcmp(get_filename(curr_ifile), "-") == 0) {
				error("Cannot edit standard input", NULL);
				break;
			}
			/*
			 * Expand the editor prototype string
			 * and pass it to the system to execute.
			 * (Make sure the screen is displayed so the
			 * expansion of "+%lm" works.)
			 */
			make_display();
			cmd_exec();
			lsystem(pr_expand(editproto, 0), NULL);
			break;

		case A_NEXT_FILE:
			/*
			 * Examine next file.
			 */
			if (ntags()) {
				error("No next file", NULL);
				break;
			}
			if (number <= 0)
				number = 1;
			if (edit_next((int)number)) {
				if (get_quit_at_eof() && eof_displayed() &&
				    !(ch_getflags() & CH_HELPFILE))
					quit(QUIT_OK);
				parg.p_string = (number > 1) ? "(N-th) " : "";
				error("No %snext file", &parg);
			}
			break;

		case A_PREV_FILE:
			/*
			 * Examine previous file.
			 */
			if (ntags()) {
				error("No previous file", NULL);
				break;
			}
			if (number <= 0)
				number = 1;
			if (edit_prev((int)number)) {
				parg.p_string = (number > 1) ? "(N-th) " : "";
				error("No %sprevious file", &parg);
			}
			break;

		case A_NEXT_TAG:
			if (number <= 0)
				number = 1;
			cmd_exec();
			tagfile = nexttag((int)number);
			if (tagfile == NULL) {
				error("No next tag", NULL);
				break;
			}
			if (edit(tagfile) == 0) {
				off_t pos = tagsearch();
				if (pos != -1)
					jump_loc(pos, jump_sline);
			}
			break;

		case A_PREV_TAG:
			if (number <= 0)
				number = 1;
			tagfile = prevtag((int)number);
			if (tagfile == NULL) {
				error("No previous tag", NULL);
				break;
			}
			if (edit(tagfile) == 0) {
				off_t pos = tagsearch();
				if (pos != -1)
					jump_loc(pos, jump_sline);
			}
			break;

		case A_INDEX_FILE:
			/*
			 * Examine a particular file.
			 */
			if (number <= 0)
				number = 1;
			if (edit_index((int)number))
				error("No such file", NULL);
			break;

		case A_REMOVE_FILE:
			if (ch_getflags() & CH_HELPFILE)
				break;
			old_ifile = curr_ifile;
			new_ifile = getoff_ifile(curr_ifile);
			if (new_ifile == NULL) {
				ring_bell();
				break;
			}
			if (edit_ifile(new_ifile) != 0) {
				reedit_ifile(old_ifile);
				break;
			}
			del_ifile(old_ifile);
			break;

		case A_OPT_TOGGLE:
			optflag = OPT_TOGGLE;
			optgetname = FALSE;
			mca_opt_toggle();
			c = getcc();
			goto again;

		case A_DISP_OPTION:
			/*
			 * Report a flag setting.
			 */
			optflag = OPT_NO_TOGGLE;
			optgetname = FALSE;
			mca_opt_toggle();
			c = getcc();
			goto again;

		case A_FIRSTCMD:
			/*
			 * Set an initial command for new files.
			 */
			start_mca(A_FIRSTCMD, "+", NULL, 0);
			c = getcc();
			goto again;

		case A_SETMARK:
			/*
			 * Set a mark.
			 */
			if (ch_getflags() & CH_HELPFILE)
				break;
			start_mca(A_SETMARK, "mark: ", (void*)NULL, 0);
			c = getcc();
			if (c == erase_char || c == erase2_char ||
			    c == kill_char || c == '\n' || c == '\r')
				break;
			setmark(c);
			break;

		case A_GOMARK:
			/*
			 * Go to a mark.
			 */
			start_mca(A_GOMARK, "goto mark: ", (void*)NULL, 0);
			c = getcc();
			if (c == erase_char || c == erase2_char ||
			    c == kill_char || c == '\n' || c == '\r')
				break;
			cmd_exec();
			gomark(c);
			break;

		case A_PIPE:
			if (secure) {
				error("Command not available", NULL);
				break;
			}
			start_mca(A_PIPE, "|mark: ", (void*)NULL, 0);
			c = getcc();
			if (c == erase_char || c == erase2_char ||
			    c == kill_char)
				break;
			if (c == '\n' || c == '\r')
				c = '.';
			if (badmark(c))
				break;
			pipec = c;
			start_mca(A_PIPE, "!", ml_shell, 0);
			c = getcc();
			goto again;

		case A_B_BRACKET:
		case A_F_BRACKET:
			start_mca(action, "Brackets: ", (void*)NULL, 0);
			c = getcc();
			goto again;

		case A_LSHIFT:
			if (number > 0)
				shift_count = number;
			else
				number = (shift_count > 0) ?
				    shift_count : sc_width / 2;
			if (number > hshift)
				number = hshift;
			hshift -= number;
			screen_trashed = 1;
			break;

		case A_RSHIFT:
			if (number > 0)
				shift_count = number;
			else
				number = (shift_count > 0) ?
				    shift_count : sc_width / 2;
			hshift += number;
			screen_trashed = 1;
			break;

		case A_PREFIX:
			/*
			 * The command is incomplete (more chars are needed).
			 * Display the current char, so the user knows
			 * what's going on, and get another character.
			 */
			if (mca != A_PREFIX) {
				cmd_reset();
				start_mca(A_PREFIX, " ", (void*)NULL,
				    CF_QUIT_ON_ERASE);
				(void) cmd_char(c);
			}
			c = getcc();
			goto again;

		case A_NOACTION:
			break;

		default:
			ring_bell();
			break;
		}
	}
}