source: MondoRescue/branches/3.3/mindi-busybox/miscutils/less.c@ 3865

/* vi: set sw=4 ts=4: */
/*
 * Mini less implementation for busybox
 *
 * Copyright (C) 2005 by Rob Sullivan <cogito.ergo.cogito@gmail.com>
 *
 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
 */

/*
 * TODO:
 * - Add more regular expression support - search modifiers, certain matches, etc.
 * - Add more complex bracket searching - currently, nested brackets are
 *   not considered.
 * - Add support for "F" as an input. This causes less to act in
 *   a similar way to tail -f.
 * - Allow horizontal scrolling.
 *
 * Notes:
 * - the inp file pointer is used so that keyboard input works after
 *   redirected input has been read from stdin
 */

//config:config LESS
//config:   bool "less"
//config:   default y
//config:   help
//config:     'less' is a pager, meaning that it displays text files. It possesses
//config:     a wide array of features, and is an improvement over 'more'.
//config:
//config:config FEATURE_LESS_MAXLINES
//config:   int "Max number of input lines less will try to eat"
//config:   default 9999999
//config:   depends on LESS
//config:
//config:config FEATURE_LESS_BRACKETS
//config:   bool "Enable bracket searching"
//config:   default y
//config:   depends on LESS
//config:   help
//config:     This option adds the capability to search for matching left and right
//config:     brackets, facilitating programming.
//config:
//config:config FEATURE_LESS_FLAGS
//config:   bool "Enable -m/-M"
//config:   default y
//config:   depends on LESS
//config:   help
//config:     The -M/-m flag enables a more sophisticated status line.
//config:
//config:config FEATURE_LESS_TRUNCATE
//config:   bool "Enable -S"
//config:   default y
//config:   depends on LESS
//config:   help
//config:     The -S flag causes long lines to be truncated rather than
//config:     wrapped.
//config:
//config:config FEATURE_LESS_MARKS
//config:   bool "Enable marks"
//config:   default y
//config:   depends on LESS
//config:   help
//config:     Marks enable positions in a file to be stored for easy reference.
//config:
//config:config FEATURE_LESS_REGEXP
//config:   bool "Enable regular expressions"
//config:   default y
//config:   depends on LESS
//config:   help
//config:     Enable regular expressions, allowing complex file searches.
//config:
//config:config FEATURE_LESS_WINCH
//config:   bool "Enable automatic resizing on window size changes"
//config:   default y
//config:   depends on LESS
//config:   help
//config:     Makes less track window size changes.
//config:
//config:config FEATURE_LESS_ASK_TERMINAL
//config:   bool "Use 'tell me cursor position' ESC sequence to measure window"
//config:   default y
//config:   depends on FEATURE_LESS_WINCH
//config:   help
//config:     Makes less track window size changes.
//config:     If terminal size can't be retrieved and $LINES/$COLUMNS are not set,
//config:     this option makes less perform a last-ditch effort to find it:
//config:     position cursor to 999,999 and ask terminal to report real
//config:     cursor position using "ESC [ 6 n" escape sequence, then read stdin.
//config:
//config:     This is not clean but helps a lot on serial lines and such.
//config:
//config:config FEATURE_LESS_DASHCMD
//config:   bool "Enable flag changes ('-' command)"
//config:   default y
//config:   depends on LESS
//config:   help
//config:     This enables the ability to change command-line flags within
//config:     less itself ('-' keyboard command).
//config:
//config:config FEATURE_LESS_LINENUMS
//config:   bool "Enable dynamic switching of line numbers"
//config:   default y
//config:   depends on FEATURE_LESS_DASHCMD
//config:   help
//config:     Enables "-N" command.

//usage:#define less_trivial_usage
//usage:       "[-E" IF_FEATURE_LESS_REGEXP("I")IF_FEATURE_LESS_FLAGS("Mm")
//usage:       "N" IF_FEATURE_LESS_TRUNCATE("S") "h~] [FILE]..."
//usage:#define less_full_usage "\n\n"
//usage:       "View FILE (or stdin) one screenful at a time\n"
//usage:     "\n    -E  Quit once the end of a file is reached"
//usage:    IF_FEATURE_LESS_REGEXP(
//usage:     "\n    -I  Ignore case in all searches"
//usage:    )
//usage:    IF_FEATURE_LESS_FLAGS(
//usage:     "\n    -M,-m   Display status line with line numbers"
//usage:     "\n        and percentage through the file"
//usage:    )
//usage:     "\n    -N  Prefix line number to each line"
//usage:    IF_FEATURE_LESS_TRUNCATE(
//usage:     "\n    -S  Truncate long lines"
//usage:    )
//usage:     "\n    -~  Suppress ~s displayed past EOF"

#include <sched.h>  /* sched_yield() */

#include "libbb.h"
#include "common_bufsiz.h"
#if ENABLE_FEATURE_LESS_REGEXP
#include "xregex.h"
#endif


#define ESC "\033"
/* The escape codes for highlighted and normal text */
#define HIGHLIGHT   ESC"[7m"
#define NORMAL      ESC"[0m"
/* The escape code to home and clear to the end of screen */
#define CLEAR       ESC"[H\033[J"
/* The escape code to clear to the end of line */
#define CLEAR_2_EOL ESC"[K"

enum {
/* Absolute max of lines eaten */
    MAXLINES = CONFIG_FEATURE_LESS_MAXLINES,
/* This many "after the end" lines we will show (at max) */
    TILDES = 1,
};

/* Command line options */
enum {
    FLAG_E = 1 << 0,
    FLAG_M = 1 << 1,
    FLAG_m = 1 << 2,
    FLAG_N = 1 << 3,
    FLAG_TILDE = 1 << 4,
    FLAG_I = 1 << 5,
    FLAG_S = (1 << 6) * ENABLE_FEATURE_LESS_TRUNCATE,
/* hijack command line options variable for internal state vars */
    LESS_STATE_MATCH_BACKWARDS = 1 << 15,
};

#if !ENABLE_FEATURE_LESS_REGEXP
enum { pattern_valid = 0 };
#endif

struct globals {
    int cur_fline; /* signed */
    int kbd_fd;  /* fd to get input from */
    int less_gets_pos;
/* last position in last line, taking into account tabs */
    size_t last_line_pos;
    unsigned max_fline;
    unsigned max_lineno; /* this one tracks linewrap */
    unsigned max_displayed_line;
    unsigned width;
#if ENABLE_FEATURE_LESS_WINCH
    unsigned winch_counter;
#endif
    ssize_t eof_error; /* eof if 0, error if < 0 */
    ssize_t readpos;
    ssize_t readeof; /* must be signed */
    const char **buffer;
    const char **flines;
    const char *empty_line_marker;
    unsigned num_files;
    unsigned current_file;
    char *filename;
    char **files;
#if ENABLE_FEATURE_LESS_FLAGS
    int num_lines; /* a flag if < 0, line count if >= 0 */
# define REOPEN_AND_COUNT (-1)
# define REOPEN_STDIN     (-2)
# define NOT_REGULAR_FILE (-3)
#endif
#if ENABLE_FEATURE_LESS_MARKS
    unsigned num_marks;
    unsigned mark_lines[15][2];
#endif
#if ENABLE_FEATURE_LESS_REGEXP
    unsigned *match_lines;
    int match_pos; /* signed! */
    int wanted_match; /* signed! */
    int num_matches;
    regex_t pattern;
    smallint pattern_valid;
#endif
#if ENABLE_FEATURE_LESS_ASK_TERMINAL
    smallint winsize_err;
#endif
    smallint terminated;
    struct termios term_orig, term_less;
    char kbd_input[KEYCODE_BUFFER_SIZE];
};
#define G (*ptr_to_globals)
#define cur_fline           (G.cur_fline         )
#define kbd_fd              (G.kbd_fd            )
#define less_gets_pos       (G.less_gets_pos     )
#define last_line_pos       (G.last_line_pos     )
#define max_fline           (G.max_fline         )
#define max_lineno          (G.max_lineno        )
#define max_displayed_line  (G.max_displayed_line)
#define width               (G.width             )
#define winch_counter       (G.winch_counter     )
/* This one is 100% not cached by compiler on read access */
#define WINCH_COUNTER (*(volatile unsigned *)&winch_counter)
#define eof_error           (G.eof_error         )
#define readpos             (G.readpos           )
#define readeof             (G.readeof           )
#define buffer              (G.buffer            )
#define flines              (G.flines            )
#define empty_line_marker   (G.empty_line_marker )
#define num_files           (G.num_files         )
#define current_file        (G.current_file      )
#define filename            (G.filename          )
#define files               (G.files             )
#define num_lines           (G.num_lines         )
#define num_marks           (G.num_marks         )
#define mark_lines          (G.mark_lines        )
#if ENABLE_FEATURE_LESS_REGEXP
#define match_lines         (G.match_lines       )
#define match_pos           (G.match_pos         )
#define num_matches         (G.num_matches       )
#define wanted_match        (G.wanted_match      )
#define pattern             (G.pattern           )
#define pattern_valid       (G.pattern_valid     )
#endif
#define terminated          (G.terminated        )
#define term_orig           (G.term_orig         )
#define term_less           (G.term_less         )
#define kbd_input           (G.kbd_input         )
#define INIT_G() do { \
    SET_PTR_TO_GLOBALS(xzalloc(sizeof(G))); \
    less_gets_pos = -1; \
    empty_line_marker = "~"; \
    num_files = 1; \
    current_file = 1; \
    eof_error = 1; \
    terminated = 1; \
    IF_FEATURE_LESS_REGEXP(wanted_match = -1;) \
} while (0)

/* flines[] are lines read from stdin, each in malloc'ed buffer.
 * Line numbers are stored as uint32_t prepended to each line.
 * Pointer is adjusted so that flines[i] points directly past
 * line number. Accesor: */
#define MEMPTR(p) ((char*)(p) - 4)
#define LINENO(p) (*(uint32_t*)((p) - 4))


/* Reset terminal input to normal */
static void set_tty_cooked(void)
{
    fflush_all();
    tcsetattr(kbd_fd, TCSANOW, &term_orig);
}

/* Move the cursor to a position (x,y), where (0,0) is the
   top-left corner of the console */
static void move_cursor(int line, int row)
{
    printf(ESC"[%u;%uH", line, row);
}

static void clear_line(void)
{
    printf(ESC"[%u;0H" CLEAR_2_EOL, max_displayed_line + 2);
}

static void print_hilite(const char *str)
{
    printf(HIGHLIGHT"%s"NORMAL, str);
}

static void print_statusline(const char *str)
{
    clear_line();
    printf(HIGHLIGHT"%.*s"NORMAL, width - 1, str);
}

/* Exit the program gracefully */
static void less_exit(int code)
{
    set_tty_cooked();
    clear_line();
    if (code < 0)
        kill_myself_with_sig(- code); /* does not return */
    exit(code);
}

#if (ENABLE_FEATURE_LESS_DASHCMD && ENABLE_FEATURE_LESS_LINENUMS) \
 || ENABLE_FEATURE_LESS_WINCH
static void re_wrap(void)
{
    int w = width;
    int new_line_pos;
    int src_idx;
    int dst_idx;
    int new_cur_fline = 0;
    uint32_t lineno;
    char linebuf[w + 1];
    const char **old_flines = flines;
    const char *s;
    char **new_flines = NULL;
    char *d;

    if (option_mask32 & FLAG_N)
        w -= 8;

    src_idx = 0;
    dst_idx = 0;
    s = old_flines[0];
    lineno = LINENO(s);
    d = linebuf;
    new_line_pos = 0;
    while (1) {
        *d = *s;
        if (*d != '\0') {
            new_line_pos++;
            if (*d == '\t') { /* tab */
                new_line_pos += 7;
                new_line_pos &= (~7);
            }
            s++;
            d++;
            if (new_line_pos >= w) {
                int sz;
                /* new line is full, create next one */
                *d = '\0';
 next_new:
                sz = (d - linebuf) + 1; /* + 1: NUL */
                d = ((char*)xmalloc(sz + 4)) + 4;
                LINENO(d) = lineno;
                memcpy(d, linebuf, sz);
                new_flines = xrealloc_vector(new_flines, 8, dst_idx);
                new_flines[dst_idx] = d;
                dst_idx++;
                if (new_line_pos < w) {
                    /* if we came here thru "goto next_new" */
                    if (src_idx > max_fline)
                        break;
                    lineno = LINENO(s);
                }
                d = linebuf;
                new_line_pos = 0;
            }
            continue;
        }
        /* *d == NUL: old line ended, go to next old one */
        free(MEMPTR(old_flines[src_idx]));
        /* btw, convert cur_fline... */
        if (cur_fline == src_idx)
            new_cur_fline = dst_idx;
        src_idx++;
        /* no more lines? finish last new line (and exit the loop) */
        if (src_idx > max_fline)
            goto next_new;
        s = old_flines[src_idx];
        if (lineno != LINENO(s)) {
            /* this is not a continuation line!
             * create next _new_ line too */
            goto next_new;
        }
    }

    free(old_flines);
    flines = (const char **)new_flines;

    max_fline = dst_idx - 1;
    last_line_pos = new_line_pos;
    cur_fline = new_cur_fline;
    /* max_lineno is screen-size independent */
#if ENABLE_FEATURE_LESS_REGEXP
    pattern_valid = 0;
#endif
}
#endif

#if ENABLE_FEATURE_LESS_REGEXP
static void fill_match_lines(unsigned pos);
#else
#define fill_match_lines(pos) ((void)0)
#endif

static int at_end(void)
{
    return (option_mask32 & FLAG_S)
        ? !(cur_fline <= max_fline &&
            max_lineno > LINENO(flines[cur_fline]) + max_displayed_line)
        : !(max_fline > cur_fline + max_displayed_line);
}

/* Devilishly complex routine.
 *
 * Has to deal with EOF and EPIPE on input,
 * with line wrapping, with last line not ending in '\n'
 * (possibly not ending YET!), with backspace and tabs.
 * It reads input again if last time we got an EOF (thus supporting
 * growing files) or EPIPE (watching output of slow process like make).
 *
 * Variables used:
 * flines[] - array of lines already read. Linewrap may cause
 *      one source file line to occupy several flines[n].
 * flines[max_fline] - last line, possibly incomplete.
 * terminated - 1 if flines[max_fline] is 'terminated'
 *      (if there was '\n' [which isn't stored itself, we just remember
 *      that it was seen])
 * max_lineno - last line's number, this one doesn't increment
 *      on line wrap, only on "real" new lines.
 * readbuf[0..readeof-1] - small preliminary buffer.
 * readbuf[readpos] - next character to add to current line.
 * last_line_pos - screen line position of next char to be read
 *      (takes into account tabs and backspaces)
 * eof_error - < 0 error, == 0 EOF, > 0 not EOF/error
 *
 * "git log -p | less -m" on the kernel git tree is a good test for EAGAINs,
 * "/search on very long input" and "reaching max line count" corner cases.
 */
static void read_lines(void)
{
    char *current_line, *p;
    int w = width;
    char last_terminated = terminated;
    time_t last_time = 0;
    int retry_EAGAIN = 2;
#if ENABLE_FEATURE_LESS_REGEXP
    unsigned old_max_fline = max_fline;
#endif

#define readbuf bb_common_bufsiz1
    setup_common_bufsiz();

    /* (careful: max_fline can be -1) */
    if (max_fline + 1 > MAXLINES)
        return;

    if (option_mask32 & FLAG_N)
        w -= 8;

    p = current_line = ((char*)xmalloc(w + 5)) + 4;
    if (!last_terminated) {
        const char *cp = flines[max_fline];
        p = stpcpy(p, cp);
        free(MEMPTR(cp));
        /* last_line_pos is still valid from previous read_lines() */
    } else {
        max_fline++;
        last_line_pos = 0;
    }

    while (1) { /* read lines until we reach cur_fline or wanted_match */
        *p = '\0';
        terminated = 0;
        while (1) { /* read chars until we have a line */
            char c;
            /* if no unprocessed chars left, eat more */
            if (readpos >= readeof) {
                int flags = ndelay_on(0);

                while (1) {
                    time_t t;

                    errno = 0;
                    eof_error = safe_read(STDIN_FILENO, readbuf, COMMON_BUFSIZE);
                    if (errno != EAGAIN)
                        break;
                    t = time(NULL);
                    if (t != last_time) {
                        last_time = t;
                        if (--retry_EAGAIN < 0)
                            break;
                    }
                    sched_yield();
                }
                fcntl(0, F_SETFL, flags); /* ndelay_off(0) */
                readpos = 0;
                readeof = eof_error;
                if (eof_error <= 0)
                    goto reached_eof;
                retry_EAGAIN = 1;
            }
            c = readbuf[readpos];
            /* backspace? [needed for manpages] */
            /* <tab><bs> is (a) insane and */
            /* (b) harder to do correctly, so we refuse to do it */
            if (c == '\x8' && last_line_pos && p[-1] != '\t') {
                readpos++; /* eat it */
                last_line_pos--;
            /* was buggy (p could end up <= current_line)... */
                *--p = '\0';
                continue;
            }
            {
                size_t new_last_line_pos = last_line_pos + 1;
                if (c == '\t') {
                    new_last_line_pos += 7;
                    new_last_line_pos &= (~7);
                }
                if ((int)new_last_line_pos > w)
                    break;
                last_line_pos = new_last_line_pos;
            }
            /* ok, we will eat this char */
            readpos++;
            if (c == '\n') {
                terminated = 1;
                last_line_pos = 0;
                break;
            }
            /* NUL is substituted by '\n'! */
            if (c == '\0') c = '\n';
            *p++ = c;
            *p = '\0';
        } /* end of "read chars until we have a line" loop */
#if 0
//BUG: also triggers on this:
// { printf "\nfoo\n"; sleep 1; printf "\nbar\n"; } | less
// (resulting in lost empty line between "foo" and "bar" lines)
// the "terminated" logic needs fixing (or explaining)
        /* Corner case: linewrap with only "" wrapping to next line */
        /* Looks ugly on screen, so we do not store this empty line */
        if (!last_terminated && !current_line[0]) {
            last_terminated = 1;
            max_lineno++;
            continue;
        }
#endif
 reached_eof:
        last_terminated = terminated;
        flines = xrealloc_vector(flines, 8, max_fline);

        flines[max_fline] = (char*)xrealloc(MEMPTR(current_line), strlen(current_line) + 1 + 4) + 4;
        LINENO(flines[max_fline]) = max_lineno;
        if (terminated)
            max_lineno++;

        if (max_fline >= MAXLINES) {
            eof_error = 0; /* Pretend we saw EOF */
            break;
        }
        if (!at_end()) {
#if !ENABLE_FEATURE_LESS_REGEXP
            break;
#else
            if (wanted_match >= num_matches) { /* goto_match called us */
                fill_match_lines(old_max_fline);
                old_max_fline = max_fline;
            }
            if (wanted_match < num_matches)
                break;
#endif
        }
        if (eof_error <= 0) {
            break;
        }
        max_fline++;
        current_line = ((char*)xmalloc(w + 5)) + 4;
        p = current_line;
        last_line_pos = 0;
    } /* end of "read lines until we reach cur_fline" loop */

    if (eof_error < 0) {
        if (errno == EAGAIN) {
            eof_error = 1;
        } else {
            print_statusline(bb_msg_read_error);
        }
    }
#if ENABLE_FEATURE_LESS_FLAGS
    else if (eof_error == 0)
        num_lines = max_lineno;
#endif

    fill_match_lines(old_max_fline);
#if ENABLE_FEATURE_LESS_REGEXP
    /* prevent us from being stuck in search for a match */
    wanted_match = -1;
#endif
#undef readbuf
}

#if ENABLE_FEATURE_LESS_FLAGS
static int safe_lineno(int fline)
{
    if (fline >= max_fline)
        fline = max_fline - 1;

    /* also catches empty file (max_fline == 0) */
    if (fline < 0)
        return 0;

    return LINENO(flines[fline]) + 1;
}

/* count number of lines in file */
static void update_num_lines(void)
{
    int count, fd;
    struct stat stbuf;
    ssize_t len, i;
    char buf[4096];

    /* only do this for regular files */
    if (num_lines == REOPEN_AND_COUNT || num_lines == REOPEN_STDIN) {
        count = 0;
        fd = open("/proc/self/fd/0", O_RDONLY);
        if (fd < 0 && num_lines == REOPEN_AND_COUNT) {
            /* "filename" is valid only if REOPEN_AND_COUNT */
            fd = open(filename, O_RDONLY);
        }
        if (fd < 0) {
            /* somebody stole my file! */
            num_lines = NOT_REGULAR_FILE;
            return;
        }
        if (fstat(fd, &stbuf) != 0 || !S_ISREG(stbuf.st_mode)) {
            num_lines = NOT_REGULAR_FILE;
            goto do_close;
        }
        while ((len = safe_read(fd, buf, sizeof(buf))) > 0) {
            for (i = 0; i < len; ++i) {
                if (buf[i] == '\n' && ++count == MAXLINES)
                    goto done;
            }
        }
 done:
        num_lines = count;
 do_close:
        close(fd);
    }
}

/* Print a status line if -M was specified */
static void m_status_print(void)
{
    int first, last;
    unsigned percent;

    if (less_gets_pos >= 0) /* don't touch statusline while input is done! */
        return;

    clear_line();
    printf(HIGHLIGHT"%s", filename);
    if (num_files > 1)
        printf(" (file %i of %i)", current_file, num_files);

    first = safe_lineno(cur_fline);
    last = (option_mask32 & FLAG_S)
            ? MIN(first + max_displayed_line, max_lineno)
            : safe_lineno(cur_fline + max_displayed_line);
    printf(" lines %i-%i", first, last);

    update_num_lines();
    if (num_lines >= 0)
        printf("/%i", num_lines);

    if (at_end()) {
        printf(" (END)");
        if (num_files > 1 && current_file != num_files)
            printf(" - next: %s", files[current_file]);
    } else if (num_lines > 0) {
        percent = (100 * last + num_lines/2) / num_lines;
        printf(" %i%%", percent <= 100 ? percent : 100);
    }
    printf(NORMAL);
}
#endif

/* Print the status line */
static void status_print(void)
{
    const char *p;

    if (less_gets_pos >= 0) /* don't touch statusline while input is done! */
        return;

    /* Change the status if flags have been set */
#if ENABLE_FEATURE_LESS_FLAGS
    if (option_mask32 & (FLAG_M|FLAG_m)) {
        m_status_print();
        return;
    }
    /* No flags set */
#endif

    clear_line();
    if (cur_fline && !at_end()) {
        bb_putchar(':');
        return;
    }
    p = "(END)";
    if (!cur_fline)
        p = filename;
    if (num_files > 1) {
        printf(HIGHLIGHT"%s (file %i of %i)"NORMAL,
                p, current_file, num_files);
        return;
    }
    print_hilite(p);
}

static const char controls[] ALIGN1 =
    /* NUL: never encountered; TAB: not converted */
    /**/"\x01\x02\x03\x04\x05\x06\x07\x08"  "\x0a\x0b\x0c\x0d\x0e\x0f"
    "\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f"
    "\x7f\x9b"; /* DEL and infamous Meta-ESC :( */
static const char ctrlconv[] ALIGN1 =
    /* why 40 instead of 4a below? - it is a replacement for '\n'.
     * '\n' is a former NUL - we subst it with @, not J */
    "\x40\x41\x42\x43\x44\x45\x46\x47\x48\x49\x40\x4b\x4c\x4d\x4e\x4f"
    "\x50\x51\x52\x53\x54\x55\x56\x57\x58\x59\x5a\x5b\x5c\x5d\x5e\x5f";

static void print_lineno(const char *line)
{
    const char *fmt = "        ";
    unsigned n = n; /* for compiler */

    if (line != empty_line_marker) {
        /* Width of 7 preserves tab spacing in the text */
        fmt = "%7u ";
        n = LINENO(line) + 1;
        if (n > 9999999 && MAXLINES > 9999999) {
            n %= 10000000;
            fmt = "%07u ";
        }
    }
    printf(fmt, n);
}


#if ENABLE_FEATURE_LESS_REGEXP
static void print_found(const char *line)
{
    int match_status;
    int eflags;
    char *growline;
    regmatch_t match_structs;

    char buf[width+1];
    const char *str = line;
    char *p = buf;
    size_t n;

    while (*str) {
        n = strcspn(str, controls);
        if (n) {
            if (!str[n]) break;
            memcpy(p, str, n);
            p += n;
            str += n;
        }
        n = strspn(str, controls);
        memset(p, '.', n);
        p += n;
        str += n;
    }
    strcpy(p, str);

    /* buf[] holds quarantined version of str */

    /* Each part of the line that matches has the HIGHLIGHT
     * and NORMAL escape sequences placed around it.
     * NB: we regex against line, but insert text
     * from quarantined copy (buf[]) */
    str = buf;
    growline = NULL;
    eflags = 0;
    goto start;

    while (match_status == 0) {
        char *new = xasprintf("%s%.*s"HIGHLIGHT"%.*s"NORMAL,
                growline ? growline : "",
                (int)match_structs.rm_so, str,
                (int)(match_structs.rm_eo - match_structs.rm_so),
                        str + match_structs.rm_so);
        free(growline);
        growline = new;
        str += match_structs.rm_eo;
        line += match_structs.rm_eo;
        eflags = REG_NOTBOL;
 start:
        /* Most of the time doesn't find the regex, optimize for that */
        match_status = regexec(&pattern, line, 1, &match_structs, eflags);
        /* if even "" matches, treat it as "not a match" */
        if (match_structs.rm_so >= match_structs.rm_eo)
            match_status = 1;
    }

    printf("%s%s\n", growline ? growline : "", str);
    free(growline);
}
#else
void print_found(const char *line);
#endif

static void print_ascii(const char *str)
{
    char buf[width+1];
    char *p;
    size_t n;

    while (*str) {
        n = strcspn(str, controls);
        if (n) {
            if (!str[n]) break;
            printf("%.*s", (int) n, str);
            str += n;
        }
        n = strspn(str, controls);
        p = buf;
        do {
            if (*str == 0x7f)
                *p++ = '?';
            else if (*str == (char)0x9b)
            /* VT100's CSI, aka Meta-ESC. Who's inventor? */
            /* I want to know who committed this sin */
                *p++ = '{';
            else
                *p++ = ctrlconv[(unsigned char)*str];
            str++;
        } while (--n);
        *p = '\0';
        print_hilite(buf);
    }
    puts(str);
}

/* Print the buffer */
static void buffer_print(void)
{
    unsigned i;

    move_cursor(0, 0);
    for (i = 0; i <= max_displayed_line; i++) {
        printf(CLEAR_2_EOL);
        if (option_mask32 & FLAG_N)
            print_lineno(buffer[i]);
        if (pattern_valid)
            print_found(buffer[i]);
        else
            print_ascii(buffer[i]);
    }
    if ((option_mask32 & FLAG_E)
     && eof_error <= 0
     && (max_fline - cur_fline) <= max_displayed_line
    ) {
        less_exit(EXIT_SUCCESS);
    }
    status_print();
}

static void buffer_fill_and_print(void)
{
    unsigned i;
#if ENABLE_FEATURE_LESS_TRUNCATE
    int fpos = cur_fline;

    if (option_mask32 & FLAG_S) {
        /* Go back to the beginning of this line */
        while (fpos && LINENO(flines[fpos]) == LINENO(flines[fpos-1]))
            fpos--;
    }

    i = 0;
    while (i <= max_displayed_line && fpos <= max_fline) {
        int lineno = LINENO(flines[fpos]);
        buffer[i] = flines[fpos];
        i++;
        do {
            fpos++;
        } while ((fpos <= max_fline)
              && (option_mask32 & FLAG_S)
              && lineno == LINENO(flines[fpos])
        );
    }
#else
    for (i = 0; i <= max_displayed_line && cur_fline + i <= max_fline; i++) {
        buffer[i] = flines[cur_fline + i];
    }
#endif
    for (; i <= max_displayed_line; i++) {
        buffer[i] = empty_line_marker;
    }
    buffer_print();
}

/* move cur_fline to a given line number, reading lines if necessary */
static void goto_lineno(int target)
{
    if (target <= 0 ) {
        cur_fline = 0;
    }
    else if (target > LINENO(flines[cur_fline])) {
 retry:
        while (LINENO(flines[cur_fline]) != target && cur_fline < max_fline)
            ++cur_fline;
        /* target not reached but more input is available */
        if (LINENO(flines[cur_fline]) != target && eof_error > 0) {
            read_lines();
            goto retry;
        }
    }
    else {
        /* search backwards through already-read lines */
        while (LINENO(flines[cur_fline]) != target && cur_fline > 0)
            --cur_fline;
    }
}

static void cap_cur_fline(void)
{
    if ((option_mask32 & FLAG_S)) {
        if (cur_fline > max_fline)
            cur_fline = max_fline;
        if (LINENO(flines[cur_fline]) + max_displayed_line > max_lineno + TILDES) {
            goto_lineno(max_lineno - max_displayed_line + TILDES);
            read_lines();
        }
    }
    else {
        if (cur_fline + max_displayed_line > max_fline + TILDES)
            cur_fline = max_fline - max_displayed_line + TILDES;
        if (cur_fline < 0)
            cur_fline = 0;
    }
}

/* Move the buffer up and down in the file in order to scroll */
static void buffer_down(int nlines)
{
    if ((option_mask32 & FLAG_S))
        goto_lineno(LINENO(flines[cur_fline]) + nlines);
    else
        cur_fline += nlines;
    read_lines();
    cap_cur_fline();
    buffer_fill_and_print();
}

static void buffer_up(int nlines)
{
    if ((option_mask32 & FLAG_S)) {
        goto_lineno(LINENO(flines[cur_fline]) - nlines);
    }
    else {
        cur_fline -= nlines;
        if (cur_fline < 0)
            cur_fline = 0;
    }
    read_lines();
    buffer_fill_and_print();
}

/* display a given line where the argument can be either an index into
 * the flines array or a line number */
static void buffer_to_line(int linenum, int is_lineno)
{
    if (linenum <= 0)
        cur_fline = 0;
    else if (is_lineno)
        goto_lineno(linenum);
    else
        cur_fline = linenum;
    read_lines();
    cap_cur_fline();
    buffer_fill_and_print();
}

static void buffer_line(int linenum)
{
    buffer_to_line(linenum, FALSE);
}

static void buffer_lineno(int lineno)
{
    buffer_to_line(lineno, TRUE);
}

static void open_file_and_read_lines(void)
{
    if (filename) {
        xmove_fd(xopen(filename, O_RDONLY), STDIN_FILENO);
#if ENABLE_FEATURE_LESS_FLAGS
        num_lines = REOPEN_AND_COUNT;
#endif
    } else {
        /* "less" with no arguments in argv[] */
        /* For status line only */
        filename = xstrdup(bb_msg_standard_input);
#if ENABLE_FEATURE_LESS_FLAGS
        num_lines = REOPEN_STDIN;
#endif
    }
    readpos = 0;
    readeof = 0;
    last_line_pos = 0;
    terminated = 1;
    read_lines();
}

/* Reinitialize everything for a new file - free the memory and start over */
static void reinitialize(void)
{
    unsigned i;

    if (flines) {
        for (i = 0; i <= max_fline; i++)
            free(MEMPTR(flines[i]));
        free(flines);
        flines = NULL;
    }

    max_fline = -1;
    cur_fline = 0;
    max_lineno = 0;
    open_file_and_read_lines();
#if ENABLE_FEATURE_LESS_ASK_TERMINAL
    if (G.winsize_err)
        printf("\033[999;999H" "\033[6n");
#endif
    buffer_fill_and_print();
}

static int64_t getch_nowait(void)
{
    int rd;
    int64_t key64;
    struct pollfd pfd[2];

    pfd[0].fd = STDIN_FILENO;
    pfd[0].events = POLLIN;
    pfd[1].fd = kbd_fd;
    pfd[1].events = POLLIN;
 again:
    tcsetattr(kbd_fd, TCSANOW, &term_less);
    /* NB: select/poll returns whenever read will not block. Therefore:
     * if eof is reached, select/poll will return immediately
     * because read will immediately return 0 bytes.
     * Even if select/poll says that input is available, read CAN block
     * (switch fd into O_NONBLOCK'ed mode to avoid it)
     */
    rd = 1;
    /* Are we interested in stdin? */
    if (at_end()) {
        if (eof_error > 0) /* did NOT reach eof yet */
            rd = 0; /* yes, we are interested in stdin */
    }
    /* Position cursor if line input is done */
    if (less_gets_pos >= 0)
        move_cursor(max_displayed_line + 2, less_gets_pos + 1);
    fflush_all();

    if (kbd_input[0] == 0) { /* if nothing is buffered */
#if ENABLE_FEATURE_LESS_WINCH
        while (1) {
            int r;
            /* NB: SIGWINCH interrupts poll() */
            r = poll(pfd + rd, 2 - rd, -1);
            if (/*r < 0 && errno == EINTR &&*/ winch_counter)
                return '\\'; /* anything which has no defined function */
            if (r) break;
        }
#else
        safe_poll(pfd + rd, 2 - rd, -1);
#endif
    }

    /* We have kbd_fd in O_NONBLOCK mode, read inside read_key()
     * would not block even if there is no input available */
    key64 = read_key(kbd_fd, kbd_input, /*timeout off:*/ -2);
    if ((int)key64 == -1) {
        if (errno == EAGAIN) {
            /* No keyboard input available. Since poll() did return,
             * we should have input on stdin */
            read_lines();
            buffer_fill_and_print();
            goto again;
        }
        /* EOF/error (ssh session got killed etc) */
        less_exit(0);
    }
    set_tty_cooked();
    return key64;
}

/* Grab a character from input without requiring the return key.
 * May return KEYCODE_xxx values.
 * Note that this function works best with raw input. */
static int64_t less_getch(int pos)
{
    int64_t key64;
    int key;

 again:
    less_gets_pos = pos;
    key = key64 = getch_nowait();
    less_gets_pos = -1;

    /* Discard Ctrl-something chars.
     * (checking only lower 32 bits is a size optimization:
     * upper 32 bits are used only by KEYCODE_CURSOR_POS)
     */
    if (key >= 0 && key < ' ' && key != 0x0d && key != 8)
        goto again;

    return key64;
}

static char* less_gets(int sz)
{
    int c;
    unsigned i = 0;
    char *result = xzalloc(1);

    while (1) {
        c = '\0';
        less_gets_pos = sz + i;
        c = getch_nowait();
        if (c == 0x0d) {
            result[i] = '\0';
            less_gets_pos = -1;
            return result;
        }
        if (c == 0x7f)
            c = 8;
        if (c == 8 && i) {
            printf("\x8 \x8");
            i--;
        }
        if (c < ' ') /* filters out KEYCODE_xxx too (<0) */
            continue;
        if (i >= width - sz - 1)
            continue; /* len limit */
        bb_putchar(c);
        result[i++] = c;
        result = xrealloc(result, i+1);
    }
}

static void examine_file(void)
{
    char *new_fname;

    print_statusline("Examine: ");
    new_fname = less_gets(sizeof("Examine: ") - 1);
    if (!new_fname[0]) {
        status_print();
 err:
        free(new_fname);
        return;
    }
    if (access(new_fname, R_OK) != 0) {
        print_statusline("Cannot read this file");
        goto err;
    }
    free(filename);
    filename = new_fname;
    /* files start by = argv. why we assume that argv is infinitely long??
    files[num_files] = filename;
    current_file = num_files + 1;
    num_files++; */
    files[0] = filename;
    num_files = current_file = 1;
    reinitialize();
}

/* This function changes the file currently being paged. direction can be one of the following:
 * -1: go back one file
 *  0: go to the first file
 *  1: go forward one file */
static void change_file(int direction)
{
    if (current_file != ((direction > 0) ? num_files : 1)) {
        current_file = direction ? current_file + direction : 1;
        free(filename);
        filename = xstrdup(files[current_file - 1]);
        reinitialize();
    } else {
        print_statusline(direction > 0 ? "No next file" : "No previous file");
    }
}

static void remove_current_file(void)
{
    unsigned i;

    if (num_files < 2)
        return;

    if (current_file != 1) {
        change_file(-1);
        for (i = 3; i <= num_files; i++)
            files[i - 2] = files[i - 1];
        num_files--;
    } else {
        change_file(1);
        for (i = 2; i <= num_files; i++)
            files[i - 2] = files[i - 1];
        num_files--;
        current_file--;
    }
}

static void colon_process(void)
{
    int keypress;

    /* Clear the current line and print a prompt */
    print_statusline(" :");

    keypress = less_getch(2);
    switch (keypress) {
    case 'd':
        remove_current_file();
        break;
    case 'e':
        examine_file();
        break;
#if ENABLE_FEATURE_LESS_FLAGS
    case 'f':
        m_status_print();
        break;
#endif
    case 'n':
        change_file(1);
        break;
    case 'p':
        change_file(-1);
        break;
    case 'q':
        less_exit(EXIT_SUCCESS);
        break;
    case 'x':
        change_file(0);
        break;
    }
}

#if ENABLE_FEATURE_LESS_REGEXP
static void normalize_match_pos(int match)
{
    if (match >= num_matches)
        match = num_matches - 1;
    if (match < 0)
        match = 0;
    match_pos = match;
}

static void goto_match(int match)
{
    if (!pattern_valid)
        return;
    if (match < 0)
        match = 0;
    /* Try to find next match if eof isn't reached yet */
    if (match >= num_matches && eof_error > 0) {
        wanted_match = match; /* "I want to read until I see N'th match" */
        read_lines();
    }
    if (num_matches) {
        normalize_match_pos(match);
        buffer_line(match_lines[match_pos]);
    } else {
        print_statusline("No matches found");
    }
}

static void fill_match_lines(unsigned pos)
{
    if (!pattern_valid)
        return;
    /* Run the regex on each line of the current file */
    while (pos <= max_fline) {
        /* If this line matches */
        if (regexec(&pattern, flines[pos], 0, NULL, 0) == 0
        /* and we didn't match it last time */
         && !(num_matches && match_lines[num_matches-1] == pos)
        ) {
            match_lines = xrealloc_vector(match_lines, 4, num_matches);
            match_lines[num_matches++] = pos;
        }
        pos++;
    }
}

static void regex_process(void)
{
    char *uncomp_regex, *err;

    /* Reset variables */
    free(match_lines);
    match_lines = NULL;
    match_pos = 0;
    num_matches = 0;
    if (pattern_valid) {
        regfree(&pattern);
        pattern_valid = 0;
    }

    /* Get the uncompiled regular expression from the user */
    clear_line();
    bb_putchar((option_mask32 & LESS_STATE_MATCH_BACKWARDS) ? '?' : '/');
    uncomp_regex = less_gets(1);
    if (!uncomp_regex[0]) {
        free(uncomp_regex);
        buffer_print();
        return;
    }

    /* Compile the regex and check for errors */
    err = regcomp_or_errmsg(&pattern, uncomp_regex,
                (option_mask32 & FLAG_I) ? REG_ICASE : 0);
    free(uncomp_regex);
    if (err) {
        print_statusline(err);
        free(err);
        return;
    }

    pattern_valid = 1;
    match_pos = 0;
    fill_match_lines(0);
    while (match_pos < num_matches) {
        if ((int)match_lines[match_pos] > cur_fline)
            break;
        match_pos++;
    }
    if (option_mask32 & LESS_STATE_MATCH_BACKWARDS)
        match_pos--;

    /* It's possible that no matches are found yet.
     * goto_match() will read input looking for match,
     * if needed */
    goto_match(match_pos);
}
#endif

static void number_process(int first_digit)
{
    unsigned i;
    int num;
    int keypress;
    char num_input[sizeof(int)*4]; /* more than enough */

    num_input[0] = first_digit;

    /* Clear the current line, print a prompt, and then print the digit */
    clear_line();
    printf(":%c", first_digit);

    /* Receive input until a letter is given */
    i = 1;
    while (i < sizeof(num_input)-1) {
        keypress = less_getch(i + 1);
        if ((unsigned)keypress > 255 || !isdigit(keypress))
            break;
        num_input[i] = keypress;
        bb_putchar(keypress);
        i++;
    }

    num_input[i] = '\0';
    num = bb_strtou(num_input, NULL, 10);
    /* on format error, num == -1 */
    if (num < 1 || num > MAXLINES) {
        buffer_print();
        return;
    }

    /* We now know the number and the letter entered, so we process them */
    switch (keypress) {
    case KEYCODE_DOWN: case 'z': case 'd': case 'e': case ' ': case '\015':
        buffer_down(num);
        break;
    case KEYCODE_UP: case 'b': case 'w': case 'y': case 'u':
        buffer_up(num);
        break;
    case 'g': case '<': case 'G': case '>':
        buffer_lineno(num - 1);
        break;
    case 'p': case '%':
#if ENABLE_FEATURE_LESS_FLAGS
        update_num_lines();
        num = num * (num_lines > 0 ? num_lines : max_lineno) / 100;
#else
        num = num * max_lineno / 100;
#endif
        buffer_lineno(num);
        break;
#if ENABLE_FEATURE_LESS_REGEXP
    case 'n':
        goto_match(match_pos + num);
        break;
    case '/':
        option_mask32 &= ~LESS_STATE_MATCH_BACKWARDS;
        regex_process();
        break;
    case '?':
        option_mask32 |= LESS_STATE_MATCH_BACKWARDS;
        regex_process();
        break;
#endif
    }
}

#if ENABLE_FEATURE_LESS_DASHCMD
static void flag_change(void)
{
    int keypress;

    clear_line();
    bb_putchar('-');
    keypress = less_getch(1);

    switch (keypress) {
    case 'M':
        option_mask32 ^= FLAG_M;
        break;
    case 'm':
        option_mask32 ^= FLAG_m;
        break;
    case 'E':
        option_mask32 ^= FLAG_E;
        break;
    case '~':
        option_mask32 ^= FLAG_TILDE;
        break;
#if ENABLE_FEATURE_LESS_TRUNCATE
    case 'S':
        option_mask32 ^= FLAG_S;
        buffer_fill_and_print();
        break;
#endif
#if ENABLE_FEATURE_LESS_LINENUMS
    case 'N':
        option_mask32 ^= FLAG_N;
        re_wrap();
        buffer_fill_and_print();
        break;
#endif
    }
}

#ifdef BLOAT
static void show_flag_status(void)
{
    int keypress;
    int flag_val;

    clear_line();
    bb_putchar('_');
    keypress = less_getch(1);

    switch (keypress) {
    case 'M':
        flag_val = option_mask32 & FLAG_M;
        break;
    case 'm':
        flag_val = option_mask32 & FLAG_m;
        break;
    case '~':
        flag_val = option_mask32 & FLAG_TILDE;
        break;
    case 'N':
        flag_val = option_mask32 & FLAG_N;
        break;
    case 'E':
        flag_val = option_mask32 & FLAG_E;
        break;
    default:
        flag_val = 0;
        break;
    }

    clear_line();
    printf(HIGHLIGHT"The status of the flag is: %u"NORMAL, flag_val != 0);
}
#endif

#endif /* ENABLE_FEATURE_LESS_DASHCMD */

static void save_input_to_file(void)
{
    const char *msg = "";
    char *current_line;
    unsigned i;
    FILE *fp;

    print_statusline("Log file: ");
    current_line = less_gets(sizeof("Log file: ")-1);
    if (current_line[0]) {
        fp = fopen_for_write(current_line);
        if (!fp) {
            msg = "Error opening log file";
            goto ret;
        }
        for (i = 0; i <= max_fline; i++)
            fprintf(fp, "%s\n", flines[i]);
        fclose(fp);
        msg = "Done";
    }
 ret:
    print_statusline(msg);
    free(current_line);
}

#if ENABLE_FEATURE_LESS_MARKS
static void add_mark(void)
{
    int letter;

    print_statusline("Mark: ");
    letter = less_getch(sizeof("Mark: ") - 1);

    if (isalpha(letter)) {
        /* If we exceed 15 marks, start overwriting previous ones */
        if (num_marks == 14)
            num_marks = 0;

        mark_lines[num_marks][0] = letter;
        mark_lines[num_marks][1] = cur_fline;
        num_marks++;
    } else {
        print_statusline("Invalid mark letter");
    }
}

static void goto_mark(void)
{
    int letter;
    int i;

    print_statusline("Go to mark: ");
    letter = less_getch(sizeof("Go to mark: ") - 1);
    clear_line();

    if (isalpha(letter)) {
        for (i = 0; i <= num_marks; i++)
            if (letter == mark_lines[i][0]) {
                buffer_line(mark_lines[i][1]);
                break;
            }
        if (num_marks == 14 && letter != mark_lines[14][0])
            print_statusline("Mark not set");
    } else
        print_statusline("Invalid mark letter");
}
#endif

#if ENABLE_FEATURE_LESS_BRACKETS
static char opp_bracket(char bracket)
{
    switch (bracket) {
        case '{': case '[': /* '}' == '{' + 2. Same for '[' */
            bracket++;
        case '(':           /* ')' == '(' + 1 */
            bracket++;
            break;
        case '}': case ']':
            bracket--;
        case ')':
            bracket--;
            break;
    };
    return bracket;
}

static void match_right_bracket(char bracket)
{
    unsigned i;

    if (strchr(flines[cur_fline], bracket) == NULL) {
        print_statusline("No bracket in top line");
        return;
    }
    bracket = opp_bracket(bracket);
    for (i = cur_fline + 1; i < max_fline; i++) {
        if (strchr(flines[i], bracket) != NULL) {
            buffer_line(i);
            return;
        }
    }
    print_statusline("No matching bracket found");
}

static void match_left_bracket(char bracket)
{
    int i;

    if (strchr(flines[cur_fline + max_displayed_line], bracket) == NULL) {
        print_statusline("No bracket in bottom line");
        return;
    }

    bracket = opp_bracket(bracket);
    for (i = cur_fline + max_displayed_line; i >= 0; i--) {
        if (strchr(flines[i], bracket) != NULL) {
            buffer_line(i);
            return;
        }
    }
    print_statusline("No matching bracket found");
}
#endif  /* FEATURE_LESS_BRACKETS */

static void keypress_process(int keypress)
{
    switch (keypress) {
    case KEYCODE_DOWN: case 'e': case 'j': case 0x0d:
        buffer_down(1);
        break;
    case KEYCODE_UP: case 'y': case 'k':
        buffer_up(1);
        break;
    case KEYCODE_PAGEDOWN: case ' ': case 'z': case 'f':
        buffer_down(max_displayed_line + 1);
        break;
    case KEYCODE_PAGEUP: case 'w': case 'b':
        buffer_up(max_displayed_line + 1);
        break;
    case 'd':
        buffer_down((max_displayed_line + 1) / 2);
        break;
    case 'u':
        buffer_up((max_displayed_line + 1) / 2);
        break;
    case KEYCODE_HOME: case 'g': case 'p': case '<': case '%':
        buffer_line(0);
        break;
    case KEYCODE_END: case 'G': case '>':
        cur_fline = MAXLINES;
        read_lines();
        buffer_line(cur_fline);
        break;
    case 'q': case 'Q':
        less_exit(EXIT_SUCCESS);
        break;
#if ENABLE_FEATURE_LESS_MARKS
    case 'm':
        add_mark();
        buffer_print();
        break;
    case '\'':
        goto_mark();
        buffer_print();
        break;
#endif
    case 'r': case 'R':
        /* TODO: (1) also bind ^R, ^L to this?
         * (2) re-measure window size?
         */
        buffer_print();
        break;
    /*case 'R':
        full_repaint();
        break;*/
    case 's':
        save_input_to_file();
        break;
    case 'E':
        examine_file();
        break;
#if ENABLE_FEATURE_LESS_FLAGS
    case '=':
        m_status_print();
        break;
#endif
#if ENABLE_FEATURE_LESS_REGEXP
    case '/':
        option_mask32 &= ~LESS_STATE_MATCH_BACKWARDS;
        regex_process();
        break;
    case 'n':
        goto_match(match_pos + 1);
        break;
    case 'N':
        goto_match(match_pos - 1);
        break;
    case '?':
        option_mask32 |= LESS_STATE_MATCH_BACKWARDS;
        regex_process();
        break;
#endif
#if ENABLE_FEATURE_LESS_DASHCMD
    case '-':
        flag_change();
        buffer_print();
        break;
#ifdef BLOAT
    case '_':
        show_flag_status();
        break;
#endif
#endif
#if ENABLE_FEATURE_LESS_BRACKETS
    case '{': case '(': case '[':
        match_right_bracket(keypress);
        break;
    case '}': case ')': case ']':
        match_left_bracket(keypress);
        break;
#endif
    case ':':
        colon_process();
        break;
    }

    if (isdigit(keypress))
        number_process(keypress);
}

static void sig_catcher(int sig)
{
    less_exit(- sig);
}

#if ENABLE_FEATURE_LESS_WINCH
static void sigwinch_handler(int sig UNUSED_PARAM)
{
    winch_counter++;
}
#endif

int less_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int less_main(int argc, char **argv)
{
    char *tty_name;
    int tty_fd;

    INIT_G();

    /* TODO: -x: do not interpret backspace, -xx: tab also
     * -xxx: newline also
     * -w N: assume width N (-xxx -w 32: hex viewer of sorts)
     * -s: condense many empty lines to one
     *     (used by some setups for manpage display)
     */
    getopt32(argv, "EMmN~I" IF_FEATURE_LESS_TRUNCATE("S") /*ignored:*/"s");
    argc -= optind;
    argv += optind;
    num_files = argc;
    files = argv;

    /* Another popular pager, most, detects when stdout
     * is not a tty and turns into cat. This makes sense. */
    if (!isatty(STDOUT_FILENO))
        return bb_cat(argv);

    if (!num_files) {
        if (isatty(STDIN_FILENO)) {
            /* Just "less"? No args and no redirection? */
            bb_error_msg("missing filename");
            bb_show_usage();
        }
    } else {
        filename = xstrdup(files[0]);
    }

    if (option_mask32 & FLAG_TILDE)
        empty_line_marker = "";

    /* Some versions of less can survive w/o controlling tty,
     * try to do the same. This also allows to specify an alternative
     * tty via "less 1<>TTY".
     * We don't try to use STDOUT_FILENO directly,
     * since we want to set this fd to non-blocking mode,
     * and not bother with restoring it on exit.
     */
    tty_name = xmalloc_ttyname(STDOUT_FILENO);
    if (tty_name) {
        tty_fd = open(tty_name, O_RDONLY);
        free(tty_name);
        if (tty_fd < 0)
            goto try_ctty;
    } else {
        /* Try controlling tty */
 try_ctty:
        tty_fd = open(CURRENT_TTY, O_RDONLY);
        if (tty_fd < 0)
            return bb_cat(argv);
    }
    ndelay_on(tty_fd);
    kbd_fd = tty_fd; /* save in a global */

    tcgetattr(kbd_fd, &term_orig);
    term_less = term_orig;
    term_less.c_lflag &= ~(ICANON | ECHO);
    term_less.c_iflag &= ~(IXON | ICRNL);
    /*term_less.c_oflag &= ~ONLCR;*/
    term_less.c_cc[VMIN] = 1;
    term_less.c_cc[VTIME] = 0;

    IF_FEATURE_LESS_ASK_TERMINAL(G.winsize_err =) get_terminal_width_height(kbd_fd, &width, &max_displayed_line);
    /* 20: two tabstops + 4 */
    if (width < 20 || max_displayed_line < 3)
        return bb_cat(argv);
    max_displayed_line -= 2;

    /* We want to restore term_orig on exit */
    bb_signals(BB_FATAL_SIGS, sig_catcher);
#if ENABLE_FEATURE_LESS_WINCH
    signal(SIGWINCH, sigwinch_handler);
#endif

    buffer = xmalloc((max_displayed_line+1) * sizeof(char *));
    reinitialize();
    while (1) {
        int64_t keypress;

#if ENABLE_FEATURE_LESS_WINCH
        while (WINCH_COUNTER) {
 again:
            winch_counter--;
            IF_FEATURE_LESS_ASK_TERMINAL(G.winsize_err =) get_terminal_width_height(kbd_fd, &width, &max_displayed_line);
 IF_FEATURE_LESS_ASK_TERMINAL(got_size:)
            /* 20: two tabstops + 4 */
            if (width < 20)
                width = 20;
            if (max_displayed_line < 3)
                max_displayed_line = 3;
            max_displayed_line -= 2;
            free(buffer);
            buffer = xmalloc((max_displayed_line+1) * sizeof(char *));
            /* Avoid re-wrap and/or redraw if we already know
             * we need to do it again. These ops are expensive */
            if (WINCH_COUNTER)
                goto again;
            re_wrap();
            if (WINCH_COUNTER)
                goto again;
            buffer_fill_and_print();
            /* This took some time. Loop back and check,
             * were there another SIGWINCH? */
        }
        keypress = less_getch(-1); /* -1: do not position cursor */
# if ENABLE_FEATURE_LESS_ASK_TERMINAL
        if ((int32_t)keypress == KEYCODE_CURSOR_POS) {
            uint32_t rc = (keypress >> 32);
            width = (rc & 0x7fff);
            max_displayed_line = ((rc >> 16) & 0x7fff);
            goto got_size;
        }
# endif
#else
        keypress = less_getch(-1); /* -1: do not position cursor */
#endif
        keypress_process(keypress);
    }
}

/*
Help text of less version 418 is below.
If you are implementing something, keeping
key and/or command line switch compatibility is a good idea:


                   SUMMARY OF LESS COMMANDS

      Commands marked with * may be preceded by a number, N.
      Notes in parentheses indicate the behavior if N is given.
  h  H                 Display this help.
  q  :q  Q  :Q  ZZ     Exit.
 ---------------------------------------------------------------------------
                           MOVING
  e  ^E  j  ^N  CR  *  Forward  one line   (or N lines).
  y  ^Y  k  ^K  ^P  *  Backward one line   (or N lines).
  f  ^F  ^V  SPACE  *  Forward  one window (or N lines).
  b  ^B  ESC-v      *  Backward one window (or N lines).
  z                 *  Forward  one window (and set window to N).
  w                 *  Backward one window (and set window to N).
  ESC-SPACE         *  Forward  one window, but don't stop at end-of-file.
  d  ^D             *  Forward  one half-window (and set half-window to N).
  u  ^U             *  Backward one half-window (and set half-window to N).
  ESC-)  RightArrow *  Left  one half screen width (or N positions).
  ESC-(  LeftArrow  *  Right one half screen width (or N positions).
  F                    Forward forever; like "tail -f".
  r  ^R  ^L            Repaint screen.
  R                    Repaint screen, discarding buffered input.
        ---------------------------------------------------
        Default "window" is the screen height.
        Default "half-window" is half of the screen height.
 ---------------------------------------------------------------------------
                          SEARCHING
  /pattern          *  Search forward for (N-th) matching line.
  ?pattern          *  Search backward for (N-th) matching line.
  n                 *  Repeat previous search (for N-th occurrence).
  N                 *  Repeat previous search in reverse direction.
  ESC-n             *  Repeat previous search, spanning files.
  ESC-N             *  Repeat previous search, reverse dir. & spanning files.
  ESC-u                Undo (toggle) search highlighting.
        ---------------------------------------------------
        Search patterns may be modified by one or more of:
        ^N or !  Search for NON-matching lines.
        ^E or *  Search multiple files (pass thru END OF FILE).
        ^F or @  Start search at FIRST file (for /) or last file (for ?).
        ^K       Highlight matches, but don't move (KEEP position).
        ^R       Don't use REGULAR EXPRESSIONS.
 ---------------------------------------------------------------------------
                           JUMPING
  g  <  ESC-<       *  Go to first line in file (or line N).
  G  >  ESC->       *  Go to last line in file (or line N).
  p  %              *  Go to beginning of file (or N percent into file).
  t                 *  Go to the (N-th) next tag.
  T                 *  Go to the (N-th) previous tag.
  {  (  [           *  Find close bracket } ) ].
  }  )  ]           *  Find open bracket { ( [.
  ESC-^F <c1> <c2>  *  Find close bracket <c2>.
  ESC-^B <c1> <c2>  *  Find open bracket <c1>
        ---------------------------------------------------
        Each "find close bracket" command goes forward to the close bracket
          matching the (N-th) open bracket in the top line.
        Each "find open bracket" command goes backward to the open bracket
          matching the (N-th) close bracket in the bottom line.
  m<letter>            Mark the current position with <letter>.
  '<letter>            Go to a previously marked position.
  ''                   Go to the previous position.
  ^X^X                 Same as '.
        ---------------------------------------------------
        A mark is any upper-case or lower-case letter.
        Certain marks are predefined:
             ^  means  beginning of the file
             $  means  end of the file
 ---------------------------------------------------------------------------
                        CHANGING FILES
  :e [file]            Examine a new file.
  ^X^V                 Same as :e.
  :n                *  Examine the (N-th) next file from the command line.
  :p                *  Examine the (N-th) previous file from the command line.
  :x                *  Examine the first (or N-th) file from the command line.
  :d                   Delete the current file from the command line list.
  =  ^G  :f            Print current file name.
 ---------------------------------------------------------------------------
                    MISCELLANEOUS COMMANDS
  -<flag>              Toggle a command line option [see OPTIONS below].
  --<name>             Toggle a command line option, by name.
  _<flag>              Display the setting of a command line option.
  __<name>             Display the setting of an option, by name.
  +cmd                 Execute the less cmd each time a new file is examined.
  !command             Execute the shell command with $SHELL.
  |Xcommand            Pipe file between current pos & mark X to shell command.
  v                    Edit the current file with $VISUAL or $EDITOR.
  V                    Print version number of "less".
 ---------------------------------------------------------------------------
                           OPTIONS
        Most options may be changed either on the command line,
        or from within less by using the - or -- command.
        Options may be given in one of two forms: either a single
        character preceded by a -, or a name preceded by --.
  -?  ........  --help
                  Display help (from command line).
  -a  ........  --search-skip-screen
                  Forward search skips current screen.
  -b [N]  ....  --buffers=[N]
                  Number of buffers.
  -B  ........  --auto-buffers
                  Don't automatically allocate buffers for pipes.
  -c  ........  --clear-screen
                  Repaint by clearing rather than scrolling.
  -d  ........  --dumb
                  Dumb terminal.
  -D [xn.n]  .  --color=xn.n
                  Set screen colors. (MS-DOS only)
  -e  -E  ....  --quit-at-eof  --QUIT-AT-EOF
                  Quit at end of file.
  -f  ........  --force
                  Force open non-regular files.
  -F  ........  --quit-if-one-screen
                  Quit if entire file fits on first screen.
  -g  ........  --hilite-search
                  Highlight only last match for searches.
  -G  ........  --HILITE-SEARCH
                  Don't highlight any matches for searches.
  -h [N]  ....  --max-back-scroll=[N]
                  Backward scroll limit.
  -i  ........  --ignore-case
                  Ignore case in searches that do not contain uppercase.
  -I  ........  --IGNORE-CASE
                  Ignore case in all searches.
  -j [N]  ....  --jump-target=[N]
                  Screen position of target lines.
  -J  ........  --status-column
                  Display a status column at left edge of screen.
  -k [file]  .  --lesskey-file=[file]
                  Use a lesskey file.
  -L  ........  --no-lessopen
                  Ignore the LESSOPEN environment variable.
  -m  -M  ....  --long-prompt  --LONG-PROMPT
                  Set prompt style.
  -n  -N  ....  --line-numbers  --LINE-NUMBERS
                  Don't use line numbers.
  -o [file]  .  --log-file=[file]
                  Copy to log file (standard input only).
  -O [file]  .  --LOG-FILE=[file]
                  Copy to log file (unconditionally overwrite).
  -p [pattern]  --pattern=[pattern]
                  Start at pattern (from command line).
  -P [prompt]   --prompt=[prompt]
                  Define new prompt.
  -q  -Q  ....  --quiet  --QUIET  --silent --SILENT
                  Quiet the terminal bell.
  -r  -R  ....  --raw-control-chars  --RAW-CONTROL-CHARS
                  Output "raw" control characters.
  -s  ........  --squeeze-blank-lines
                  Squeeze multiple blank lines.
  -S  ........  --chop-long-lines
                  Chop long lines.
  -t [tag]  ..  --tag=[tag]
                  Find a tag.
  -T [tagsfile] --tag-file=[tagsfile]
                  Use an alternate tags file.
  -u  -U  ....  --underline-special  --UNDERLINE-SPECIAL
                  Change handling of backspaces.
  -V  ........  --version
                  Display the version number of "less".
  -w  ........  --hilite-unread
                  Highlight first new line after forward-screen.
  -W  ........  --HILITE-UNREAD
                  Highlight first new line after any forward movement.
  -x [N[,...]]  --tabs=[N[,...]]
                  Set tab stops.
  -X  ........  --no-init
                  Don't use termcap init/deinit strings.
                --no-keypad
                  Don't use termcap keypad init/deinit strings.
  -y [N]  ....  --max-forw-scroll=[N]
                  Forward scroll limit.
  -z [N]  ....  --window=[N]
                  Set size of window.
  -" [c[c]]  .  --quotes=[c[c]]
                  Set shell quote characters.
  -~  ........  --tilde
                  Don't display tildes after end of file.
  -# [N]  ....  --shift=[N]
                  Horizontal scroll amount (0 = one half screen width)

 ---------------------------------------------------------------------------
                          LINE EDITING
        These keys can be used to edit text being entered
        on the "command line" at the bottom of the screen.
 RightArrow                       ESC-l     Move cursor right one character.
 LeftArrow                        ESC-h     Move cursor left one character.
 CNTL-RightArrow  ESC-RightArrow  ESC-w     Move cursor right one word.
 CNTL-LeftArrow   ESC-LeftArrow   ESC-b     Move cursor left one word.
 HOME                             ESC-0     Move cursor to start of line.
 END                              ESC-$     Move cursor to end of line.
 BACKSPACE                                  Delete char to left of cursor.
 DELETE                           ESC-x     Delete char under cursor.
 CNTL-BACKSPACE   ESC-BACKSPACE             Delete word to left of cursor.
 CNTL-DELETE      ESC-DELETE      ESC-X     Delete word under cursor.
 CNTL-U           ESC (MS-DOS only)         Delete entire line.
 UpArrow                          ESC-k     Retrieve previous command line.
 DownArrow                        ESC-j     Retrieve next command line.
 TAB                                        Complete filename & cycle.
 SHIFT-TAB                        ESC-TAB   Complete filename & reverse cycle.
 CNTL-L                                     Complete filename, list all.
*/