busybox.1.0 lash 运行流程分析

程序运行流程：

lash_main -> busy_loop -> get_command ->    (ash.c)
cmdedit_read_input    (cmdedit.c)

cmdedit_read_input：

int cmdedit_read_input(char *prompt, char command[BUFSIZ])
{

    int break_out = 0;
    int lastWasTab = FALSE;
    unsigned char c = 0;

    /* prepare before init handlers */
    cmdedit_y = 0; /* quasireal y, not true work if line > xt*yt */
    len = 0;
    command_ps = command;

    getTermSettings(0, (void *) &initial_settings);
    memcpy(&new_settings, &initial_settings, sizeof(struct termios));
    new_settings.c_lflag &= ~ICANON; /* unbuffered input */
    /* Turn off echoing and CTRL-C, so we can trap it */
    new_settings.c_lflag &= ~(ECHO | ECHONL | ISIG);
    /* Hmm, in linux c_cc[] not parsed if set ~ICANON */
    new_settings.c_cc[VMIN] = 1;
    new_settings.c_cc[VTIME] = 0;
    /* Turn off CTRL-C, so we can trap it */
#       ifndef _POSIX_VDISABLE
#               define _POSIX_VDISABLE '\0'
#       endif
    new_settings.c_cc[VINTR] = _POSIX_VDISABLE;
    command[0] = 0;

    setTermSettings(0, (void *) &new_settings);
    handlers_sets |= SET_RESET_TERM;

    /* Now initialize things */
    cmdedit_init();
    /* Print out the command prompt */
    parse_prompt(prompt);

    while (1) {

        fflush(stdout); /* buffered out to fast */

        if (safe_read(0, &c, 1) < 1)
            /* if we can't read input then exit */
            goto prepare_to_die;

        switch (c) {
        case '\n':
        case '\r':
            /* Enter */
            goto_new_line();
            break_out = 1;
            break;
        case 1:
            /* Control-a -- Beginning of line */
            input_backward(cursor);
            break;
        case 2:
            /* Control-b -- Move back one character */
            input_backward(1);
            break;
        case 3:
            /* Control-c -- stop gathering input */
            goto_new_line();
#ifndef CONFIG_ASH
            command[0] = 0;
            len = 0;
            lastWasTab = FALSE;
            put_prompt();
#else
            len = 0;
            break_out = -1; /* to control traps */
#endif
            break;
        case 4:
            /* Control-d -- Delete one character, or exit
             * if the len=0 and no chars to delete */
            if (len == 0) {
                    errno = 0;
prepare_to_die:
#if !defined(CONFIG_ASH)
                printf("exit");
                goto_new_line();
                /* cmdedit_reset_term() called in atexit */
                exit(EXIT_SUCCESS);
#else
                /* to control stopped jobs */
                len = break_out = -1;
                break;
#endif
            } else {
                input_delete();
            }
            break;
        case 5:
            /* Control-e -- End of line */
            input_end();
            break;
        case 6:
            /* Control-f -- Move forward one character */
            input_forward();
            break;
        case '\b':
        case DEL:
            /* Control-h and DEL */
            input_backspace();
            break;
        case '\t':
#ifdef CONFIG_FEATURE_COMMAND_TAB_COMPLETION
            input_tab(&lastWasTab);
#endif
            break;
        case 11:
            /* Control-k -- clear to end of line */
            *(command + cursor) = 0;
            len = cursor;
            printf("\033[J");
            break;
        case 12:
            /* Control-l -- clear screen */
            printf("\033[H");
            redraw(0, len-cursor);
            break;
#if MAX_HISTORY >= 1
        case 14:
            /* Control-n -- Get next command in history */
            if (get_next_history())
                goto rewrite_line;
            break;
        case 16:
            /* Control-p -- Get previous command from history */
            if (cur_history > 0) {
                get_previous_history();
                goto rewrite_line;
            } else {
                beep();
            }
            break;
#endif
        case 21:
            /* Control-U -- Clear line before cursor */
            if (cursor) {
                strcpy(command, command + cursor);
                redraw(cmdedit_y, len -= cursor);
            }
            break;
        case 23:
            /* Control-W -- Remove the last word */
            while (cursor > 0 && isspace(command[cursor-1]))
                input_backspace();
            while (cursor > 0 &&!isspace(command[cursor-1]))
                input_backspace();
            break;
        case ESC:{
            /* escape sequence follows */
            if (safe_read(0, &c, 1) < 1)
                goto prepare_to_die;
            /* different vt100 emulations */
            if (c == '[' || c == 'O') {
                if (safe_read(0, &c, 1) < 1)
                    goto prepare_to_die;
            }
            if (c >= '1' && c <= '9') {
                unsigned char dummy;

                if (safe_read(0, &dummy, 1) < 1)
                    goto prepare_to_die;
                if(dummy != '~')
                    c = 0;
            }
            switch (c) {
#ifdef CONFIG_FEATURE_COMMAND_TAB_COMPLETION
            case '\t': /* Alt-Tab */

                input_tab(&lastWasTab);
                break;
#endif
#if MAX_HISTORY >= 1
            case 'A':
                /* Up Arrow -- Get previous command from history */
                if (cur_history > 0) {
                    get_previous_history();
                    goto rewrite_line;
                } else {
                    beep();
                }
                break;
            case 'B':
                /* Down Arrow -- Get next command in history */
                if (!get_next_history())
                break;
                /* Rewrite the line with the selected history item */
rewrite_line:
                /* change command */
                len = strlen(strcpy(command, history[cur_history]));
                /* redraw and go to end line */
                redraw(cmdedit_y, 0);
                break;
#endif
            case 'C':
                /* Right Arrow -- Move forward one character */
                input_forward();
                break;
            case 'D':
                /* Left Arrow -- Move back one character */
                input_backward(1);
                break;
            case '3':
                /* Delete */
                input_delete();
                break;
            case '1':
            case 'H':
                /* <Home> */
                input_backward(cursor);
                break;
            case '4':
            case 'F':
                /* <End> */
                input_end();
                break;
            default:
                c = 0;
                beep();
            }
            break;
        }

        default: /* If it's regular input, do the normal thing */
#ifdef CONFIG_FEATURE_NONPRINTABLE_INVERSE_PUT
            /* Control-V -- Add non-printable symbol */
            if (c == 22) {
                if (safe_read(0, &c, 1) < 1)
                    goto prepare_to_die;
                if (c == 0) {
                    beep();
                    break;
                }
            } else
#endif
            if (!Isprint(c)) /* Skip non-printable characters */
                break;

            if (len >= (BUFSIZ - 2)) /* Need to leave space for enter */
                break;

            len++;

            if (cursor == (len - 1)) { /* Append if at the end of the line */
                *(command + cursor) = c;
                *(command + cursor + 1) = 0;
                cmdedit_set_out_char(0);
            } else { /* Insert otherwise */
                int sc = cursor;

                memmove(command + sc + 1, command + sc, len - sc);
                *(command + sc) = c;
                sc++;
                /* rewrite from cursor */
                input_end();
                /* to prev x pos + 1 */
                input_backward(cursor - sc);
            }
            break;