Subversion Repositories SvarDOS

/* This file is part of the SvarCOM project and is published under the terms

 * of the MIT license.

 *

 * Copyright (C) 2021 Mateusz Viste

 *

 * Permission is hereby granted, free of charge, to any person obtaining a

 * copy of this software and associated documentation files (the "Software"),

 * to deal in the Software without restriction, including without limitation

 * the rights to use, copy, modify, merge, publish, distribute, sublicense,

 * and/or sell copies of the Software, and to permit persons to whom the

 * Software is furnished to do so, subject to the following conditions:

 *

 * The above copyright notice and this permission notice shall be included in

 * all copies or substantial portions of the Software.

 *

 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE

 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING

 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER

 * DEALINGS IN THE SOFTWARE.

 */

/*

 * SvarCOM is a command-line interpreter.

 *

 * a little memory area is allocated as high as possible. it contains:

 *  - a signature (like XMS drivers do)

 *  - a routine for exec'ing programs

 *  - a "last command" buffer for input history

 *

 * when svarcom starts, it tries locating the routine in memory.

 *

 * if found:

 *   waits for user input and processes it. if execing something is required, set the "next exec" field in routine's memory and quit.

 *

 * if not found:

 *   installs it by creating a new PSP, set int 22 vector to the routine, set my "parent PSP" to the routine

 *   and quit.

 *

 * PSP structure

 * http://www.piclist.com/techref/dos/psps.htm

 *

 *

 *

 * === MCB ===

 *

 * each time that DOS allocates memory, it prefixes the allocated memory with

 * a 16-bytes structure called a "Memory Control Block" (MCB). This control

 * block has the following structure:

 *

 * Offset  Size     Description

 *   00h   byte     'M' =  non-last member of the MCB chain

 *                  'Z' = indicates last entry in MCB chain

 *                  other values cause "Memory Allocation Failure" on exit

 *   01h   word     PSP segment address of the owner (Process Id)

 *                  possible values:

 *                    0 = free

 *                    8 = Allocated by DOS before first user pgm loaded

 *                    other = Process Id/PSP segment address of owner

 *   03h  word      number of paragraphs related to this MCB (excluding MCB)

 *   05h  11 bytes  reserved

 *   10h  ...       start of actual allocated memory block

 */

#include <i86.h>

#include <dos.h>

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <process.h>

#include "cmd.h"

#include "env.h"

#include "helpers.h"

#include "redir.h"

#include "rmodinit.h"

#include "sayonara.h"

#include "rmodcore.h" /* rmod binary inside a BUFFER array */

struct config {

  unsigned char flags; /* command.com flags, as defined in rmodinit.h */

  char *execcmd;

  unsigned short envsiz;

};

/* max length of the cmdline storage (bytes) - includes also max length of

 * line loaded from a BAT file (no more than 255 bytes!) */

#define CMDLINE_MAXLEN 255

/* sets guard values at a few places in memory for later detection of

 * overflows via memguard_check() */

static void memguard_set(void) {

  BUFFER[sizeof(BUFFER) - 1] = 0xC7;

  BUFFER[sizeof(BUFFER) - (CMDLINE_MAXLEN + 3)] = 0xC7;

}

/* checks for valguards at specific memory locations, returns 0 on success */

static int memguard_check(unsigned short rmodseg) {

  /* check RMOD signature (would be overwritten in case of stack overflow */

  static char msg[] = "!! MEMORY CORRUPTION ## DETECTED !!";

  unsigned short far *rmodsig = MK_FP(rmodseg, 0x100 + 6);

  if (*rmodsig != 0x2019) {

    msg[22] = '1';

    outputnl(msg);

    printf("rmodseg = %04X ; *rmodsig = %04X\r\n", rmodseg, *rmodsig);

    return(1);

  }

  /* check last BUFFER byte (could be overwritten by cmdline) */

  if (BUFFER[sizeof(BUFFER) - 1] != 0xC7) {

    msg[22] = '2';

    outputnl(msg);

    return(2);

  }

  /* check that cmdline BUFFER's end hasn't been touched by something else */

  if (BUFFER[sizeof(BUFFER) - (CMDLINE_MAXLEN + 3)] != 0xC7) {

    msg[22] = '3';

    outputnl(msg);

    return(3);

  }

  /* all good */

  return(0);

}

/* parses command line the hard way (directly from PSP) */

static void parse_argv(struct config *cfg) {

  unsigned short i;

  const unsigned char *cmdlinelen = (unsigned char *)0x80;

  char *cmdline = (char *)0x81;

  memset(cfg, 0, sizeof(*cfg));

  /* set a NULL terminator on cmdline */

  cmdline[*cmdlinelen] = 0;

  for (i = 0;;) {

    /* skip over any leading spaces */

    for (;; i++) {

      if (cmdline[i] == 0) return;

      if (cmdline[i] != ' ') break;

    }

    if (cmdline[i] != '/') {

      output("Invalid parameter: ");

      outputnl(cmdline + i);

      /* exit(1); */

    } else {

      i++;        /* skip the slash */

      switch (cmdline[i]) {

        case 'c': /* /C = execute command and quit */

        case 'C':

          cfg->flags |= FLAG_EXEC_AND_QUIT;

          /* FALLTHRU */

        case 'k': /* /K = execute command and keep running */

        case 'K':

          cfg->execcmd = cmdline + i + 1;

          return;

        case 'e': /* preset the initial size of the environment block */

        case 'E':

          i++;

          if (cmdline[i] == ':') i++; /* could be /E:size */

          atous(&(cfg->envsiz), cmdline + i);

          if (cfg->envsiz < 64) cfg->envsiz = 0;

          break;

        case 'p': /* permanent shell (can't exit + run autoexec.bat) */

        case 'P':

          cfg->flags |= FLAG_PERMANENT;

          break;

        case '?':

          outputnl("Starts the SvarCOM command interpreter");

          outputnl("");

          outputnl("COMMAND /E:nnn [/[C|K] command]");

          outputnl("");

          outputnl("/E:nnn     Sets the environment size to nnn bytes");

          outputnl("/P         Makes the new command interpreter permanent (can't exit)");

          outputnl("/C         Executes the specified command and returns");

          outputnl("/K         Executes the specified command and continues running");

          exit(1);

          break;

        default:

          output("Invalid switch:");

          output(" ");

          outputnl(cmdline + i);

          exit(1);

          break;

      }

    }

    /* move to next argument or quit processing if end of cmdline */

    for (i++; (cmdline[i] != 0) && (cmdline[i] != ' ') && (cmdline[i] != '/'); i++);

  }

}

/* builds the prompt string and displays it. buff is filled with a zero-terminated copy of the prompt. */

static void build_and_display_prompt(char *buff, unsigned short envseg) {

  char *s = buff;

  /* locate the prompt variable or use the default pattern */

  const char far *fmt = env_lookup_val(envseg, "PROMPT");

  if ((fmt == NULL) || (*fmt == 0)) fmt = "$p$g"; /* fallback to default if empty */

  /* build the prompt string based on pattern */

  for (; *fmt != 0; fmt++) {

    if (*fmt != '$') {

      *s = *fmt;

      s++;

      continue;

    }

    /* escape code ($P, etc) */

    fmt++;

    switch (*fmt) {

      case 'Q':  /* $Q = = (equal sign) */

      case 'q':

        *s = '=';

        s++;

        break;

      case '$':  /* $$ = $ (dollar sign) */

        *s = '$';

        s++;

        break;

      case 'T':  /* $t = current time */

      case 't':

        s += sprintf(s, "00:00"); /* TODO */

        break;

      case 'D':  /* $D = current date */

      case 'd':

        s += sprintf(s, "1985-07-29"); /* TODO */

        break;

      case 'P':  /* $P = current drive and path */

      case 'p':

        _asm {

          mov ah, 0x19    /* DOS 1+ - GET CURRENT DRIVE */

          int 0x21

          mov bx, s

          mov [bx], al  /* AL = drive (00 = A:, 01 = B:, etc */

        }

        *s += 'A';

        s++;

        *s = ':';

        s++;

        *s = '\\';

        s++;

        _asm {

          mov ah, 0x47    /* DOS 2+ - CWD - GET CURRENT DIRECTORY */

          xor dl,dl       /* DL = drive number (00h = default, 01h = A:, etc) */

          mov si, s       /* DS:SI -> 64-byte buffer for ASCIZ pathname */

          int 0x21

        }

        while (*s != 0) s++; /* move ptr forward to end of pathname */

        break;

      case 'V':  /* $V = DOS version number */

      case 'v':

        s += sprintf(s, "VER"); /* TODO */

        break;

      case 'N':  /* $N = current drive */

      case 'n':

        _asm {

          mov ah, 0x19    /* DOS 1+ - GET CURRENT DRIVE */

          int 0x21

          mov bx, s

          mov [bx], al  /* AL = drive (00 = A:, 01 = B:, etc */

        }

        *s += 'A';

        s++;

        break;

      case 'G':  /* $G = > (greater-than sign) */

      case 'g':

        *s = '>';

        s++;

        break;

      case 'L':  /* $L = < (less-than sign) */

      case 'l':

        *s = '<';

        s++;

        break;

      case 'B':  /* $B = | (pipe) */

      case 'b':

        *s = '|';

        s++;

        break;

      case 'H':  /* $H = backspace (erases previous character) */

      case 'h':

        *s = '\b';

        s++;

        break;

      case 'E':  /* $E = Escape code (ASCII 27) */

      case 'e':

        *s = 27;

        s++;

        break;

      case '_':  /* $_ = CR+LF */

        *s = '\r';

        s++;

        *s = '\n';

        s++;

        break;

    }

  }

  *s = 0;

  output(buff);

}

/* tries locating executable fname in path and fille res with result. returns 0 on success,

 * -1 on failed match and -2 on failed match + "don't even try with other paths"

 * format is filled the offset where extension starts in fname (-1 if not found) */

int lookup_cmd(char *res, const char *fname, const char *path, const char **extptr) {

  unsigned short lastbslash = 0xffff;

  unsigned short i, len;

  unsigned char explicitpath = 0;

  /* does the original fname had an explicit path prefix or explicit ext? */

  *extptr = NULL;

  for (i = 0; fname[i] != 0; i++) {

    switch (fname[i]) {

      case ':':

      case '\\':

        explicitpath = 1;

        *extptr = NULL; /* extension is the last dot AFTER all path delimiters */

        break;

      case '.':

        *extptr = fname + i + 1;

        break;

    }

  }

  /* normalize filename */

  if (file_truename(fname, res) != 0) return(-2);

  /* printf("truename: %s\r\n", res); */

  /* figure out where the command starts and if it has an explicit extension */

  for (len = 0; res[len] != 0; len++) {

    switch (res[len]) {

      case '?':   /* abort on any wildcard character */

      case '*':

        return(-2);

      case '\\':

        lastbslash = len;

        break;

    }

  }

  /* printf("lastbslash=%u\r\n", lastbslash); */

  /* if no path prefix in fname (':' or backslash), then assemble path+filename */

  if (!explicitpath) {

    if (path != NULL) {

      i = strlen(path);

    } else {

      i = 0;

    }

    if ((i != 0) && (path[i - 1] != '\\')) i++; /* add a byte for inserting a bkslash after path */

    memmove(res + i, res + lastbslash + 1, len - lastbslash);

    if (i != 0) {

      memmove(res, path, i);

      res[i - 1] = '\\';

    }

  }

  /* if no extension was initially provided, try matching COM, EXE, BAT */

  if (*extptr == NULL) {

    const char *ext[] = {".COM", ".EXE", ".BAT", NULL};

    len = strlen(res);

    for (i = 0; ext[i] != NULL; i++) {

      strcpy(res + len, ext[i]);

      /* printf("? '%s'\r\n", res); */

      *extptr = ext[i] + 1;

      if (file_getattr(res) >= 0) return(0);

    }

  } else { /* try finding it as-is */

    /* printf("? '%s'\r\n", res); */

    if (file_getattr(res) >= 0) return(0);

  }

  /* not found */

  if (explicitpath) return(-2); /* don't bother trying other paths, the caller had its own path preset anyway */

  return(-1);

}

static void run_as_external(char *buff, const char *cmdline, unsigned short envseg, struct rmod_props far *rmod) {

  char *cmdfile = buff + 512;

  const char far *pathptr;

  int lookup;

  unsigned short i;

  const char *ext;

  char *cmd = buff + 256;

  const char *cmdtail;

  char far *rmod_execprog = MK_FP(rmod->rmodseg, RMOD_OFFSET_EXECPROG);

  char far *rmod_cmdtail = MK_FP(rmod->rmodseg, 0x81);

  _Packed struct {

    unsigned short envseg;

    unsigned long cmdtail;

    unsigned long fcb1;

    unsigned long fcb2;

  } far *ExecParam = MK_FP(rmod->rmodseg, RMOD_OFFSET_EXECPARAM);

  /* find cmd and cmdtail */

  i = 0;

  cmdtail = cmdline;

  while (*cmdtail == ' ') cmdtail++; /* skip any leading spaces */

  while ((*cmdtail != ' ') && (*cmdtail != '/') && (*cmdtail != '+') && (*cmdtail != 0)) {

    cmd[i++] = *cmdtail;

    cmdtail++;

  }

  cmd[i] = 0;

  /* is this a command in curdir? */

  lookup = lookup_cmd(cmdfile, cmd, NULL, &ext);

  if (lookup == 0) {

    /* printf("FOUND LOCAL EXEC FILE: '%s'\r\n", cmdfile); */

    goto RUNCMDFILE;

  } else if (lookup == -2) {

    /* puts("NOT FOUND"); */

    return;

  }

  /* try matching something in PATH */

  pathptr = env_lookup_val(envseg, "PATH");

  if (pathptr == NULL) return;

  /* try each path in %PATH% */

  for (;;) {

    for (i = 0;; i++) {

      buff[i] = *pathptr;

      if ((buff[i] == 0) || (buff[i] == ';')) break;

      pathptr++;

    }

    buff[i] = 0;

    lookup = lookup_cmd(cmdfile, cmd, buff, &ext);

    if (lookup == 0) break;

    if (lookup == -2) return;

    if (*pathptr == ';') {

      pathptr++;

    } else {

      return;

    }

  }

  RUNCMDFILE:

  /* special handling of batch files */

  if ((ext != NULL) && (imatch(ext, "bat"))) {

    /* copy truename of the bat file to rmod buff */

    for (i = 0; cmdfile[i] != 0; i++) rmod->batfile[i] = cmdfile[i];

    rmod->batfile[i] = 0;

    /* copy args of the bat file to rmod buff */

    for (i = 0; cmdtail[i] != 0; i++) rmod->batargs[i] = cmdtail[i];

    /* reset the 'next line to execute' counter */

    rmod->batnextline = 0;

    /* remember the echo flag (in case bat file disables echo) */

    rmod->flags &= ~FLAG_ECHO_BEFORE_BAT;

    if (rmod->flags & FLAG_ECHOFLAG) rmod->flags |= FLAG_ECHO_BEFORE_BAT;

    return;

  }

  /* copy full filename to execute */

  for (i = 0; cmdfile[i] != 0; i++) rmod_execprog[i] = cmdfile[i];

  rmod_execprog[i] = 0;

  /* copy cmdtail to rmod's PSP and compute its len */

  for (i = 0; cmdtail[i] != 0; i++) rmod_cmdtail[i] = cmdtail[i];

  rmod_cmdtail[i] = '\r';

  rmod_cmdtail[-1] = i;

  /* set up rmod to execute the command */

  ExecParam->envseg = envseg;

  ExecParam->cmdtail = (unsigned long)MK_FP(rmod->rmodseg, 0x80); /* farptr, must be in PSP format (lenbyte args \r) */

  ExecParam->fcb1 = 0; /* TODO farptr */

  ExecParam->fcb2 = 0; /* TODO farptr */

  exit(0); /* let rmod do the job now */

}

static void set_comspec_to_self(unsigned short envseg) {

  unsigned short *psp_envseg = (void *)(0x2c); /* pointer to my env segment field in the PSP */

  char far *myenv = MK_FP(*psp_envseg, 0);

  unsigned short varcount;

  char buff[256] = "COMSPEC=";

  char *buffptr = buff + 8;

  /* who am i? look into my own environment, at the end of it should be my EXEPATH string */

  while (*myenv != 0) {

    /* consume a NULL-terminated string */

    while (*myenv != 0) myenv++;

    /* move to next string */

    myenv++;

  }

  /* get next word, if 1 then EXEPATH follows */

  myenv++;

  varcount = *myenv;

  myenv++;

  varcount |= (*myenv << 8);

  myenv++;

  if (varcount != 1) return; /* NO EXEPATH FOUND */

  while (*myenv != 0) {

    *buffptr = *myenv;

    buffptr++;

    myenv++;

  }

  *buffptr = 0;

  /* printf("EXEPATH: '%s'\r\n", buff); */

  env_setvar(envseg, buff);

}

/* wait for user input */

static void cmdline_getinput(unsigned short inpseg, unsigned short inpoff) {

  _asm {

    push ax

    push bx

    push cx

    push dx

    push ds

    /* is DOSKEY support present? (INT 2Fh, AX=4800h, returns non-zero in AL if present) */

    mov ax, 0x4800

    int 0x2f

    mov bl, al /* save doskey status in BL */

    /* set up buffered input to inpseg:inpoff */

    mov ax, inpseg

    push ax

    pop ds

    mov dx, inpoff

    /* execute either DOS input or DOSKEY */

    test bl, bl /* zf set if no DOSKEY present */

    jnz DOSKEY

    mov ah, 0x0a

    int 0x21

    jmp short DONE

    DOSKEY:

    mov ax, 0x4810

    int 0x2f

    DONE:

    /* terminate command with a CR/LF */

    mov ah, 0x02 /* display character in dl */

    mov dl, 0x0d

    int 0x21

    mov dl, 0x0a

    int 0x21

    pop ds

    pop dx

    pop cx

    pop bx

    pop ax

  }

}

/* fetches a line from batch file and write it to buff (NULL-terminated),

 * increments rmod counter and returns 0 on success. */

static int getbatcmd(char *buff, unsigned char buffmaxlen, struct rmod_props far *rmod) {

  unsigned short i;

  unsigned short batname_seg = FP_SEG(rmod->batfile);

  unsigned short batname_off = FP_OFF(rmod->batfile);

  unsigned short filepos_cx = rmod->batnextline >> 16;

  unsigned short filepos_dx = rmod->batnextline & 0xffff;

  unsigned char blen = 0;

  /* open file, jump to offset filpos, and read data into buff.

   * result in blen (unchanged if EOF or failure). */

  _asm {

    push ax

    push bx

    push cx

    push dx

    /* open file (read-only) */

    mov dx, batname_off

    mov ax, batname_seg

    push ds     /* save DS */

    mov ds, ax

    mov ax, 0x3d00

    int 0x21    /* handle in ax on success */

    pop ds      /* restore DS */

    jc DONE

    mov bx, ax  /* save handle to bx */

    /* jump to file offset CX:DX */

    mov ax, 0x4200

    mov cx, filepos_cx

    mov dx, filepos_dx

    int 0x21  /* CF clear on success, DX:AX set to cur pos */

    jc CLOSEANDQUIT

    /* read the line into buff */

    mov ah, 0x3f

    xor ch, ch

    mov cl, buffmaxlen

    mov dx, buff

    int 0x21 /* CF clear on success, AX=number of bytes read */

    jc CLOSEANDQUIT

    mov blen, al

    CLOSEANDQUIT:

    /* close file (handle in bx) */

    mov ah, 0x3e

    int 0x21

    DONE:

    pop dx

    pop cx

    pop bx

    pop ax

  }

  /* printf("blen=%u filepos_cx=%u filepos_dx=%u\r\n", blen, filepos_cx, filepos_dx); */

  /* on EOF - abort processing the bat file */

  if (blen == 0) goto OOPS;

  /* find nearest \n to inc batch offset and replace \r by NULL terminator

   * I support all CR/LF, CR- and LF-terminated batch files */

  for (i = 0; i < blen; i++) {

    if ((buff[i] == '\r') || (buff[i] == '\n')) {

      if ((buff[i] == '\r') && ((i+1) < blen) && (buff[i+1] == '\n')) rmod->batnextline += 1;

      break;

    }

  }

  buff[i] = 0;

  rmod->batnextline += i + 1;

  return(0);

  OOPS:

  rmod->batfile[0] = 0;

  rmod->batnextline = 0;

  return(-1);

}

int main(void) {

  static struct config cfg;

  static unsigned short far *rmod_envseg;

  static unsigned short far *lastexitcode;

  static struct rmod_props far *rmod;

  static char *cmdline;

  rmod = rmod_find(BUFFER_len);

  if (rmod == NULL) {

    /* look at command line parameters (in case env size if set there) */

    parse_argv(&cfg);

    rmod = rmod_install(cfg.envsiz, BUFFER, BUFFER_len);

    if (rmod == NULL) {

      outputnl("ERROR: rmod_install() failed");

      return(1);

    }

    /* copy flags to rmod's storage (and enable ECHO) */

    rmod->flags = cfg.flags | FLAG_ECHOFLAG;

    /* printf("rmod installed at %Fp\r\n", rmod); */

  } else {

    /* printf("rmod found at %Fp\r\n", rmod); */

    /* if I was spawned by rmod and FLAG_EXEC_AND_QUIT is set, then I should

     * die asap, because the command has been executed already, so I no longer

     * have a purpose in life */

    if (rmod->flags & FLAG_EXEC_AND_QUIT) sayonara(rmod);

  }

  /* install a few guardvals in memory to detect some cases of overflows */

  memguard_set();

  rmod_envseg = MK_FP(rmod->rmodseg, RMOD_OFFSET_ENVSEG);

  lastexitcode = MK_FP(rmod->rmodseg, RMOD_OFFSET_LEXITCODE);

  /* make COMPSEC point to myself */

  set_comspec_to_self(*rmod_envseg);

/*  {

    unsigned short envsiz;

    unsigned short far *sizptr = MK_FP(*rmod_envseg - 1, 3);

    envsiz = *sizptr;

    envsiz *= 16;

    printf("rmod_inpbuff at %04X:%04X, env_seg at %04X:0000 (env_size = %u bytes)\r\n", rmod->rmodseg, RMOD_OFFSET_INPBUFF, *rmod_envseg, envsiz);

  }*/

  /* on /P check for the presence of AUTOEXEC.BAT and execute it if found */

  if (cfg.flags & FLAG_PERMANENT) {

    if (file_getattr("AUTOEXEC.BAT") >= 0) cfg.execcmd = "AUTOEXEC.BAT";

  }

  do {

    /* terminate previous command with a CR/LF if ECHO ON (but not during BAT processing) */

    if ((rmod->flags & FLAG_ECHOFLAG) && (rmod->batfile[0] == 0)) outputnl("");

    SKIP_NEWLINE:

    /* cancel any redirections that may have been set up before */

    redir_revert();

    /* memory check */

    memguard_check(rmod->rmodseg);

    /* preset cmdline to point at the end of my general-purpose buffer (with

     * one extra byte for the NULL terminator and another for memguard val) */

    cmdline = BUFFER + sizeof(BUFFER) - (CMDLINE_MAXLEN + 2);

    /* (re)load translation strings if needed */

    nls_langreload(BUFFER, *rmod_envseg);

    /* skip user input if I have a command to exec (/C or /K) */

    if (cfg.execcmd != NULL) {

      cmdline = cfg.execcmd;

      cfg.execcmd = NULL;

      goto EXEC_CMDLINE;

    }

    /* if batch file is being executed -> fetch next line */

    if (rmod->batfile[0] != 0) {

      if (getbatcmd(cmdline, CMDLINE_MAXLEN, rmod) != 0) { /* end of batch */

        /* restore echo flag as it was before running the bat file */

        rmod->flags &= ~FLAG_ECHOFLAG;

        if (rmod->flags & FLAG_ECHO_BEFORE_BAT) rmod->flags |= FLAG_ECHOFLAG;

        continue;

      }

      /* skip any leading spaces */

      while (*cmdline == ' ') cmdline++;

      /* output prompt and command on screen if echo on and command is not

       * inhibiting it with the @ prefix */

      if ((rmod->flags & FLAG_ECHOFLAG) && (cmdline[0] != '@')) {

        build_and_display_prompt(BUFFER, *rmod_envseg);

        outputnl(cmdline);

      }

      /* skip the @ prefix if present, it is no longer useful */

      if (cmdline[0] == '@') cmdline++;

    } else {

      /* interactive mode: display prompt (if echo enabled) and wait for user

       * command line */

      if (rmod->flags & FLAG_ECHOFLAG) build_and_display_prompt(BUFFER, *rmod_envseg);

      /* collect user input */

      cmdline_getinput(FP_SEG(rmod->inputbuf), FP_OFF(rmod->inputbuf));

      /* copy it to local cmdline */

      if (rmod->inputbuf[1] != 0) _fmemcpy(cmdline, rmod->inputbuf + 2, rmod->inputbuf[1]);

      cmdline[(unsigned)(rmod->inputbuf[1])] = 0; /* zero-terminate local buff (oriignal is '\r'-terminated) */

    }

    /* if nothing entered, loop again (but without appending an extra CR/LF) */

    if (cmdline[0] == 0) goto SKIP_NEWLINE;

    /* I jump here when I need to exec an initial command (/C or /K) */

    EXEC_CMDLINE:

    /* move pointer forward to skip over any leading spaces */

    while (*cmdline == ' ') cmdline++;

    /* update rmod's ptr to COMPSPEC so it is always up to date */

    rmod_updatecomspecptr(rmod->rmodseg, *rmod_envseg);

    /* handle redirections (if any) */

    if (redir_parsecmd(cmdline, BUFFER) != 0) {

      outputnl("");

      continue;

    }

    /* try matching (and executing) an internal command */

    if (cmd_process(rmod, *rmod_envseg, cmdline, BUFFER) >= -1) {

      /* internal command executed */

      redir_revert(); /* revert stdout (in case it was redirected) */

      continue;

    }

    /* if here, then this was not an internal command */

    run_as_external(BUFFER, cmdline, *rmod_envseg, rmod);

    /* perhaps this is a newly launched BAT file */

    if ((rmod->batfile[0] != 0) && (rmod->batnextline == 0)) goto SKIP_NEWLINE;

    /* revert stdout (so the err msg is not redirected) */

    redir_revert();

    /* run_as_external() does not return on success, if I am still alive then

     * external command failed to execute */

    outputnl("Bad command or file name");

  } while ((rmod->flags & FLAG_EXEC_AND_QUIT) == 0);

  sayonara(rmod);

  return(0);

}