path: root/nt/cmdproxy.c

/* Proxy shell designed for use with Emacs on Windows 95 and NT.
   Copyright (C) 1997, 2001-2024 Free Software Foundation, Inc.

   Accepts subset of Unix sh(1) command-line options, for compatibility
   with elisp code written for Unix.  When possible, executes external
   programs directly (a common use of /bin/sh by Emacs), otherwise
   invokes the user-specified command processor to handle built-in shell
   commands, batch files and interactive mode.

   The main function is simply to process the "-c string" option in the
   way /bin/sh does, since the standard Windows command shells use the
   convention that everything after "/c" (the Windows equivalent of
   "-c") is the input string.

This file is part of GNU Emacs.

GNU Emacs is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or (at
your option) any later version.

GNU Emacs is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */

#define DEFER_MS_W32_H
#include <config.h>

#include <windows.h>

#include <stdarg.h>  /* va_args */
#include <malloc.h>  /* alloca */
#include <stdlib.h>  /* getenv */
#include <string.h>  /* strlen */
#include <ctype.h>   /* isspace, isalpha */

/* UCRT has a C99-compatible snprintf, and _snprintf is defined inline
   in stdio.h, which we don't want to include here.  Since the
   differences in behavior between snprintf and _snprintf don't matter
   in this file, we take the easy way out.  */
#ifdef _UCRT
# define _snprintf snprintf
#endif

/* We don't want to include stdio.h because we are already duplicating
   lots of it here */
extern int _snprintf (char *buffer, size_t count, const char *format, ...);

/*******  Mock C library routines  *********************************/

/* These routines are used primarily to minimize the executable size.  */

#define stdout GetStdHandle (STD_OUTPUT_HANDLE)
#define stderr GetStdHandle (STD_ERROR_HANDLE)

#if __GNUC__ + (__GNUC_MINOR__ >= 4) >= 5
void fail (const char *, ...) __attribute__((noreturn));
#else
void fail (const char *, ...);
#endif
int vfprintf (HANDLE, const char *, va_list);
int fprintf (HANDLE, const char *, ...);
int printf (const char *, ...);
void warn (const char *, ...);

int
vfprintf (HANDLE hnd, const char * msg, va_list args)
{
  DWORD bytes_written;
  char buf[1024];

  wvsprintf (buf, msg, args);
  return WriteFile (hnd, buf, strlen (buf), &bytes_written, NULL);
}

int
fprintf (HANDLE hnd, const char * msg, ...)
{
  va_list args;
  int rc;

  va_start (args, msg);
  rc = vfprintf (hnd, msg, args);
  va_end (args);

  return rc;
}

int
printf (const char * msg, ...)
{
  va_list args;
  int rc;

  va_start (args, msg);
  rc = vfprintf (stdout, msg, args);
  va_end (args);

  return rc;
}

void
fail (const char * msg, ...)
{
  va_list args;

  va_start (args, msg);
  vfprintf (stderr, msg, args);
  va_end (args);

  exit (-1);
}

void
warn (const char * msg, ...)
{
  va_list args;

  va_start (args, msg);
  vfprintf (stderr, msg, args);
  va_end (args);
}

/******************************************************************/

static char *
canon_filename (char *fname)
{
  char *p = fname;

  while (*p)
    {
      if (*p == '/')
	*p = '\\';
      p++;
    }

  return fname;
}

static const char *
skip_space (const char *str)
{
  while (isspace (*str)) str++;
  return str;
}

static const char *
skip_nonspace (const char *str)
{
  while (*str && !isspace (*str)) str++;
  return str;
}

/* This value is never changed by the code.  We keep the code that
   supports also the value of '"', but let's allow the compiler to
   optimize it out, until someone actually uses that.  */
const int escape_char = '\\';

/* Get next token from input, advancing pointer.  */
static int
get_next_token (char * buf, const char ** pSrc)
{
  const char * p = *pSrc;
  char * o = buf;

  p = skip_space (p);
  if (*p == '"')
    {
      int escape_char_run = 0;

      /* Go through src until an ending quote is found, unescaping
	 quotes along the way.  If the escape char is not quote, then do
	 special handling of multiple escape chars preceding a quote
	 char (ie. the reverse of what Emacs does to escape quotes).  */
      p++;
      while (1)
	{
	  if (p[0] == escape_char && escape_char != '"')
	    {
	      escape_char_run++;
	      p++;
	      continue;
	    }
	  else if (p[0] == '"')
	    {
	      while (escape_char_run > 1)
		{
		  *o++ = escape_char;
		  escape_char_run -= 2;
		}

	      if (escape_char_run > 0)
		{
		  /* escaped quote */
		  *o++ = *p++;
		  escape_char_run = 0;
		}
	      else if (p[1] == escape_char && escape_char == '"')
		{
		  /* quote escaped by doubling */
		  *o++ = *p;
		  p += 2;
		}
	      else
		{
		  /* The ending quote.  */
		  *o = '\0';
		  /* Leave input pointer after token.  */
		  p++;
		  break;
		}
	    }
	  else if (p[0] == '\0')
	    {
	      /* End of string, but no ending quote found.  We might want to
		 flag this as an error, but for now will consider the end as
		 the end of the token.  */
	      if (escape_char == '\\')
		{
		  /* Output literal backslashes.  Note that if the
		     token ends with an unpaired backslash, we eat it
		     up here.  But since this case invokes undefined
		     behavior anyway, it's okay.  */
		  while (escape_char_run > 1)
		    {
		      *o++ = escape_char;
		      escape_char_run -= 2;
		    }
		}
	      *o = '\0';
	      break;
	    }
	  else
	    {
	      if (escape_char == '\\')
		{
		  /* Output literal backslashes.  Note that we don't
		     treat a backslash as an escape character here,
		     since it doesn't precede a quote.  */
		  for ( ; escape_char_run > 0; escape_char_run--)
		    *o++ = escape_char;
		}
	      *o++ = *p++;
	    }
	}
    }
  else
    {
      /* Next token is delimited by whitespace.  */
      const char * p1 = skip_nonspace (p);
      memcpy (o, p, p1 - p);
      o += (p1 - p);
      *o = '\0';
      p = p1;
    }

  *pSrc = p;

  return o - buf;
}

/* Return TRUE if PROGNAME is a batch file. */
static BOOL
batch_file_p (const char *progname)
{
  const char *exts[] = {".bat", ".cmd"};
  int n_exts = sizeof (exts) / sizeof (char *);
  int i;

  const char *ext = strrchr (progname, '.');

  if (ext)
    {
      for (i = 0; i < n_exts; i++)
        {
          if (stricmp (ext, exts[i]) == 0)
            return TRUE;
        }
    }

  return FALSE;
}

/* Search for EXEC file in DIR.  If EXEC does not have an extension,
   DIR is searched for EXEC with the standard extensions appended.  */
static int
search_dir (const char *dir, const char *exec, int bufsize, char *buffer)
{
  const char *exts[] = {".bat", ".cmd", ".exe", ".com"};
  int n_exts = sizeof (exts) / sizeof (char *);
  char *dummy;
  int i, rc;
  const char *pext = strrchr (exec, '\\');

  /* Does EXEC already include an extension?  */
  if (!pext)
    pext = exec;
  pext = strchr (pext, '.');

  /* Search the directory for the program.  */
  if (pext)
    {
      /* SearchPath will not append an extension if the file already
	 has an extension, so we must append it ourselves.  */
      char exec_ext[MAX_PATH], *p;

      p = strcpy (exec_ext, exec) + strlen (exec);

      /* Search first without any extension; if found, we are done.  */
      rc = SearchPath (dir, exec_ext, NULL, bufsize, buffer, &dummy);
      if (rc > 0)
	return rc;

      /* Try the known extensions.  */
      for (i = 0; i < n_exts; i++)
	{
	  strcpy (p, exts[i]);
	  rc = SearchPath (dir, exec_ext, NULL, bufsize, buffer, &dummy);
	  if (rc > 0)
	    return rc;
	}
    }
  else
    {
      for (i = 0; i < n_exts; i++)
	{
	  rc = SearchPath (dir, exec, exts[i], bufsize, buffer, &dummy);
	  if (rc > 0)
	    return rc;
	}
    }

  return 0;
}

/* Return the absolute name of executable file PROG, including
   any file extensions.  If an absolute name for PROG cannot be found,
   return NULL.  */
static char *
make_absolute (const char *prog)
{
  char absname[MAX_PATH];
  char dir[MAX_PATH];
  char curdir[MAX_PATH];
  char *p, *path;
  const char *fname;

  /* At least partial absolute path specified; search there.  */
  if ((isalpha (prog[0]) && prog[1] == ':') ||
      (prog[0] == '\\'))
    {
      /* Split the directory from the filename.  */
      fname = strrchr (prog, '\\');
      if (!fname)
	/* Only a drive specifier is given.  */
	fname = prog + 2;
      strncpy (dir, prog, fname - prog);
      dir[fname - prog] = '\0';

      /* Search the directory for the program.  */
      if (search_dir (dir, prog, MAX_PATH, absname) > 0)
	return strdup (absname);
      else
	return NULL;
    }

  if (GetCurrentDirectory (MAX_PATH, curdir) <= 0)
    return NULL;

  /* Relative path; search in current dir. */
  if (strpbrk (prog, "\\"))
    {
      if (search_dir (curdir, prog, MAX_PATH, absname) > 0)
	return strdup (absname);
      else
	return NULL;
    }

  /* Just filename; search current directory then PATH.  */
  path = alloca (strlen (getenv ("PATH")) + strlen (curdir) + 2);
  strcpy (path, curdir);
  strcat (path, ";");
  strcat (path, getenv ("PATH"));

  while (*path)
    {
      size_t len;

      /* Get next directory from path.  */
      p = path;
      while (*p && *p != ';') p++;
      /* A broken PATH could have too long directory names in it.  */
      len = min (p - path, sizeof (dir) - 1);
      strncpy (dir, path, len);
      dir[len] = '\0';

      /* Search the directory for the program.  */
      if (search_dir (dir, prog, MAX_PATH, absname) > 0)
	return strdup (absname);

      /* Move to the next directory.  */
      path = p + 1;
    }

  return NULL;
}

/* Try to decode the given command line the way cmd would do it.  On
   success, return 1 with cmdline dequoted.  Otherwise, when we've
   found constructs only cmd can properly interpret, return 0 and
   leave cmdline unchanged.  */
static int
try_dequote_cmdline (char* cmdline)
{
  /* Dequoting can only subtract characters, so the length of the
     original command line is a bound on the amount of scratch space
     we need.  This length, in turn, is bounded by the 32k
     CreateProcess limit.  */
  char * old_pos = cmdline;
  char * new_cmdline = alloca (strlen(cmdline));
  char * new_pos = new_cmdline;
  char c;

  enum {
    NORMAL,
    AFTER_CARET,
    INSIDE_QUOTE
  } state = NORMAL;

  while ((c = *old_pos++))
    {
      switch (state)
        {
        case NORMAL:
          switch(c)
            {
            case '"':
              *new_pos++ = c;
              state = INSIDE_QUOTE;
              break;
            case '^':
              state = AFTER_CARET;
              break;
            case '<': case '>':
            case '&': case '|':
            case '(': case ')':
            case '%': case '!':
              /* We saw an unquoted shell metacharacter and we don't
                 understand it. Bail out.  */
              return 0;
            default:
              *new_pos++ = c;
              break;
            }
          break;
        case AFTER_CARET:
          *new_pos++ = c;
          state = NORMAL;
          break;
        case INSIDE_QUOTE:
          switch (c)
            {
            case '"':
              *new_pos++ = c;
              state = NORMAL;
              break;
            case '%':
            case '!':
              /* Variable substitution inside quote.  Bail out.  */
              return 0;
            default:
              *new_pos++ = c;
              break;
            }
          break;
        }
    }

  /* We were able to dequote the entire string.  Copy our scratch
     buffer on top of the original buffer and return success.  */
  memcpy (cmdline, new_cmdline, new_pos - new_cmdline);
  cmdline[new_pos - new_cmdline] = '\0';
  return 1;
}

/*****************************************************************/

#if 0
char ** _argv;
int     _argc;

/* Parse commandline into argv array, allowing proper quoting of args.  */
void
setup_argv (void)
{
  char * cmdline = GetCommandLine ();
  int arg_bytes = 0;


}
#endif

/* Information about child proc is global, to allow for automatic
   termination when interrupted.  At the moment, only one child process
   can be running at any one time.  */

PROCESS_INFORMATION child;
int interactive = TRUE;

BOOL console_event_handler (DWORD);

BOOL
console_event_handler (DWORD event)
{
  switch (event)
    {
    case CTRL_C_EVENT:
    case CTRL_BREAK_EVENT:
      if (!interactive)
	{
	  /* Both command.com and cmd.exe have the annoying behavior of
	     prompting "Terminate batch job (y/n)?" when interrupted
	     while running a batch file, even if running in
	     non-interactive (-c) mode.  Try to make up for this
	     deficiency by forcibly terminating the subprocess if
	     running non-interactively.  */
	  if (child.hProcess &&
	      WaitForSingleObject (child.hProcess, 500) != WAIT_OBJECT_0)
	    TerminateProcess (child.hProcess, 0);
	  exit (STATUS_CONTROL_C_EXIT);
	}
      break;

#if 0
    default:
      /* CLOSE, LOGOFF and SHUTDOWN events - actually we don't get these
         under Windows 95.  */
      fail ("cmdproxy: received %d event\n", event);
      if (child.hProcess)
	TerminateProcess (child.hProcess, 0);
#endif
    }
  return TRUE;
}

/* Change from normal usage; return value indicates whether spawn
   succeeded or failed - program return code is returned separately.  */
static int
spawn (const char *progname, char *cmdline, const char *dir, int *retcode)
{
  BOOL success = FALSE;
  SECURITY_ATTRIBUTES sec_attrs;
  STARTUPINFO start;
  /* In theory, passing NULL for the environment block to CreateProcess
     is the same as passing the value of GetEnvironmentStrings, but
     doing this explicitly seems to cure problems running DOS programs
     in some cases.  */
  char * envblock = GetEnvironmentStrings ();

  sec_attrs.nLength = sizeof (sec_attrs);
  sec_attrs.lpSecurityDescriptor = NULL;
  sec_attrs.bInheritHandle = FALSE;

  memset (&start, 0, sizeof (start));
  start.cb = sizeof (start);

  /* CreateProcess handles batch files as progname specially. This
     special handling fails when both the batch file and arguments are
     quoted.  We pass NULL as progname to avoid the special
     handling. */
  if (progname != NULL && cmdline[0] == '"' && batch_file_p (progname))
      progname = NULL;

  if (CreateProcess (progname, cmdline, &sec_attrs, NULL, TRUE,
		     0, envblock, dir, &start, &child))
  {
    success = TRUE;
    /* wait for completion and pass on return code */
    WaitForSingleObject (child.hProcess, INFINITE);
    if (retcode)
      GetExitCodeProcess (child.hProcess, (DWORD *)retcode);
    CloseHandle (child.hThread);
    CloseHandle (child.hProcess);
    child.hProcess = NULL;
  }

  FreeEnvironmentStrings (envblock);

  return success;
}

/* Return size of current environment block.  */
static int
get_env_size (void)
{
  char * start = GetEnvironmentStrings ();
  char * tmp = start;

  while (tmp[0] || tmp[1])
    ++tmp;
  FreeEnvironmentStrings (start);
  return  tmp + 2 - start;
}

/*******  Main program  ********************************************/

int
main (int argc, char ** argv)
{
  int rc;
  int need_shell;
  char * cmdline;
  char * progname;
  int envsize;
  char **pass_through_args;
  int num_pass_through_args;
  char modname[MAX_PATH];
  char path[MAX_PATH];
  char dir[MAX_PATH];
  int status;

  interactive = TRUE;

  SetConsoleCtrlHandler ((PHANDLER_ROUTINE) console_event_handler, TRUE);

  if (!GetCurrentDirectory (sizeof (dir), dir))
    fail ("error: GetCurrentDirectory failed\n");

  /* We serve double duty: we can be called either as a proxy for the
     real shell (that is, because we are defined to be the user shell),
     or in our role as a helper application for running DOS programs.
     In the former case, we interpret the command line options as if we
     were a Unix shell, but in the latter case we simply pass our
     command line to CreateProcess.  We know which case we are dealing
     with by whether argv[0] refers to ourself or to some other program.
     (This relies on an arcane feature of CreateProcess, where we can
     specify cmdproxy as the module to run, but specify a different
     program in the command line - the MSVC startup code sets argv[0]
     from the command line.)  */

  if (!GetModuleFileName (NULL, modname, sizeof (modname)))
    fail ("error: GetModuleFileName failed\n");

  /* Change directory to location of .exe so startup directory can be
     deleted.  */
  progname = strrchr (modname, '\\');
  *progname = '\0';
  SetCurrentDirectory (modname);
  *progname = '\\';

  /* Due to problems with interaction between API functions that use "OEM"
     codepage vs API functions that use the "ANSI" codepage, we need to
     make things consistent by choosing one and sticking with it.  */
  SetConsoleCP (GetACP ());
  SetConsoleOutputCP (GetACP ());

  /* Although Emacs always sets argv[0] to an absolute pathname, we
     might get run in other ways as well, so convert argv[0] to an
     absolute name before comparing to the module name.  */
  path[0] = '\0';
  /* The call to SearchPath will find argv[0] in the current
     directory, append ".exe" to it if needed, and also canonicalize
     it, to resolve references to ".", "..", etc.  */
  status = SearchPath (NULL, argv[0], ".exe", sizeof (path), path,
				  &progname);
  if (!(status > 0 && stricmp (modname, path) == 0))
    {
      if (status <= 0)
	{
	  char *s;

	  /* Make sure we have argv[0] in path[], as the failed
	     SearchPath might not have copied it there.  */
	  strcpy (path, argv[0]);
	  /* argv[0] could include forward slashes; convert them all
	     to backslashes, for strrchr calls below to DTRT.  */
	  for (s = path; *s; s++)
	    if (*s == '/')
	      *s = '\\';
	}
      /* Perhaps MODNAME and PATH use mixed short and long file names.  */
      if (!(GetShortPathName (modname, modname, sizeof (modname))
	    && GetShortPathName (path, path, sizeof (path))
	    && stricmp (modname, path) == 0))
	{
	  /* Sometimes GetShortPathName fails because one or more
	     directories leading to argv[0] have issues with access
	     rights.  In that case, at least we can compare the
	     basenames.  Note: this disregards the improbable case of
	     invoking a program of the same name from another
	     directory, since the chances of that other executable to
	     be both our namesake and a 16-bit DOS application are nil.  */
	  char *p = strrchr (path, '\\');
	  char *q = strrchr (modname, '\\');
	  char *pdot, *qdot;

	  if (!p)
	    p = strchr (path, ':');
	  if (!p)
	    p = path;
	  else
	    p++;
	  if (!q)
	    q = strchr (modname, ':');
	  if (!q)
	    q = modname;
	  else
	    q++;

	  pdot = strrchr (p, '.');
	  if (!pdot || stricmp (pdot, ".exe") != 0)
	    pdot = p + strlen (p);
	  qdot = strrchr (q, '.');
	  if (!qdot || stricmp (qdot, ".exe") != 0)
	    qdot = q + strlen (q);
	  if (pdot - p != qdot - q || strnicmp (p, q, pdot - p) != 0)
	    {
	      /* We are being used as a helper to run a DOS app; just
		 pass command line to DOS app without change.  */
	      /* TODO: fill in progname.  */
	      if (spawn (NULL, GetCommandLine (), dir, &rc))
		return rc;
	      fail ("Could not run %s\n", GetCommandLine ());
	    }
	}
    }

  /* Process command line.  If running interactively (-c or /c not
     specified) then spawn a real command shell, passing it the command
     line arguments.

     If not running interactively, then attempt to execute the specified
     command directly.  If necessary, spawn a real shell to execute the
     command.

  */

  progname = NULL;
  cmdline = NULL;
  /* If no args, spawn real shell for interactive use.  */
  need_shell = TRUE;
  interactive = TRUE;
  /* Ask command.com to create an environment block with a reasonable
     amount of free space.  */
  envsize = get_env_size () + 300;
  pass_through_args = (char **) alloca (argc * sizeof (char *));
  num_pass_through_args = 0;

  while (--argc > 0)
    {
      ++argv;
      /* Act on switches we recognize (mostly single letter switches,
	 except for -e); all unrecognized switches and extra args are
	 passed on to real shell if used (only really of benefit for
	 interactive use, but allow for batch use as well).  Accept / as
	 switch char for compatibility with cmd.exe.  */
      if (((*argv)[0] == '-' || (*argv)[0] == '/') && (*argv)[1] != '\0')
	{
	  if (((*argv)[1] == 'c' || (*argv)[1] == 'C') && ((*argv)[2] == '\0'))
	    {
	      if (--argc == 0)
		fail ("error: expecting arg for %s\n", *argv);
	      cmdline = *(++argv);
	      interactive = FALSE;
	    }
	  else if (((*argv)[1] == 'i' || (*argv)[1] == 'I') && ((*argv)[2] == '\0'))
	    {
	      if (cmdline)
		warn ("warning: %s ignored because of -c\n", *argv);
	    }
	  else if (((*argv)[1] == 'e' || (*argv)[1] == 'E') && ((*argv)[2] == ':'))
	    {
	      int requested_envsize = atoi (*argv + 3);
	      /* Enforce a reasonable minimum size, as above.  */
	      if (requested_envsize > envsize)
		envsize = requested_envsize;
	      /* For sanity, enforce a reasonable maximum.  */
	      if (envsize > 32768)
		envsize = 32768;
	    }
	  else
	    {
	      /* warn ("warning: unknown option %s ignored", *argv); */
	      pass_through_args[num_pass_through_args++] = *argv;
	    }
	}
      else
	break;
    }

#if 0
  /* I think this is probably not useful - cmd.exe ignores extra
     (non-switch) args in interactive mode, and they cannot be passed on
     when -c was given.  */

  /* Collect any remaining args after (initial) switches.  */
  while (argc-- > 0)
    {
      pass_through_args[num_pass_through_args++] = *argv++;
    }
#else
  /* Probably a mistake for there to be extra args; not fatal.  */
  if (argc > 0)
    warn ("warning: extra args ignored after '%s'\n", argv[-1]);
#endif

  pass_through_args[num_pass_through_args] = NULL;

  /* If -c option, determine if we must spawn a real shell, or if we can
     execute the command directly ourself.  */
  if (cmdline)
    {
      const char *args;

      /* The program name is the first token of cmdline.  Since
         filenames cannot legally contain embedded quotes, the value
         of escape_char doesn't matter.  */
      args = cmdline;
      if (!get_next_token (path, &args))
        fail ("error: no program name specified.\n");

      canon_filename (path);
      progname = make_absolute (path);

      /* If we found the program and the rest of the command line does
         not contain unquoted shell metacharacters, run the program
         directly (if not found it might be an internal shell command,
         so don't fail).  */
      if (progname != NULL && try_dequote_cmdline (cmdline))
        need_shell = FALSE;
      else
        progname = NULL;
    }

 pass_to_shell:
  if (need_shell)
    {
      char * p;
      int    extra_arg_space = 0;
      int    maxlen, remlen;
      int    run_command_dot_com;

      progname = getenv ("COMSPEC");
      if (!progname)
	fail ("error: COMSPEC is not set\n");

      canon_filename (progname);
      progname = make_absolute (progname);

      if (progname == NULL || strchr (progname, '\\') == NULL)
	fail ("error: the program %s could not be found.\n", getenv ("COMSPEC"));

      /* Need to set environment size when running command.com.  */
      run_command_dot_com =
	(stricmp (strrchr (progname, '\\'), "command.com") == 0);

      /* Work out how much extra space is required for
         pass_through_args.  */
      for (argv = pass_through_args; *argv != NULL; ++argv)
	/* We don't expect to have to quote switches.  */
	extra_arg_space += strlen (*argv) + 2;

      if (cmdline)
	{
	  char * buf;

	  /* Convert to syntax expected by cmd.exe/command.com for
	     running non-interactively.  Always quote program name in
	     case path contains spaces (fortunately it can't contain
	     quotes, since they are illegal in path names).  */

	  remlen = maxlen =
	    strlen (progname) + extra_arg_space + strlen (cmdline) + 16 + 2;
	  buf = p = alloca (maxlen + 1);

	  /* Quote progname in case it contains spaces.  */
	  p += _snprintf (p, remlen, "\"%s\"", progname);
	  remlen = maxlen - (p - buf);

	  /* Include pass_through_args verbatim; these are just switches
             so should not need quoting.  */
	  for (argv = pass_through_args; *argv != NULL; ++argv)
	    {
	      p += _snprintf (p, remlen, " %s", *argv);
	      remlen = maxlen - (p - buf);
	    }

	  /* Now that we know we will be invoking the shell, quote the
	     command line after the "/c" switch as the shell expects:
	     a single pair of quotes enclosing the entire command
	     tail, no matter whether quotes are used in the command
	     line, and how many of them are there.  See the output of
	     "cmd /?" for how cmd.exe treats quotes.  */
	  if (run_command_dot_com)
	    _snprintf (p, remlen, " /e:%d /c \"%s\"", envsize, cmdline);
	  else
	    _snprintf (p, remlen, " /c \"%s\"", cmdline);
	  cmdline = buf;
	}
      else
	{
	  if (run_command_dot_com)
	    {
	      /* Provide dir arg expected by command.com when first
		 started interactively (the "command search path").  To
		 avoid potential problems with spaces in command dir
		 (which cannot be quoted - command.com doesn't like it),
		 we always use the 8.3 form.  */
	      GetShortPathName (progname, path, sizeof (path));
	      p = strrchr (path, '\\');
	      /* Trailing slash is acceptable, so always leave it.  */
	      *(++p) = '\0';
	    }
	  else
	    path[0] = '\0';

	  remlen = maxlen =
	    strlen (progname) + extra_arg_space + strlen (path) + 13;
	  cmdline = p = alloca (maxlen + 1);

	  /* Quote progname in case it contains spaces.  */
	  p += _snprintf (p, remlen, "\"%s\" %s", progname, path);
	  remlen = maxlen - (p - cmdline);

	  /* Include pass_through_args verbatim; these are just switches
             so should not need quoting.  */
	  for (argv = pass_through_args; *argv != NULL; ++argv)
	    {
	      p += _snprintf (p, remlen, " %s", *argv);
	      remlen = maxlen - (p - cmdline);
	    }

	  if (run_command_dot_com)
	    _snprintf (p, remlen, " /e:%d", envsize);
	}
    }

  if (!progname)
    fail ("Internal error: program name not defined\n");

  if (!cmdline)
    cmdline = progname;

  if (spawn (progname, cmdline, dir, &rc))
    return rc;

  if (!need_shell)
    {
      need_shell = TRUE;
      goto pass_to_shell;
    }

  fail ("Could not run %s\n", progname);

  return 0;
}