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/* Call execve (), handling interpreting shell scripts, and handling
   exec failures. */
int
shell_execve (char *command, char **args, char **env)
{
  int i, fd, sample_len;
  char sample[HASH_BANG_BUFSIZ];
  size_t larray;

  SETOSTYPE (0);		/* Some systems use for USG/POSIX semantics */
  execve (command, args, env);
  i = errno;			/* error from execve() */
  CHECK_TERMSIG;
  SETOSTYPE (1);

  /* If we get to this point, then start checking out the file.
     Maybe it is something we can hack ourselves. */
  if (i != ENOEXEC)
    {
      /* make sure this is set correctly for file_error/report_error */
      last_command_exit_value = (i == ENOENT) ?  EX_NOTFOUND : EX_NOEXEC; /* XXX Posix.2 says that exit status is 126 */
      if (file_isdir (command))
#if defined (EISDIR)
	internal_error ("%s: %s", command, strerror (EISDIR));
#else
	internal_error (_("%s: is a directory"), command);
#endif
      else if (executable_file (command) == 0)
	{
	  errno = i;
	  file_error (command);
	}
      /* errors not involving the path argument to execve. */
      else if (i == E2BIG || i == ENOMEM)
	{
	  errno = i;
	  file_error (command);
	}
      else
	{
	  /* The file has the execute bits set, but the kernel refuses to
	     run it for some reason.  See why. */
#if defined (HAVE_HASH_BANG_EXEC)
	  READ_SAMPLE_BUF (command, sample, sample_len);
	  if (sample_len > 0)
	    sample[sample_len - 1] = '\0';
	  if (sample_len > 2 && sample[0] == '#' && sample[1] == '!')
	    {
	      char *interp;
	      size_t ilen;

	      interp = getinterp (sample, sample_len, (int *)NULL);
	      ilen = strlen (interp);
	      errno = i;
	      if (ilen > 0 && interp[ilen - 1] == '\r')
		{
		  interp = xrealloc (interp, ilen + 2);
		  interp[ilen - 1] = '^';
		  interp[ilen] = 'M';
		  interp[ilen + 1] = '\0';
		}
	      sys_error ("%s: %s: %s", command, interp, _("bad interpreter"));
	      FREE (interp);
	      return (EX_NOEXEC);
	    }
	  else
#endif
	  if (i == ENOENT)
	    {
	      errno = i;
	      internal_error (_("%s: cannot execute: required file not found"), command);
	    }
	  else
	    {
	      errno = i;
	      file_error (command);
	    }
	}
      return (last_command_exit_value);
    }

  /* This file is executable.
     If it begins with #!, then help out people with losing operating
     systems.  Otherwise, check to see if it is a binary file by seeing
     if the contents of the first line (or up to 80 characters) are in the
     ASCII set.  If it's a text file, execute the contents as shell commands,
     otherwise return 126 (EX_BINARY_FILE). */
  READ_SAMPLE_BUF (command, sample, sample_len);

  if (sample_len == 0)
    return (EXECUTION_SUCCESS);

  /* Is this supposed to be an executable script?
     If so, the format of the line is "#! interpreter [argument]".
     A single argument is allowed.  The BSD kernel restricts
     the length of the entire line to 32 characters (32 bytes
     being the size of the BSD exec header), but we allow up to 128
     characters. */
  if (sample_len > 0)
    {
#if !defined (HAVE_HASH_BANG_EXEC)
      if (sample_len > 2 && sample[0] == '#' && sample[1] == '!')
	return (execute_shell_script (sample, sample_len, command, args, env));
      else
#endif
      if (check_binary_file (sample, sample_len))
	{
	  internal_error ("%s: %s: %s", command, _("cannot execute binary file"), strerror (i));
	  errno = i;
	  return (EX_BINARY_FILE);
	}
    }

  /* We have committed to attempting to execute the contents of this file
     as shell commands. */

  reset_parser ();
  initialize_subshell ();

  set_sigint_handler ();

  /* Insert the name of this shell into the argument list. */
  larray = strvec_len (args) + 1;
  args = strvec_resize (args, larray + 1);

  for (i = larray - 1; i; i--)
    args[i] = args[i - 1];

  args[0] = shell_name;
  args[1] = command;
  args[larray] = (char *)NULL;

  if (args[0][0] == '-')
    args[0]++;

#if defined (RESTRICTED_SHELL)
  if (restricted)
    change_flag ('r', FLAG_OFF);
#endif

  if (subshell_argv)
    {
      /* Can't free subshell_argv[0]; that is shell_name. */
      for (i = 1; i < subshell_argc; i++)
	free (subshell_argv[i]);
      free (subshell_argv);
    }

  dispose_command (currently_executing_command);	/* XXX */
  currently_executing_command = (COMMAND *)NULL;

  subshell_argc = larray;
  subshell_argv = args;
  subshell_envp = env;

  unbind_args ();	/* remove the positional parameters */

#if defined (PROCESS_SUBSTITUTION) && defined (HAVE_DEV_FD)
  clear_fifo_list ();	/* pipe fds are what they are now */
#endif

  sh_longjmp (subshell_top_level, 1);
  /*NOTREACHED*/
}

static int
zexecve(char *pth, char **argv, char **newenvp)
{
    int eno;
    static char buf[PATH_MAX * 2+1];
    char **eep;

    unmetafy(pth, NULL);
    for (eep = argv; *eep; eep++)
	if (*eep != pth)
	    unmetafy(*eep, NULL);
    buf[0] = '_';
    buf[1] = '=';
    if (*pth == '/')
	strcpy(buf + 2, pth);
    else
	sprintf(buf + 2, "%s/%s", unmeta(pwd), pth);
    zputenv(buf);
#ifndef FD_CLOEXEC
    closedumps();
#endif

    if (newenvp == NULL)
	    newenvp = environ;
    winch_unblock();
    execve(pth, argv, newenvp);

    /* If the execve returns (which in general shouldn't happen),   *
     * then check for an errno equal to ENOEXEC.  This errno is set *
     * if the process file has the appropriate access permission,   *
     * but has an invalid magic number in its header.               */
    if ((eno = errno) == ENOEXEC || eno == ENOENT) {
	char execvebuf[POUNDBANGLIMIT + 1], *ptr, *ptr2, *argv0;
	int fd, ct, t0;

	if ((fd = open(pth, O_RDONLY|O_NOCTTY)) >= 0) {
	    argv0 = *argv;
	    *argv = pth;
	    memset(execvebuf, '\0', POUNDBANGLIMIT + 1);
	    ct = read(fd, execvebuf, POUNDBANGLIMIT);
	    close(fd);
	    if (ct >= 0) {
		if (ct >= 2 && execvebuf[0] == '#' && execvebuf[1] == '!') {
		    for (t0 = 0; t0 != ct; t0++)
			if (execvebuf[t0] == '\n')
			    break;
		    if (t0 == ct)
			zerr("%s: bad interpreter: %s: %e", pth,
			     metafy(execvebuf + 2, -1, META_STATIC), eno);
		    else {
			while (inblank(execvebuf[t0]))
			    execvebuf[t0--] = '\0';
			for (ptr = execvebuf + 2; *ptr && *ptr == ' '; ptr++);
			for (ptr2 = ptr; *ptr && *ptr != ' '; ptr++);
			if (eno == ENOENT) {
			    char *pprog;
			    if (*ptr)
				*ptr = '\0';
			    if (*ptr2 != '/' &&
				(pprog = pathprog(ptr2, NULL))) {
				if (ptr == execvebuf + t0 + 1) {
				    argv[-1] = ptr2;
				    winch_unblock();
				    execve(pprog, argv - 1, newenvp);
				} else {
				    argv[-2] = ptr2;
				    argv[-1] = ptr + 1;
				    winch_unblock();
				    execve(pprog, argv - 2, newenvp);
				}
			    }
			    zerr("%s: bad interpreter: %s: %e", pth,
				 metafy(ptr2, -1, META_STATIC), eno);
			} else if (*ptr) {
			    *ptr = '\0';
			    argv[-2] = ptr2;
			    argv[-1] = ptr + 1;
			    winch_unblock();
			    execve(ptr2, argv - 2, newenvp);
			} else {
			    argv[-1] = ptr2;
			    winch_unblock();
			    execve(ptr2, argv - 1, newenvp);
			}
		    }
		} else if (eno == ENOEXEC) {
                    /* Perform binary safety check on classic shell    *
                     * scripts (shebang wasn't introduced until UNIX   *
                     * Seventh Edition). POSIX says we shall allow     *
                     * execution of scripts with concatenated binary   *
                     * and suggests checking a line exists before the  *
                     * first NUL character with a lowercase letter or  *
                     * expansion. This is consistent with FreeBSD sh.  */
                    int isbinary, hasletter;
                    if (!(ptr2 = memchr(execvebuf, '\0', ct))) {
                        isbinary = 0;
                    } else {
                        isbinary = 1;
                        hasletter = 0;
                        for (ptr = execvebuf; ptr < ptr2; ptr++) {
			    if (islower((unsigned char) *ptr) || *ptr == '$' || *ptr == '`')
                                hasletter = 1;
                            if (hasletter && *ptr == '\n') {
                                isbinary = 0;
                                break;
                            }
                        }
                    }
		    if (!isbinary) {
		        char** args = argv;
			if (argv[0][0] == '-' || argv[0][0] == '+') {
			    /*
			     * guard against +foo or -bar script paths being
			     * taken as options. POSIX says the script path
			     * must be passed as an *operand*. "--" would also
			     * make sure the next argument is treated as an
			     * operand with POSIX compliant sh implementations
			     * but "-" is more portable (to the Bourne shell in
			     * particular) and shorter.
			     */
			    *--args = "-";
			}
			*--args = "sh";
			winch_unblock();
			execve("/bin/sh", args, newenvp);
		    }
		}
	    } else
		eno = errno;
	    *argv = argv0;
	} else
	    eno = errno;
    }
    /* restore the original arguments and path but do not bother with *
     * null characters as these cannot be passed to external commands *
     * anyway.  So the result is truncated at the first null char.    */
    pth = metafy(pth, -1, META_NOALLOC);
    for (eep = argv; *eep; eep++)
	if (*eep != pth)
	    (void) metafy(*eep, -1, META_NOALLOC);
    return eno;
}