Re: [PATCH] remove unnecessary loop

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According to Alex Riesen on 5/8/2007 3:08 AM:

It is a limitation of cygwin, and the cygwin developers will admit it; but they will also stand behind calling it a feature rather than a bug due to the attempts to make cygwin behave more like Linux in spite of Window's insistence on file suffixes. The cygwin port of coreutils has to do similar stat() tricks to reverse engineer some of the .exe magic present in cygwin. However, it is possible to override the magic without resorting to a full-blown open(), via careful use of additional stat()s or readlink()s (trailing . is not legal in Windows, and on cygwin is only legal on managed mounts, so stat("foo.") will fail when stat("foo") succeeds if the reason stat("foo") succeeded was due only to the existence of foo.exe):

/* Return -1 if PATH not found, 0 if PATH spelled correctly, and 1 if PATH
   had ".exe" automatically appended by cygwin.  Don't change errno.  */
int
cygwin_spelling (char const *path)
{
  char path_exact[PATH_MAX + 9];
  int saved_errno = errno;
  int result = 0; /* Start with assumption that PATH is okay.  */
  int len = strlen (path);

  if (! path || ! *path || len > PATH_MAX)
    /* PATH will cause EINVAL or ENAMETOOLONG, treat it as non-existing.  */
    return -1;
  if (path[len - 1] == '.' || path[len-1] == '/')
    /* Don't change spelling if there is a trailing `.' or `/'.  */
    return 0;
  if (readlink (path, NULL, 0) < 0)
    { /* PATH is not a symlink.  */
      if (errno == EINVAL)
	{ /* PATH exists.  Appending trailing `.' exposes whether it is
	     PATH or PATH.exe for normal disk files, but also check appending
	     trailing `.exe' to be sure on virtual/managed directories.  */
	  strcat (strcpy (path_exact, path), ".");
	  if (access (path_exact, F_OK) < 0)
	    { /* PATH. does not exist.  */
	      strcat (path_exact, "exe");
	      if (access (path_exact, F_OK) == 0)
		/* But PATH.exe does, so append .exe.  */
		result = 1;
	    }
	}
      else
	/* PATH does not exist.  */
	result = -1;
    }
  else
    { /* PATH is a symlink.  Appending trailing `.lnk' exposes whether
	 it is PATH.lnk or PATH.exe.lnk; but does not help with
	 old-style symlinks where it was just PATH and the system
	 attribute set.  */
      strcat (strcpy (path_exact, path), ".lnk");
      if (readlink (path_exact, NULL, 0) < 0)
	{
	  strcat (strcpy (path_exact, path), ".exe.lnk");
	  if (readlink (path_exact, NULL, 0) == 0)
	    result = 1;
	}
    }

  errno = saved_errno;
  return result;
}

In the upcoming cygwin 1.7.0, you can set CYGWIN=transparent_exe which will cause ENOENT when dealing with any explicit .exe. When enabled, that will make it impossible to have both foo and foo.exe in the current directory, and make it so that stat can never lie - stat("foo.exe") will fail, and if stat("foo") succeeds, you no longer care if it succeeded because of the Windows file foo or because of foo.exe, because the .exe is transparent to cygwin.

- --
Don't work too hard, make some time for fun as well!

Eric Blake             ebb9@byu.net
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