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Filesystem(3)		    Tcl Library Procedures		 Filesystem(3)

______________________________________________________________________________

NAME
       Tcl_FSRegister,	 Tcl_FSUnregister,   Tcl_FSData,  Tcl_FSMountsChanged,
       Tcl_FSGetFileSystemForPath,     Tcl_FSGetPathType,      Tcl_FSCopyFile,
       Tcl_FSCopyDirectory, Tcl_FSCreateDirectory, Tcl_FSDeleteFile, Tcl_FSRe‐
       moveDirectory,  Tcl_FSRenameFile,  Tcl_FSListVolumes,   Tcl_FSEvalFile,
       Tcl_FSEvalFileEx, Tcl_FSLoadFile, Tcl_FSUnloadFile, Tcl_FSMatchInDirec‐
       tory,   Tcl_FSLink,   Tcl_FSLstat,   Tcl_FSUtime,   Tcl_FSFileAttrsGet,
       Tcl_FSFileAttrsSet,  Tcl_FSFileAttrStrings,  Tcl_FSStat,	 Tcl_FSAccess,
       Tcl_FSOpenFileChannel, Tcl_FSGetCwd, Tcl_FSChdir,  Tcl_FSPathSeparator,
       Tcl_FSJoinPath, Tcl_FSSplitPath, Tcl_FSEqualPaths, Tcl_FSGetNormalized‐
       Path, Tcl_FSJoinToPath, Tcl_FSConvertToPathType,	 Tcl_FSGetInternalRep,
       Tcl_FSGetTranslatedPath,	  Tcl_FSGetTranslatedStringPath,  Tcl_FSNewNa‐
       tivePath, Tcl_FSGetNativePath, Tcl_FSFileSystemInfo, Tcl_GetAccessTime‐
       FromStat,	Tcl_GetBlockSizeFromStat,	Tcl_GetBlocksFromStat,
       Tcl_GetChangeTimeFromStat, Tcl_GetDeviceTypeFromStat,  Tcl_GetFSDevice‐
       FromStat,	Tcl_GetFSInodeFromStat,	       Tcl_GetGroupIdFromStat,
       Tcl_GetLinkCountFromStat, Tcl_GetModeFromStat, Tcl_GetModificationTime‐
       FromStat,  Tcl_GetSizeFromStat, Tcl_GetUserIdFromStat, Tcl_AllocStatBuf
       - procedures to interact with any filesystem

SYNOPSIS
       #include <tcl.h>

       int
       Tcl_FSRegister(clientData, fsPtr)

       int
       Tcl_FSUnregister(fsPtr)

       ClientData
       Tcl_FSData(fsPtr)

       void
       Tcl_FSMountsChanged(fsPtr)

       const Tcl_Filesystem *
       Tcl_FSGetFileSystemForPath(pathPtr)

       Tcl_PathType
       Tcl_FSGetPathType(pathPtr)

       int
       Tcl_FSCopyFile(srcPathPtr, destPathPtr)

       int
       Tcl_FSCopyDirectory(srcPathPtr, destPathPtr, errorPtr)

       int
       Tcl_FSCreateDirectory(pathPtr)

       int
       Tcl_FSDeleteFile(pathPtr)

       int
       Tcl_FSRemoveDirectory(pathPtr, int recursive, errorPtr)

       int
       Tcl_FSRenameFile(srcPathPtr, destPathPtr)

       Tcl_Obj *
       Tcl_FSListVolumes(void)

       int
       Tcl_FSEvalFileEx(interp, pathPtr, encodingName)

       int
       Tcl_FSEvalFile(interp, pathPtr)

       int
       Tcl_FSLoadFile(interp, pathPtr, sym1, sym2, proc1Ptr, proc2Ptr,
		      loadHandlePtr, unloadProcPtr)

       int								       │
       Tcl_FSUnloadFile(interp, loadHandle)				       │

       int
       Tcl_FSMatchInDirectory(interp, resultPtr, pathPtr, pattern, types)

       Tcl_Obj *
       Tcl_FSLink(linkNamePtr, toPtr, linkAction)

       int
       Tcl_FSLstat(pathPtr, statPtr)

       int
       Tcl_FSUtime(pathPtr, tval)

       int
       Tcl_FSFileAttrsGet(interp, int index, pathPtr, objPtrRef)

       int
       Tcl_FSFileAttrsSet(interp, int index, pathPtr, Tcl_Obj *objPtr)

       const char *const *
       Tcl_FSFileAttrStrings(pathPtr, objPtrRef)

       int
       Tcl_FSStat(pathPtr, statPtr)

       int
       Tcl_FSAccess(pathPtr, mode)

       Tcl_Channel
       Tcl_FSOpenFileChannel(interp, pathPtr, modeString, permissions)

       Tcl_Obj *
       Tcl_FSGetCwd(interp)

       int
       Tcl_FSChdir(pathPtr)

       Tcl_Obj *
       Tcl_FSPathSeparator(pathPtr)

       Tcl_Obj *
       Tcl_FSJoinPath(listObj, elements)

       Tcl_Obj *
       Tcl_FSSplitPath(pathPtr, lenPtr)

       int
       Tcl_FSEqualPaths(firstPtr, secondPtr)

       Tcl_Obj *
       Tcl_FSGetNormalizedPath(interp, pathPtr)

       Tcl_Obj *
       Tcl_FSJoinToPath(basePtr, objc, objv)

       int
       Tcl_FSConvertToPathType(interp, pathPtr)

       ClientData
       Tcl_FSGetInternalRep(pathPtr, fsPtr)

       Tcl_Obj *
       Tcl_FSGetTranslatedPath(interp, pathPtr)

       const char *
       Tcl_FSGetTranslatedStringPath(interp, pathPtr)

       Tcl_Obj *
       Tcl_FSNewNativePath(fsPtr, clientData)

       const void *
       Tcl_FSGetNativePath(pathPtr)

       Tcl_Obj *
       Tcl_FSFileSystemInfo(pathPtr)

       Tcl_StatBuf *
       Tcl_AllocStatBuf()

       Tcl_WideInt							       │
       Tcl_GetAccessTimeFromStat(statPtr)				       │

       unsigned								       │
       Tcl_GetBlockSizeFromStat(statPtr)				       │

       Tcl_WideUInt							       │
       Tcl_GetBlocksFromStat(statPtr)					       │

       Tcl_WideInt							       │
       Tcl_GetChangeTimeFromStat(statPtr)				       │

       int								       │
       Tcl_GetDeviceTypeFromStat(statPtr)				       │

       unsigned								       │
       Tcl_GetFSDeviceFromStat(statPtr)					       │

       unsigned								       │
       Tcl_GetFSInodeFromStat(statPtr)					       │

       int								       │
       Tcl_GetGroupIdFromStat(statPtr)					       │

       int								       │
       Tcl_GetLinkCountFromStat(statPtr)				       │

       unsigned								       │
       Tcl_GetModeFromStat(statPtr)					       │

       Tcl_WideInt							       │
       Tcl_GetModificationTimeFromStat(statPtr)				       │

       Tcl_WideUInt							       │
       Tcl_GetSizeFromStat(statPtr)					       │

       int								       │
       Tcl_GetUserIdFromStat(statPtr)ARGUMENTS
       const Tcl_Filesystem *fsPtr (in)		   Points to a structure  con‐
						   taining  the	 addresses  of
						   procedures  that   can   be
						   called to perform the vari‐
						   ous filesystem operations.

       Tcl_Obj *pathPtr (in)			   The	path  represented   by
						   this	 value is used for the
						   operation in	 question.  If
						   the	value does not already
						   have an internal path  rep‐
						   resentation,	  it  will  be
						   converted to have one.

       Tcl_Obj *srcPathPtr (in)			   As for  pathPtr,  but  used
						   for	the  source file for a
						   copy or rename operation.

       Tcl_Obj *destPathPtr (in)		   As for  pathPtr,  but  used
						   for	the  destination file‐
						   name for a copy  or	rename
						   operation.

       const char *encodingName (in)		   The	encoding  of  the data
						   stored in the file  identi‐
						   fied	 by  pathPtr and to be
						   evaluated.

       const char *pattern (in)			   Only files  or  directories
						   matching  this pattern will
						   be returned.

       Tcl_GlobTypeData *types (in)		   Only files  or  directories
						   matching  the type descrip‐
						   tions  contained  in	  this
						   structure will be returned.
						   This parameter may be NULL.

       Tcl_Interp *interp (in)			   Interpreter to  use	either
						   for results, evaluation, or
						   reporting error messages.

       ClientData clientData (in)		   The native  description  of
						   the path value to create.

       Tcl_Obj *firstPtr (in)			   The	first of two path val‐
						   ues to compare.  The	 value
						   may	be  converted  to path
						   type.

       Tcl_Obj *secondPtr (in)			   The second of two path val‐
						   ues	to  compare. The value
						   may be  converted  to  path
						   type.

       Tcl_Obj *listObj (in)			   The	list  of path elements
						   to operate on with  a  join
						   operation.

       int elements (in)			   If non-negative, the number
						   of elements in the  listObj
						   which   should   be	joined
						   together. If negative, then
						   all elements are joined.

       Tcl_Obj **errorPtr (out)			   In  the  case  of an error,
						   filled with	a  value  con‐
						   taining  the	 name  of  the
						   file which caused an	 error
						   in  the various copy/rename
						   operations.

       Tcl_Obj **objPtrRef (out)		   Filled with	a  value  con‐
						   taining  the	 result of the
						   operation.

       Tcl_Obj *resultPtr (out)			   Pre-allocated   value    in
						   which   to	store	(using
						   Tcl_ListObjAppendElement)
						   the list of files or direc‐
						   tories which	 are  success‐
						   fully matched.

       int mode (in)				   Mask	 consisting  of one or
						   more of  R_OK,  W_OK,  X_OK
						   and	F_OK.  R_OK,  W_OK and
						   X_OK	   request    checking
						   whether the file exists and
						   has	read, write and	  exe‐
						   cute	  permissions, respec‐
						   tively. F_OK just  requests
						   checking  for the existence
						   of the file.

       Tcl_StatBuf *statPtr (out)		   The structure that contains
						   the	result	of  a  stat or
						   lstat operation.

       const char *sym1 (in)			   Name of a procedure to look
						   up in the file's symbol ta‐
						   ble

       const char *sym2 (in)			   Name of a procedure to look
						   up in the file's symbol ta‐
						   ble

       Tcl_PackageInitProc **proc1Ptr (out)	   Filled with the init	 func‐
						   tion for this code.

       Tcl_PackageInitProc **proc2Ptr (out)	   Filled  with	 the safe-init
						   function for this code.

       ClientData *clientDataPtr (out)		   Filled with the  clientData
						   value   to	pass  to  this
						   code's unload function when
						   it is called.

       Tcl_LoadHandle *loadHandlePtr (out)	   Filled   with  an  abstract
						   token   representing	   the
						   loaded file.

       Tcl_FSUnloadFileProc **unloadProcPtr (out)  Filled with the function to
						   use to unload this piece of
						   code.

       Tcl_LoadHandle loadHandle (in)		   Handle    to	  the	loaded
						   library to be unloaded.

       utimbuf *tval (in)			   The access and modification
						   times in this structure are
						   read and used to set	 those
						   values for a given file.

       const char *modeString (in)		   Specifies  how  the file is
						   to be  accessed.  May  have
						   any	of  the values allowed
						   for the  mode  argument  to
						   the Tcl open command.

       int permissions (in)			   POSIX-style	    permission
						   flags such as  0644.	 If  a
						   new	file is created, these
						   permissions will be set  on
						   the created file.

       int *lenPtr (out)			   If  non-NULL,  filled  with
						   the number of  elements  in
						   the split path.

       Tcl_Obj *basePtr (in)			   The	base  path on to which
						   to join the given elements.
						   May be NULL.

       int objc (in)				   The	number	of elements in
						   objv.

       Tcl_Obj *const objv[] (in)		   The elements to join to the
						   given base path.

       Tcl_Obj *linkNamePtr (in)		   The	name of the link to be
						   created or read.

       Tcl_Obj *toPtr (in)			   What	  the	link	called
						   linkNamePtr	  should    be
						   linked to, or NULL  if  the
						   symbolic  link specified by
						   linkNamePtr is to be read.

       int linkAction (in)			   OR-ed combination of	 flags
						   indicating	what  kind  of
						   link	 should	  be   created
						   (will  be  ignored if toPtr
						   is NULL). Valid bits to set
						   are	       TCL_CREATE_SYM‐
						   BOLIC_LINK	and   TCL_CRE‐
						   ATE_HARD_LINK.   When  both
						   flags  are  set   and   the
						   underlying  filesystem  can
						   do either,  symbolic	 links
						   are preferred.
_________________________________________________________________

DESCRIPTION
       There  are  several  reasons  for  calling  the	Tcl_FS	API  functions
       (e.g. Tcl_FSAccess and Tcl_FSStat) rather  than	calling	 system	 level
       functions  like	access and stat directly. First, they will work cross-
       platform, so an extension which calls them should  work	unmodified  on
       Unix  and  Windows. Second, the Windows implementation of some of these
       functions fixes some bugs in the system level calls. Third, these func‐
       tion  calls  deal  with	any  “Utf to platform-native” path conversions
       which may be required (and may cache the results	 of  such  conversions
       for  greater  efficiency on subsequent calls). Fourth, and perhaps most
       importantly, all of these functions  are	 “virtual  filesystem  aware”.
       Any  virtual  filesystem	 (VFS  for  short)  which  has been registered
       (through Tcl_FSRegister) may reroute file access to  alternative	 media
       or  access  methods. This means that all of these functions (and there‐
       fore the corresponding file, glob, pwd, cd,  open,  etc. Tcl  commands)
       may  be	operate	 on  “files”  which are not native files in the native
       filesystem. This also means that any Tcl extension which	 accesses  the
       filesystem  (FS	for  short) through this API is automatically “virtual
       filesystem aware”.  Of course, if  an  extension	 accesses  the	native
       filesystem directly (through platform-specific APIs, for example), then
       Tcl cannot intercept such calls.

       If appropriate VFSes have been registered, the “files” may, to give two
       examples,  be remote (e.g. situated on a remote ftp server) or archived
       (e.g. lying inside a .zip archive). Such registered filesystems provide
       a lookup table of functions to implement all or some of the functional‐
       ity listed here. Finally, the Tcl_FSStat and Tcl_FSLstat calls abstract
       away  from  what	 the  “struct stat” buffer is actually declared to be,
       allowing the same code to be used both  on  systems  with  and  systems
       without support for files larger than 2GB in size.

       The  Tcl_FS API is Tcl_Obj-ified and may cache internal representations
       and other path-related strings (e.g. the	 current  working  directory).
       One side-effect of this is that one must not pass in values with a ref‐
       erence count of zero to any of these functions. If such calls were han‐
       dled,  they might result in memory leaks (under some circumstances, the
       filesystem code may wish to retain a reference to the passed in	value,
       and  so	one  must not assume that after any of these calls return, the
       value still has a reference count of zero - it  may  have  been	incre‐
       mented)	or  in	a  direct  segmentation	 fault (or other memory access
       error) due to the value being freed part way through the complex	 value
       manipulation  required  to ensure that the path is fully normalized and
       absolute for filesystem determination. The practical  lesson  to	 learn
       from this is that

	      Tcl_Obj *path = Tcl_NewStringObj(...);
	      Tcl_FSWhatever(path);
	      Tcl_DecrRefCount(path);

       is wrong, and may cause memory errors. The path must have its reference
       count incremented before passing it in, or decrementing	it.  For  this
       reason,	values with a reference count of zero are considered not to be
       valid filesystem paths and calling any Tcl_FS API function with such  a
       value will result in no action being taken.

   FS API FUNCTIONS
       Tcl_FSCopyFile  attempts	 to  copy  the file given by srcPathPtr to the
       path name given by destPathPtr. If the two paths given lie in the  same
       filesystem (according to Tcl_FSGetFileSystemForPath) then that filesys‐
       tem's “copy file” function is called (if it  is	non-NULL).   Otherwise
       the  function  returns  -1  and sets the errno global C variable to the
       “EXDEV” POSIX error code (which signifies a “cross-domain link”).

       Tcl_FSCopyDirectory attempts to copy the directory given by  srcPathPtr
       to  the	path  name given by destPathPtr. If the two paths given lie in
       the same filesystem (according to Tcl_FSGetFileSystemForPath) then that
       filesystem's  “copy file” function is called (if it is non-NULL).  Oth‐
       erwise the function returns -1 and sets the errno global C variable  to
       the “EXDEV” POSIX error code (which signifies a “cross-domain link”).

       Tcl_FSCreateDirectory attempts to create the directory given by pathPtr
       by calling the owning filesystem's “create directory” function.

       Tcl_FSDeleteFile attempts to delete the file given by pathPtr by	 call‐
       ing the owning filesystem's “delete file” function.

       Tcl_FSRemoveDirectory attempts to remove the directory given by pathPtr
       by calling the owning filesystem's “remove directory” function.

       Tcl_FSRenameFile attempts to rename the file or directory given by src‐
       PathPtr	to  the path name given by destPathPtr. If the two paths given
       lie in the same filesystem  (according  to  Tcl_FSGetFileSystemForPath)
       then  that filesystem's “rename file” function is called (if it is non-
       NULL). Otherwise the function returns -1 and sets the  errno  global  C
       variable	 to  the  “EXDEV”  POSIX error code (which signifies a “cross-
       domain link”).

       Tcl_FSListVolumes calls each filesystem which has a non-NULL “list vol‐
       umes”  function	and asks them to return their list of root volumes. It
       accumulates the return values in a list which is returned to the caller
       (with a reference count of 0).

       Tcl_FSEvalFileEx	 reads	the  file  given by pathPtr using the encoding
       identified by encodingName and evaluates its contents as a Tcl  script.
       It  returns  the same information as Tcl_EvalObjEx.  If encodingName is
       NULL, the system encoding is used for reading the  file	contents.   If
       the file could not be read then a Tcl error is returned to describe why
       the file could not be read.  The eofchar for files is  “\32”  (^Z)  for
       all  platforms.	 If  you require a “^Z” in code for string comparison,
       you can use “\032” or “\u001a”, which will be safely substituted by the
       Tcl  interpreter	 into  “^Z”.   Tcl_FSEvalFile  is a simpler version of
       Tcl_FSEvalFileEx that always uses the system encoding when reading  the
       file.

       Tcl_FSLoadFile  dynamically  loads  a  binary code file into memory and
       returns the addresses of two procedures within that file, if  they  are
       defined.	 The  appropriate function for the filesystem to which pathPtr
       belongs will be called. If that	filesystem  does  not  implement  this
       function	 (most virtual filesystems will not, because of OS limitations
       in dynamically loading binary code), Tcl will attempt to copy the  file
       to  a  temporary directory and load that temporary file.	 Tcl_FSUnload‐ │
       File reverses the operation, asking for the library  indicated  by  the │
       loadHandle  to  be removed from the process. Note that, unlike with the │
       unload command, this does not give the library any opportunity to clean │
       up.

       Both  the  above functions return a standard Tcl completion code. If an
       error occurs, an error message is left in the interp's result.

       The token provided via the variable indicated by loadHandlePtr  may  be │
       used with Tcl_FindSymbol.

       Tcl_FSMatchInDirectory  is used by the globbing code to search a direc‐
       tory for all files which match a given pattern. The  appropriate	 func‐
       tion for the filesystem to which pathPtr belongs will be called.

       The  return  value is a standard Tcl result indicating whether an error
       occurred in globbing. Error  messages  are  placed  in  interp  (unless
       interp  is  NULL, which is allowed), but good results are placed in the
       resultPtr given.

       Note that the glob code implements recursive  patterns  internally,  so
       this  function  will  only ever be passed simple patterns, which can be
       matched using the logic of string match. To handle recursion, Tcl  will
       call  this  function  frequently	 asking	 only  for  directories	 to be
       returned. A special case of being called with a NULL pattern  indicates
       that the path needs to be checked only for the correct type.

       Tcl_FSLink  replaces the library version of readlink, and extends it to
       support the  creation  of  links.  The  appropriate  function  for  the
       filesystem to which linkNamePtr belongs will be called.

       If  the toPtr is NULL, a “read link” action is performed. The result is
       a Tcl_Obj specifying  the  contents  of	the  symbolic  link  given  by
       linkNamePtr, or NULL if the link could not be read. The result is owned
       by the caller, which should call Tcl_DecrRefCount when the result is no
       longer  needed.	If  the toPtr is not NULL, Tcl should create a link of
       one of the types passed in in the linkAction flag. This flag is an ORed
       combination   of	  TCL_CREATE_SYMBOLIC_LINK  and	 TCL_CREATE_HARD_LINK.
       Where a choice exists (i.e. more than one flag is passed in),  the  Tcl
       convention  is  to  prefer  symbolic links. When a link is successfully
       created, the return value should be toPtr (which is  therefore  already
       owned by the caller). If unsuccessful, NULL is returned.

       Tcl_FSLstat  fills  the	Tcl_StatBuf structure statPtr with information
       about the specified file. You do not need any access rights to the file
       to  get	this information but you need search rights to all directories
       named in the path  leading  to  the  file.  The	Tcl_StatBuf  structure
       includes	 info regarding device, inode (always 0 on Windows), privilege
       mode, nlink (always 1 on Windows), user id (always 0 on Windows), group
       id  (always 0 on Windows), rdev (same as device on Windows), size, last
       access time, last modification time, and	 last  metadata	 change	 time.
       See PORTABLE STAT RESULT API for a description of how to write portable
       code to allocate and access the Tcl_StatBuf structure.

       If path exists, Tcl_FSLstat returns 0 and the stat structure is	filled
       with data. Otherwise, -1 is returned, and no stat info is given.

       Tcl_FSUtime replaces the library version of utime.

       This  returns 0 on success and -1 on error (as per the utime documenta‐
       tion). If successful, the function will update the “atime” and  “mtime”
       values of the file given.

       Tcl_FSFileAttrsGet   implements	read  access  for  the	hookable  file
       attributes subcommand. The appropriate function for the	filesystem  to
       which pathPtr belongs will be called.

       If  the	result	is TCL_OK, then a value was placed in objPtrRef, which
       will only be temporarily valid (unless Tcl_IncrRefCount is called).

       Tcl_FSFileAttrsSet  implements  write  access  for  the	hookable  file
       attributes  subcommand.	The appropriate function for the filesystem to
       which pathPtr belongs will be called.

       Tcl_FSFileAttrStrings implements part of the hookable  file  attributes
       subcommand.  The appropriate function for the filesystem to which path‐
       Ptr belongs will be called.

       The called procedure may either return an  array	 of  strings,  or  may
       instead	return NULL and place a Tcl list into the given objPtrRef. Tcl
       will take that list and first  increment	 its  reference	 count	before
       using  it.  On completion of that use, Tcl will decrement its reference
       count. Hence if the list should be disposed of by  Tcl  when  done,  it
       should  have  a	reference count of zero, and if the list should not be
       disposed of, the filesystem should ensure it retains a reference	 count
       to the value.

       Tcl_FSAccess checks whether the process would be allowed to read, write
       or test for existence of the file (or other  filesystem	object)	 whose
       name  is pathname. If pathname is a symbolic link on Unix, then permis‐
       sions of the file referred by this symbolic link are tested.

       On success (all requested permissions granted), zero  is	 returned.  On
       error  (at least one bit in mode asked for a permission that is denied,
       or some other error occurred), -1 is returned.

       Tcl_FSStat fills the Tcl_StatBuf	 structure  statPtr  with  information
       about the specified file. You do not need any access rights to the file
       to get this information but you need search rights to  all  directories
       named  in  the  path  leading  to  the  file. The Tcl_StatBuf structure
       includes info regarding device, inode (always 0 on Windows),  privilege
       mode, nlink (always 1 on Windows), user id (always 0 on Windows), group
       id (always 0 on Windows), rdev (same as device on Windows), size,  last
       access  time,  last  modification  time, and last metadata change time.
       See PORTABLE STAT RESULT API for a description of how to write portable
       code to allocate and access the Tcl_StatBuf structure.

       If  path	 exists, Tcl_FSStat returns 0 and the stat structure is filled
       with data. Otherwise, -1 is returned, and no stat info is given.

       Tcl_FSOpenFileChannel opens a file specified by pathPtr and  returns  a
       channel	handle	that  can  be  used to perform input and output on the
       file. This API is modeled after the fopen procedure of the  Unix	 stan‐
       dard  I/O  library.  The syntax and meaning of all arguments is similar
       to those given in the Tcl open command when  opening  a	file.	If  an
       error  occurs  while opening the channel, Tcl_FSOpenFileChannel returns
       NULL and records	 a  POSIX  error  code	that  can  be  retrieved  with
       Tcl_GetErrno.   In addition, if interp is non-NULL, Tcl_FSOpenFileChan‐
       nel leaves an error message in interp's result after any error.

       The newly created channel is not	 registered  in	 the  supplied	inter‐
       preter;	to  register it, use Tcl_RegisterChannel.  If one of the stan‐
       dard channels, stdin, stdout or stderr was previously closed,  the  act
       of  creating  the  new channel also assigns it as a replacement for the
       standard channel.

       Tcl_FSGetCwd replaces the library version of getcwd.

       It returns the Tcl library's current working  directory.	 This  may  be
       different  to  the  native  platform's working directory, which happens
       when the current working directory is not in the native filesystem.

       The result is a pointer to a Tcl_Obj specifying the current  directory,
       or  NULL	 if  the current directory could not be determined. If NULL is
       returned, an error message is left in the interp's result.

       The result already has its reference count incremented for the  caller.
       When  it	 is  no	 longer	 needed, that reference count should be decre‐
       mented. This is needed for thread-safety purposes,  to  allow  multiple
       threads	to  access  this  and  related	functions,  while ensuring the
       results are always valid.

       Tcl_FSChdir replaces the library version of chdir. The path is  normal‐
       ized  and  then	passed	to  the	 filesystem  which  claims it. If that
       filesystem does not implement this function, Tcl	 will  fallback	 to  a
       combination  of	stat  and access to check whether the directory exists
       and has appropriate permissions.

       For results, see chdir documentation. If successful, we keep  a	record
       of   the	  successful  path  in	cwdPathPtr  for	 subsequent  calls  to
       Tcl_FSGetCwd.

       Tcl_FSPathSeparator returns the separator character to be used for most
       specific	 element  of the path specified by pathPtr (i.e. the last part
       of the path).

       The separator is returned as a Tcl_Obj containing a string of length 1.
       If the path is invalid, NULL is returned.

       Tcl_FSJoinPath  takes  the  given  Tcl_Obj,  which must be a valid list
       (which is allowed to have a reference count of zero), and  returns  the
       path  value  given  by considering the first elements elements as valid
       path segments (each path segment may be a complete path, a partial path
       or  just a single possible directory or file name). If any path segment
       is actually an absolute path, then all prior  path  segments  are  dis‐
       carded.	If elements is less than 0, we use the entire list.

       It  is  possible	 that the returned value is actually an element of the
       given list, so the caller should be careful to increment the  reference
       count of the result before freeing the list.

       The  returned  value,  typically with a reference count of zero (but it
       could be shared under some conditions), contains the joined  path.  The
       caller must add a reference count to the value before using it. In par‐
       ticular, the returned value could be an element of the given  list,  so
       freeing the list might free the value prematurely if no reference count
       has been taken.	If the number of elements is zero, then	 the  returned
       value will be an empty-string Tcl_Obj.

       Tcl_FSSplitPath	takes the given Tcl_Obj, which should be a valid path,
       and returns a Tcl list value containing each segment of that path as an
       element.	  It  returns  a list value with a reference count of zero. If
       the passed in lenPtr is non-NULL, the variable it  points  to  will  be
       updated to contain the number of elements in the returned list.

       Tcl_FSEqualPaths	 tests	whether the two paths given represent the same
       filesystem object.  It returns 1 if the paths are equal, and 0 if  they
       are different. If either path is NULL, 0 is always returned.

       Tcl_FSGetNormalizedPath	this  important	 function  attempts to extract
       from the given Tcl_Obj a unique normalized path	representation,	 whose
       string value can be used as a unique identifier for the file.

       It returns the normalized path value, owned by Tcl, or NULL if the path
       was invalid or could otherwise not be successfully converted.   Extrac‐
       tion  of	 absolute,  normalized	paths  is  very efficient (because the
       filesystem operates on these representations internally), although  the
       result  when the filesystem contains numerous symbolic links may not be
       the most user-friendly version of a path. The return value is owned  by
       Tcl  and	 has  a	 lifetime  equivalent to that of the pathPtr passed in
       (unless that is a relative path, in  which  case	 the  normalized  path
       value may be freed any time the cwd changes) - the caller can of course
       increment the reference count if it  wishes  to	maintain  a  copy  for
       longer.

       Tcl_FSJoinToPath takes the given value, which should usually be a valid
       path or NULL, and joins onto it the array of paths segments given.

       Returns a value, typically with reference count of zero (but  it	 could
       be shared under some conditions), containing the joined path. The call‐
       er must add a reference count to the value before using it. If  any  of
       the  values passed into this function (pathPtr or path elements) have a
       reference count of zero, they will be freed when this function returns.

       Tcl_FSConvertToPathType tries to convert the given Tcl_Obj to  a	 valid
       Tcl path type, taking account of the fact that the cwd may have changed
       even if this value is already supposedly	 of  the  correct  type.   The
       filename may begin with “~” (to indicate current user's home directory)
       or “~<user>” (to indicate any user's home directory).

       If the conversion succeeds (i.e. the value is a valid path  in  one  of
       the  current filesystems), then TCL_OK is returned. Otherwise TCL_ERROR
       is returned, and an error message may be left in the interpreter.

       Tcl_FSGetInternalRep extracts the internal representation  of  a	 given
       path  value,  in	 the  given filesystem. If the path value belongs to a
       different filesystem, we return NULL. If the internal representation is
       currently  NULL, we attempt to generate it, by calling the filesystem's
       Tcl_FSCreateInternalRepProc.

       Returns NULL or a valid internal	 path  representation.	This  internal
       representation  is cached, so that repeated calls to this function will
       not require additional conversions.

       Tcl_FSGetTranslatedPath attempts to extract the	translated  path  from
       the given Tcl_Obj.

       If  the	translation succeeds (i.e. the value is a valid path), then it
       is returned. Otherwise NULL will be returned, and an error message  may
       be  left	 in the interpreter. A “translated” path is one which contains
       no “~” or “~user” sequences (these have been expanded to their  current
       representation  in  the filesystem). The value returned is owned by the
       caller, which must store it or call Tcl_DecrRefCount to	ensure	memory
       is  freed.  This function is of little practical use, and Tcl_FSGetNor‐
       malizedPath or Tcl_FSGetNativePath are usually better functions to  use
       for most purposes.

       Tcl_FSGetTranslatedStringPath does the same as Tcl_FSGetTranslatedPath,
       but returns a character string or NULL.	The string returned is dynami‐
       cally  allocated	 and  owned by the caller, which must store it or call
       ckfree  to  ensure  it  is  freed.  Again,  Tcl_FSGetNormalizedPath  or
       Tcl_FSGetNativePath  are	 usually better functions to use for most pur‐
       poses.

       Tcl_FSNewNativePath performs something like the reverse	of  the	 usual
       obj->path->nativerep  conversions.  If  some  code  retrieves a path in
       native form (from, e.g. readlink or a native dialog), and that path  is
       to be used at the Tcl level, then calling this function is an efficient
       way of creating the appropriate path value type.

       The resulting value is a pure “path” value, which will only  receive  a
       UTF-8 string representation if that is required by some Tcl code.

       Tcl_FSGetNativePath  is	for use by the Win/Unix native filesystems, so
       that they can easily retrieve the native (char* or TCHAR*)  representa‐
       tion  of	 a  path.  This	 function  is  a  convenience  wrapper	around
       Tcl_FSGetInternalRep. It may be desirable in the future	to  have  non-
       string-based  native  representations (for example, on MacOSX, a repre‐
       sentation using a fileSpec of FSRef structure would  probably  be  more
       efficient).  On	Windows	 a full Unicode representation would allow for
       paths of unlimited length. Currently the	 representation	 is  simply  a
       character  string  which may contain either the relative path or a com‐
       plete, absolute normalized path in the native encoding (complex	condi‐
       tions dictate which of these will be provided, so neither can be relied
       upon, unless the path is known to be absolute). If you  need  a	native
       path which must be absolute, then you should ask for the native version
       of a normalized path. If for some reason a non-absolute, non-normalized
       version	of  the	 path  is  needed, that must be constructed separately
       (e.g. using Tcl_FSGetTranslatedPath).

       The native representation is cached so  that  repeated  calls  to  this
       function	 will  not require additional conversions. The return value is
       owned by Tcl and has a lifetime	equivalent  to	that  of  the  pathPtr
       passed  in  (unless  that  is a relative path, in which case the native
       representation may be freed any time the cwd changes).

       Tcl_FSFileSystemInfo returns a list of two elements. The first  element
       is  the	name  of  the  filesystem  (e.g.   “native”,  “vfs”, “zip”, or
       “prowrap”, perhaps), and the second is the particular type of the given
       path within that filesystem (which is filesystem dependent). The second
       element may be empty if the filesystem does not provide a further cate‐
       gorization of files.

       A  valid	 list  value  is returned, unless the path value is not recog‐
       nized, when NULL will be returned.

       Tcl_FSGetFileSystemForPath returns  a  pointer  to  the	Tcl_Filesystem
       which accepts this path as valid.

       If no filesystem will accept the path, NULL is returned.

       Tcl_FSGetPathType  determines whether the given path is relative to the
       current directory, relative to the current volume, or absolute.

       It   returns   one   of	 TCL_PATH_ABSOLUTE,   TCL_PATH_RELATIVE,    or
       TCL_PATH_VOLUME_RELATIVE

   PORTABLE STAT RESULT API
       Tcl_AllocStatBuf	 allocates a Tcl_StatBuf on the system heap (which may
       be deallocated by being passed to ckfree). This	allows	extensions  to
       invoke  Tcl_FSStat  and Tcl_FSLstat without being dependent on the size
       of the buffer. That in turn depends on the flags used to build Tcl.

       The portable fields of a Tcl_StatBuf may be read	 using	the  following │
       functions,  each	 of which returns the value of the corresponding field │
       listed in the table below. Note that on some  platforms	there  may  be │
       other fields in the Tcl_StatBuf as it is an alias for a suitable system │
       structure, but only the portable ones are made available here. See your │
       system  documentation  for  a full description of these fields.	Access │
       Function			   Field				       │
	Tcl_GetFSDeviceFromStat		   st_dev			       │
	Tcl_GetFSInodeFromStat		   st_ino			       │
	Tcl_GetModeFromStat		   st_mode			       │
	Tcl_GetLinkCountFromStat	   st_nlink			       │
	Tcl_GetUserIdFromStat		   st_uid			       │
	Tcl_GetGroupIdFromStat		   st_gid			       │
	Tcl_GetDeviceTypeFromStat	   st_rdev			       │
	Tcl_GetAccessTimeFromStat	   st_atime			       │
	Tcl_GetModificationTimeFromStat	   st_mtime			       │
	Tcl_GetChangeTimeFromStat	   st_ctime			       │
	Tcl_GetSizeFromStat		   st_size			       │
	Tcl_GetBlocksFromStat		   st_blocks			       │
	Tcl_GetBlockSizeFromStat	   st_blksize

THE VIRTUAL FILESYSTEM API
       A filesystem provides a Tcl_Filesystem structure that contains pointers
       to  functions  that  implement  the various operations on a filesystem;
       these operations are invoked as needed by the generic layer, which gen‐
       erally occurs through the functions listed above.

       The Tcl_Filesystem structures are manipulated using the following meth‐
       ods.

       Tcl_FSRegister takes  a	pointer	 to  a	filesystem  structure  and  an
       optional	 piece	of data to associated with that filesystem. On calling
       this function, Tcl will attach the filesystem  to  the  list  of	 known
       filesystems,  and it will become fully functional immediately. Tcl does
       not check if the same filesystem is registered multiple times  (and  in
       general that is not a good thing to do). TCL_OK will be returned.

       Tcl_FSUnregister	 removes  the given filesystem structure from the list
       of known filesystems, if it  is	known,	and  returns  TCL_OK.  If  the
       filesystem is not currently registered, TCL_ERROR is returned.

       Tcl_FSData  will	 return	 the  ClientData  associated  with  the	 given
       filesystem, if that filesystem is registered. Otherwise it will	return
       NULL.

       Tcl_FSMountsChanged  is	used  to inform the Tcl's core that the set of
       mount  points  for  the	given  (already	 registered)  filesystem  have
       changed,	 and  that cached file representations may therefore no longer
       be correct.

   THE TCL_FILESYSTEM STRUCTURE
       The Tcl_Filesystem structure contains the following fields:

	      typedef struct Tcl_Filesystem {
		  const char *typeName;
		  int structureLength;
		  Tcl_FSVersion version;
		  Tcl_FSPathInFilesystemProc *pathInFilesystemProc;
		  Tcl_FSDupInternalRepProc *dupInternalRepProc;
		  Tcl_FSFreeInternalRepProc *freeInternalRepProc;
		  Tcl_FSInternalToNormalizedProc *internalToNormalizedProc;
		  Tcl_FSCreateInternalRepProc *createInternalRepProc;
		  Tcl_FSNormalizePathProc *normalizePathProc;
		  Tcl_FSFilesystemPathTypeProc *filesystemPathTypeProc;
		  Tcl_FSFilesystemSeparatorProc *filesystemSeparatorProc;
		  Tcl_FSStatProc *statProc;
		  Tcl_FSAccessProc *accessProc;
		  Tcl_FSOpenFileChannelProc *openFileChannelProc;
		  Tcl_FSMatchInDirectoryProc *matchInDirectoryProc;
		  Tcl_FSUtimeProc *utimeProc;
		  Tcl_FSLinkProc *linkProc;
		  Tcl_FSListVolumesProc *listVolumesProc;
		  Tcl_FSFileAttrStringsProc *fileAttrStringsProc;
		  Tcl_FSFileAttrsGetProc *fileAttrsGetProc;
		  Tcl_FSFileAttrsSetProc *fileAttrsSetProc;
		  Tcl_FSCreateDirectoryProc *createDirectoryProc;
		  Tcl_FSRemoveDirectoryProc *removeDirectoryProc;
		  Tcl_FSDeleteFileProc *deleteFileProc;
		  Tcl_FSCopyFileProc *copyFileProc;
		  Tcl_FSRenameFileProc *renameFileProc;
		  Tcl_FSCopyDirectoryProc *copyDirectoryProc;
		  Tcl_FSLstatProc *lstatProc;
		  Tcl_FSLoadFileProc *loadFileProc;
		  Tcl_FSGetCwdProc *getCwdProc;
		  Tcl_FSChdirProc *chdirProc;
	      } Tcl_Filesystem;

       Except for the first three fields in this structure which contain  sim‐
       ple data elements, all entries contain addresses of functions called by
       the generic filesystem layer to perform the complete range of  filesys‐
       tem related actions.

       The  many  functions in this structure are broken down into three cate‐
       gories: infrastructure functions (almost all of which  must  be	imple‐
       mented), operational functions (which must be implemented if a complete
       filesystem is provided), and efficiency functions (which need  only  be
       implemented  if	they can be done so efficiently, or if they have side-
       effects which are required by the filesystem; Tcl  has  less  efficient
       emulations  it  can fall back on). It is important to note that, in the
       current version of Tcl, most of these fallbacks are only used to handle
       commands initiated in Tcl, not in C. What this means is, that if a file
       rename command is issued in Tcl, and the relevant filesystem(s) do  not
       implement  their Tcl_FSRenameFileProc, Tcl's core will instead fallback
       on a combination of other filesystem functions (it will use Tcl_FSCopy‐
       FileProc followed by Tcl_FSDeleteFileProc, and if Tcl_FSCopyFileProc is
       not implemented there is a further fallback). However, if  a  Tcl_FSRe‐
       nameFileProc command is issued at the C level, no such fallbacks occur.
       This is true except for the last four entries in the  filesystem	 table
       (lstat, load, getcwd and chdir) for which fallbacks do in fact occur at
       the C level.

       Any functions which take path names in Tcl_Obj form take those names in
       UTF-8  form.  The  filesystem infrastructure API is designed to support
       efficient, cached conversion of these UTF-8 paths to other native  rep‐
       resentations.

   EXAMPLE FILESYSTEM DEFINITION
       Here  is	 the filesystem lookup table used by the “vfs” extension which
       allows filesystem actions to be implemented in Tcl.

	      static Tcl_Filesystem vfsFilesystem = {
		  "tclvfs",
		  sizeof(Tcl_Filesystem),
		  TCL_FILESYSTEM_VERSION_1,
		  &VfsPathInFilesystem,
		  &VfsDupInternalRep,
		  &VfsFreeInternalRep,
		  /* No internal to normalized, since we don't create
		   * any pure 'internal' Tcl_Obj path representations */
		  NULL,
		  /* No create native rep function, since we don't use
		   * it and don't choose to support uses of
		   * Tcl_FSNewNativePath */
		  NULL,
		  /* Normalize path isn't needed - we assume paths only
		   * have one representation */
		  NULL,
		  &VfsFilesystemPathType,
		  &VfsFilesystemSeparator,
		  &VfsStat,
		  &VfsAccess,
		  &VfsOpenFileChannel,
		  &VfsMatchInDirectory,
		  &VfsUtime,
		  /* We choose not to support symbolic links inside our
		   * VFS's */
		  NULL,
		  &VfsListVolumes,
		  &VfsFileAttrStrings,
		  &VfsFileAttrsGet,
		  &VfsFileAttrsSet,
		  &VfsCreateDirectory,
		  &VfsRemoveDirectory,
		  &VfsDeleteFile,
		  /* No copy file; use the core fallback mechanism */
		  NULL,
		  /* No rename file; use the core fallback mechanism */
		  NULL,
		  /* No copy directory; use the core fallback mechanism */
		  NULL,
		  /* Core will use stat for lstat */
		  NULL,
		  /* No load; use the core fallback mechanism */
		  NULL,
		  /* We don't need a getcwd or chdir; the core's own
		   * internal value is suitable */
		  NULL,
		  NULL
	      };

FILESYSTEM INFRASTRUCTURE
       These fields contain basic information about the	 filesystem  structure
       and  addresses  of  functions  which are used to associate a particular
       filesystem with a file path, and deal with  the	internal  handling  of
       path  representations, for example copying and freeing such representa‐
       tions.

   TYPENAME
       The typeName field contains a null-terminated  string  that  identifies
       the type of the filesystem implemented, e.g.  “native”, “zip” or “vfs”.

   STRUCTURE LENGTH
       The    structureLength	 field	  is	generally    implemented    as
       sizeof(Tcl_Filesystem), and is there to allow easier  binary  backwards
       compatibility  if  the  size  of	 the structure changes in a future Tcl
       release.

   VERSION
       The version field should be set to TCL_FILESYSTEM_VERSION_1.

   PATHINFILESYSTEMPROC
       The pathInFilesystemProc field contains the address of a function which
       is  called  to  determine  whether  a  given path value belongs to this
       filesystem or not. Tcl will only call the rest of the filesystem	 func‐
       tions  with a path for which this function has returned TCL_OK.	If the
       path does not belong, -1 should be returned (the behavior  of  Tcl  for
       any other return value is not defined). If TCL_OK is returned, then the
       optional clientDataPtr output parameter can be used to return an inter‐
       nal  (filesystem	 specific)  representation  of the path, which will be
       cached inside the path value, and may be retrieved efficiently  by  the
       other filesystem functions. Tcl will simultaneously cache the fact that
       this path belongs to this filesystem. Such caches are invalidated  when
       filesystem  structures are added or removed from Tcl's internal list of
       known filesystems.

	      typedef int Tcl_FSPathInFilesystemProc(
		      Tcl_Obj *pathPtr,
		      ClientData *clientDataPtr);

   DUPINTERNALREPPROC
       This function makes a copy of a path's internal representation, and  is
       called when Tcl needs to duplicate a path value. If NULL, Tcl will sim‐
       ply not copy the internal representation, which may  then  need	to  be
       regenerated later.

	      typedef ClientData Tcl_FSDupInternalRepProc(
		      ClientData clientData);

   FREEINTERNALREPPROC
       Free  the internal representation. This must be implemented if internal
       representations need freeing (i.e. if some memory is allocated when  an
       internal representation is generated), but may otherwise be NULL.

	      typedef void Tcl_FSFreeInternalRepProc(
		      ClientData clientData);

   INTERNALTONORMALIZEDPROC
       Function	 to convert internal representation to a normalized path. Only
       required if the filesystem creates pure path values with no string/path
       representation.	The return value is a Tcl value whose string represen‐
       tation is the normalized path.

	      typedef Tcl_Obj *Tcl_FSInternalToNormalizedProc(
		      ClientData clientData);

   CREATEINTERNALREPPROC
       Function to take a path value, and calculate an internal representation
       for  it, and store that native representation in the value. May be NULL
       if paths have no	 internal  representation,  or	if  the	 Tcl_FSPathIn‐
       FilesystemProc for this filesystem always immediately creates an inter‐
       nal representation for paths it accepts.

	      typedef ClientData Tcl_FSCreateInternalRepProc(
		      Tcl_Obj *pathPtr);

   NORMALIZEPATHPROC
       Function to normalize a path. Should be implemented for all filesystems
       which can have multiple string representations for the same path value.
       In Tcl, every “path” must have a single unique “normalized” string rep‐
       resentation.  Depending	on  the filesystem, there may be more than one
       unnormalized string representation which refers to  that	 path  (e.g. a
       relative	 path,	a path with different character case if the filesystem
       is case insensitive, a path contain a reference	to  a  home  directory
       such  as	 “~”, a path containing symbolic links, etc). If the very last
       component in the path is a symbolic link, it should  not	 be  converted
       into  the  value	 it points to (but its case or other aspects should be
       made unique). All other path components should be converted  from  sym‐
       bolic  links. This one exception is required to agree with Tcl's seman‐
       tics with file delete, file rename, file	 copy  operating  on  symbolic
       links.	This  function may be called with nextCheckpoint either at the
       beginning of the path (i.e. zero), at the end of the path,  or  at  any
       intermediate  file  separator  in  the path. It will never point to any
       other arbitrary position in the path. In the last of  the  three	 valid
       cases,  the implementation can assume that the path up to and including
       the file separator is known and normalized.

	      typedef int Tcl_FSNormalizePathProc(
		      Tcl_Interp *interp,
		      Tcl_Obj *pathPtr,
		      int nextCheckpoint);

FILESYSTEM OPERATIONS
       The fields in this section of the structure contain addresses of	 func‐
       tions  which are called to carry out the basic filesystem operations. A
       filesystem which expects to be used with the complete standard Tcl com‐
       mand  set  must	implement all of these. If some of them are not imple‐
       mented, then certain Tcl commands may  fail  when  operating  on	 paths
       within  that  filesystem. However, in some instances this may be desir‐
       able (for example, a read-only filesystem should not implement the last
       four  functions, and a filesystem which does not support symbolic links
       need not implement the readlink function, etc.  The  Tcl	 core  expects
       filesystems to behave in this way).

   FILESYSTEMPATHTYPEPROC
       Function	 to  determine	the  type of a path in this filesystem. May be
       NULL, in which case no type information will be available to  users  of
       the filesystem. The “type” is used only for informational purposes, and
       should be returned as the string representation of the Tcl_Obj which is
       returned.  A typical return value might be “networked”, “zip” or “ftp”.
       The Tcl_Obj result is owned by the filesystem and so Tcl will increment
       the reference count of that value if it wishes to retain a reference to
       it.

	      typedef Tcl_Obj *Tcl_FSFilesystemPathTypeProc(
		      Tcl_Obj *pathPtr);

   FILESYSTEMSEPARATORPROC
       Function to return the  separator  character(s)	for  this  filesystem.
       This need only be implemented if the filesystem wishes to use a differ‐
       ent separator than the standard string “/”.  Amongst other uses, it  is
       returned	 by  the  file separator command. The return value should be a
       value with reference count of zero.

	      typedef Tcl_Obj *Tcl_FSFilesystemSeparatorProc(
		      Tcl_Obj *pathPtr);

   STATPROC
       Function to process a Tcl_FSStat call. Must be implemented for any rea‐
       sonable filesystem, since many Tcl level commands depend crucially upon
       it (e.g. file atime, file isdirectory, file size, glob).

	      typedef int Tcl_FSStatProc(
		      Tcl_Obj *pathPtr,
		      Tcl_StatBuf *statPtr);

       The Tcl_FSStatProc fills the stat structure  statPtr  with  information
       about the specified file. You do not need any access rights to the file
       to get this information but you need search rights to  all  directories
       named in the path leading to the file. The stat structure includes info
       regarding device, inode (always 0 on Windows),  privilege  mode,	 nlink
       (always	1 on Windows), user id (always 0 on Windows), group id (always
       0 on Windows), rdev (same as device  on	Windows),  size,  last	access
       time, last modification time, and last metadata change time.

       If the file represented by pathPtr exists, the Tcl_FSStatProc returns 0
       and the stat structure is filled with data. Otherwise, -1 is  returned,
       and no stat info is given.

   ACCESSPROC
       Function	 to  process  a Tcl_FSAccess call. Must be implemented for any
       reasonable filesystem, since many Tcl level commands  depend  crucially
       upon it (e.g. file exists, file readable).

	      typedef int Tcl_FSAccessProc(
		      Tcl_Obj *pathPtr,
		      int mode);

       The  Tcl_FSAccessProc  checks  whether  the process would be allowed to
       read, write or test for existence of  the  file	(or  other  filesystem
       object)	whose name is in pathPtr. If the pathname refers to a symbolic
       link, then the permissions of the file referred by this	symbolic  link
       should be tested.

       On  success  (all  requested permissions granted), zero is returned. On
       error (at least one bit in mode asked for a permission that is  denied,
       or some other  error occurred), -1 is returned.

   OPENFILECHANNELPROC
       Function	 to  process a Tcl_FSOpenFileChannel call. Must be implemented
       for any reasonable filesystem, since any operations which require  open
       or  accessing  a	 file's contents will use it (e.g. open, encoding, and
       many Tk commands).

	      typedef Tcl_Channel Tcl_FSOpenFileChannelProc(
		      Tcl_Interp *interp,
		      Tcl_Obj *pathPtr,
		      int mode,
		      int permissions);

       The Tcl_FSOpenFileChannelProc opens a file  specified  by  pathPtr  and
       returns	a  channel handle that can be used to perform input and output
       on the file. This API is modeled after the fopen procedure of the  Unix
       standard	 I/O library. The syntax and meaning of all arguments is simi‐
       lar to those given in the Tcl open command when opening a  file,	 where
       the  mode  argument  is	a  combination	of  the	 POSIX flags O_RDONLY,
       O_WRONLY, etc. If an  error  occurs  while  opening  the	 channel,  the
       Tcl_FSOpenFileChannelProc  returns  NULL and records a POSIX error code
       that can be retrieved with Tcl_GetErrno.	 In  addition,	if  interp  is
       non-NULL,  the  Tcl_FSOpenFileChannelProc  leaves  an  error message in
       interp's result after any error.

       The newly created channel must not be registered in the supplied inter‐
       preter by a Tcl_FSOpenFileChannelProc; that task is up to the caller of
       Tcl_FSOpenFileChannel (if necessary). If one of the standard  channels,
       stdin,  stdout or stderr was previously closed, the act of creating the
       new channel also assigns it as a replacement for the standard channel.

   MATCHINDIRECTORYPROC
       Function to process a Tcl_FSMatchInDirectory call. If not  implemented,
       then  glob  and	recursive  copy	 functionality	will be lacking in the
       filesystem (and this may impact commands like encoding names which  use
       glob functionality internally).

	      typedef int Tcl_FSMatchInDirectoryProc(
		      Tcl_Interp *interp,
		      Tcl_Obj *resultPtr,
		      Tcl_Obj *pathPtr,
		      const char *pattern,
		      Tcl_GlobTypeData *types);

       The  function should return all files or directories (or other filesys‐
       tem objects) which match the given pattern and accord  with  the	 types
       specification  given.  There are two ways in which this function may be
       called. If pattern is NULL, then pathPtr is a full  path	 specification
       of a single file or directory which should be checked for existence and
       correct type. Otherwise, pathPtr is a directory, the contents of	 which
       the function should search for files or directories which have the cor‐
       rect type. In either case, pathPtr can be assumed to be	both  non-NULL
       and non-empty. It is not currently documented whether pathPtr will have
       a file separator at its end of not, so code should be flexible to  both
       possibilities.

       The  return  value is a standard Tcl result indicating whether an error
       occurred in the matching process. Error messages are placed in  interp,
       unless interp in NULL in which case no error message need be generated;
       on a TCL_OK result, results should be  added  to	 the  resultPtr	 value
       given  (which  can  be  assumed	to  be a valid unshared Tcl list). The
       matches added to resultPtr should include  any  path  prefix  given  in
       pathPtr (this usually means they will be absolute path specifications).
       Note that if no matches are  found,  that  simply  leads	 to  an	 empty
       result; errors are only signaled for actual file or filesystem problems
       which may occur during the matching process.

       The Tcl_GlobTypeData structure passed in the types  parameter  contains
       the following fields:

	      typedef struct Tcl_GlobTypeData {
		  /* Corresponds to bcdpfls as in 'find -t' */
		  int type;
		  /* Corresponds to file permissions */
		  int perm;
		  /* Acceptable mac type */
		  Tcl_Obj *macType;
		  /* Acceptable mac creator */
		  Tcl_Obj *macCreator;
	      } Tcl_GlobTypeData;

       There are two specific cases which it is important to handle correctly,
       both when types is non-NULL. The two  cases  are	 when  types->types  &
       TCL_GLOB_TYPE_DIR  or  types->types & TCL_GLOB_TYPE_MOUNT are true (and
       in particular when the other flags are false). In the  first  of	 these
       cases,  the function must list the contained directories. Tcl uses this
       to implement recursive globbing, so it  is  critical  that  filesystems
       implement  directory  matching correctly. In the second of these cases,
       with TCL_GLOB_TYPE_MOUNT, the filesystem must  list  the	 mount	points
       which  lie within the given pathPtr (and in this case, pathPtr need not
       lie within the same filesystem - different to all other cases in	 which
       this  function  is  called).  Support for this is critical if Tcl is to
       have seamless transitions between from one filesystem to another.

   UTIMEPROC
       Function to process a Tcl_FSUtime call. Required to allow setting  (not
       reading)	 of  times  with  file	mtime, file atime and the open-r/open-
       w/fcopy implementation of file copy.

	      typedef int Tcl_FSUtimeProc(
		      Tcl_Obj *pathPtr,
		      struct utimbuf *tval);

       The access and modification times of  the  file	specified  by  pathPtr
       should be changed to the values given in the tval structure.

       The return value should be 0 on success and -1 on an error, as with the
       system utime.

   LINKPROC
       Function to process a Tcl_FSLink call. Should be	 implemented  only  if
       the filesystem supports links, and may otherwise be NULL.

	      typedef Tcl_Obj *Tcl_FSLinkProc(
		      Tcl_Obj *linkNamePtr,
		      Tcl_Obj *toPtr,
		      int linkAction);

       If toPtr is NULL, the function is being asked to read the contents of a
       link. The result is a Tcl_Obj specifying the contents of the link given
       by  linkNamePtr,	 or  NULL if the link could not be read. The result is
       owned by the caller (and should therefore have  its  ref	 count	incre‐
       mented before being returned). Any callers should call Tcl_DecrRefCount
       on this result when it is no longer needed.  If toPtr is not NULL,  the
       function	 should	 attempt  to  create  a link.  The result in this case
       should be toPtr if the link was successful and NULL otherwise. In  this
       case  the  result  is  not owned by the caller (i.e. no reference count
       manipulations on either end are	needed).  See  the  documentation  for
       Tcl_FSLink for the correct interpretation of the linkAction flags.

   LISTVOLUMESPROC
       Function	 to  list  any	filesystem  volumes  added by this filesystem.
       Should be implemented only if the filesystem adds volumes at  the  head
       of the filesystem, so that they can be returned by file volumes.

	      typedef Tcl_Obj *Tcl_FSListVolumesProc(void);

       The  result  should  be	a list of volumes added by this filesystem, or
       NULL (or an empty list) if no volumes are provided. The result value is
       considered  to  be  owned  by  the  filesystem (not by Tcl's core), but
       should be given a reference count for Tcl. Tcl will use the contents of
       the  list and then decrement that reference count. This allows filesys‐
       tems to choose whether they actually want to retain a “master list”  of
       volumes	or  not (if not, they generate the list on the fly and pass it
       to Tcl with a reference count of 1 and then forget about the  list,  if
       yes,  then  they	 simply	 increment the reference count of their master
       list and pass it to Tcl which will copy the contents and then decrement
       the count back to where it was).

       Therefore, Tcl considers return values from this proc to be read-only.

   FILEATTRSTRINGSPROC
       Function	 to  list  all	attribute  strings  which  are	valid for this
       filesystem. If not implemented the filesystem will not support the file
       attributes  command. This allows arbitrary additional information to be
       attached to files in the filesystem. If it is not implemented, there is
       no need to implement the get and set methods.

	      typedef const char *const *Tcl_FSFileAttrStringsProc(
		      Tcl_Obj *pathPtr,
		      Tcl_Obj **objPtrRef);

       The  called  function  may  either  return  an array of strings, or may
       instead return NULL and place a Tcl list into the given objPtrRef.  Tcl
       will  take  that	 list  and  first increment its reference count before
       using it.  On completion of that use, Tcl will decrement its  reference
       count.  Hence  if  the  list should be disposed of by Tcl when done, it
       should have a reference count of zero, and if the list  should  not  be
       disposed	 of,  the  filesystem  should ensure it returns a value with a
       reference count of at least one.

   FILEATTRSGETPROC
       Function to process a Tcl_FSFileAttrsGet call, used by file attributes.

	      typedef int Tcl_FSFileAttrsGetProc(
		      Tcl_Interp *interp,
		      int index,
		      Tcl_Obj *pathPtr,
		      Tcl_Obj **objPtrRef);

       Returns a standard Tcl return  code.  The  attribute  value  retrieved,
       which  corresponds  to the index'th element in the list returned by the
       Tcl_FSFileAttrStringsProc, is a Tcl_Obj placed in objPtrRef (if	TCL_OK
       was  returned)  and is likely to have a reference count of zero. Either
       way we must  either  store  it  somewhere  (e.g. the  Tcl  result),  or
       Incr/Decr its reference count to ensure it is properly freed.

   FILEATTRSSETPROC
       Function to process a Tcl_FSFileAttrsSet call, used by file attributes.
       If the filesystem is read-only, there is no need to implement this.

	      typedef int Tcl_FSFileAttrsSetProc(
		      Tcl_Interp *interp,
		      int index,
		      Tcl_Obj *pathPtr,
		      Tcl_Obj *objPtr);

       The attribute value of the index'th element in the list returned by the
       Tcl_FSFileAttrStringsProc should be set to the objPtr given.

   CREATEDIRECTORYPROC
       Function to process a Tcl_FSCreateDirectory call. Should be implemented
       unless the FS is read-only.

	      typedef int Tcl_FSCreateDirectoryProc(
		      Tcl_Obj *pathPtr);

       The return value is a standard Tcl result indicating whether  an	 error
       occurred	 in  the  process.  If successful, a new directory should have
       been added to the filesystem in the location specified by pathPtr.

   REMOVEDIRECTORYPROC
       Function to process a Tcl_FSRemoveDirectory call. Should be implemented
       unless the FS is read-only.

	      typedef int Tcl_FSRemoveDirectoryProc(
		      Tcl_Obj *pathPtr,
		      int recursive,
		      Tcl_Obj **errorPtr);

       The  return  value is a standard Tcl result indicating whether an error
       occurred in the process. If  successful,	 the  directory	 specified  by
       pathPtr	should have been removed from the filesystem. If the recursive
       flag is given, then a non-empty directory  should  be  deleted  without
       error. If this flag is not given, then and the directory is non-empty a
       POSIX “EEXIST” error should be signaled. If an error  does  occur,  the
       name  of	 the file or directory which caused the error should be placed
       in errorPtr.

   DELETEFILEPROC
       Function to process a  Tcl_FSDeleteFile	call.  Should  be  implemented
       unless the FS is read-only.

	      typedef int Tcl_FSDeleteFileProc(
		      Tcl_Obj *pathPtr);

       The  return  value is a standard Tcl result indicating whether an error
       occurred in the process. If successful, the file specified  by  pathPtr
       should  have  been  removed  from  the  filesystem.  Note  that, if the
       filesystem supports symbolic links, Tcl will always call this  function
       and  not	 Tcl_FSRemoveDirectoryProc when needed to delete them (even if
       they are symbolic links to directories).

FILESYSTEM EFFICIENCY
       These functions need not be implemented	for  a	particular  filesystem
       because	the  core  has	a  fallback implementation available. See each
       individual description for the consequences of leaving the field NULL.

   LSTATPROC
       Function to process a Tcl_FSLstat call. If not  implemented,  Tcl  will
       attempt	to  use	 the statProc defined above instead. Therefore it need
       only be implemented if a filesystem can differentiate between stat  and
       lstat calls.

	      typedef int Tcl_FSLstatProc(
		      Tcl_Obj *pathPtr,
		      Tcl_StatBuf *statPtr);

       The  behavior  of  this	function  is  very  similar  to	 that  of  the
       Tcl_FSStatProc defined above, except that if it is applied  to  a  sym‐
       bolic link, it returns information about the link, not about the target
       file.

   COPYFILEPROC
       Function to process a Tcl_FSCopyFile call. If not implemented Tcl  will
       fall  back  on open-r, open-w and fcopy as a copying mechanism.	There‐
       fore it need only be implemented if the	filesystem  can	 perform  that
       action more efficiently.

	      typedef int Tcl_FSCopyFileProc(
		      Tcl_Obj *srcPathPtr,
		      Tcl_Obj *destPathPtr);

       The  return  value is a standard Tcl result indicating whether an error
       occurred in the copying process. Note that, destPathPtr is the name  of
       the  file  which	 should become the copy of srcPathPtr. It is never the
       name of a directory into which srcPathPtr  could	 be  copied  (i.e. the
       function is much simpler than the Tcl level file copy subcommand). Note
       that, if the filesystem supports symbolic links, Tcl will  always  call
       this  function and not copyDirectoryProc when needed to copy them (even
       if they are symbolic links to directories). Finally, if the  filesystem
       determines  it  cannot support the file copy action, calling Tcl_SetEr‐
       rno(EXDEV) and returning a non-TCL_OK result will tell Tcl to  use  its
       standard fallback mechanisms.

   RENAMEFILEPROC
       Function	 to  process  a Tcl_FSRenameFile call. If not implemented, Tcl
       will fall back on a copy and delete mechanism. Therefore it  need  only
       be  implemented	if  the	 filesystem can perform that action more effi‐
       ciently.

	      typedef int Tcl_FSRenameFileProc(
		      Tcl_Obj *srcPathPtr,
		      Tcl_Obj *destPathPtr);

       The return value is a standard Tcl result indicating whether  an	 error
       occurred	 in the renaming process. If the filesystem determines it can‐
       not support the file rename  action,  calling  Tcl_SetErrno(EXDEV)  and
       returning  a  non-TCL_OK result will tell Tcl to use its standard fall‐
       back mechanisms.

   COPYDIRECTORYPROC
       Function to process a Tcl_FSCopyDirectory call. If not implemented, Tcl
       will  fall  back on a recursive file mkdir, file copy mechanism. There‐
       fore it need only be implemented if the	filesystem  can	 perform  that
       action more efficiently.

	      typedef int Tcl_FSCopyDirectoryProc(
		      Tcl_Obj *srcPathPtr,
		      Tcl_Obj *destPathPtr,
		      Tcl_Obj **errorPtr);

       The  return  value is a standard Tcl result indicating whether an error
       occurred in the copying process. If an error does occur,	 the  name  of
       the  file  or  directory	 which	caused	the  error should be placed in
       errorPtr. Note that, destPathPtr is  the	 name  of  the	directory-name
       which  should become the mirror-image of srcPathPtr. It is not the name
       of a directory into which srcPathPtr should be copied  (i.e. the	 func‐
       tion is much simpler than the Tcl level file copy subcommand). Finally,
       if the filesystem determines  it	 cannot	 support  the  directory  copy
       action,	calling	 Tcl_SetErrno(EXDEV) and returning a non-TCL_OK result
       will tell Tcl to use its standard fallback mechanisms.

   LOADFILEPROC
       Function to process a Tcl_FSLoadFile call. If not implemented, Tcl will
       fall back on a copy to native-temp followed by a Tcl_FSLoadFile on that
       temporary copy. Therefore it need only be implemented if the filesystem
       can  load  code	directly,  or  it  can be implemented simply to return
       TCL_ERROR to disable load functionality in this filesystem entirely.

	      typedef int Tcl_FSLoadFileProc(
		      Tcl_Interp *interp,
		      Tcl_Obj *pathPtr,
		      Tcl_LoadHandle *handlePtr,
		      Tcl_FSUnloadFileProc *unloadProcPtr);

       Returns a standard Tcl completion code. If an error  occurs,  an	 error
       message	is left in the interp's result. The function dynamically loads
       a binary code file into memory. On a  successful	 load,	the  handlePtr
       should  be filled with a token for the dynamically loaded file, and the
       unloadProcPtr should be filled in with the address of a procedure.  The
       unload  procedure  will	be called with the given Tcl_LoadHandle as its
       only parameter when Tcl needs to unload the file. For example, for  the
       native  filesystem,  the	 Tcl_LoadHandle	 returned is currently a token
       which can be used in the private TclpFindSymbol to access functions  in
       the  new	 code. Each filesystem is free to define the Tcl_LoadHandle as
       it requires. Finally, if the filesystem determines  it  cannot  support
       the  file load action, calling Tcl_SetErrno(EXDEV) and returning a non-
       TCL_OK result will tell Tcl to use its standard fallback mechanisms.

   UNLOADFILEPROC
       Function to unload a previously successfully loaded file. If  load  was
       implemented,  then  this	 should	 also  be implemented, if there is any
       cleanup action required.

	      typedef void Tcl_FSUnloadFileProc(
		      Tcl_LoadHandle loadHandle);

   GETCWDPROC
       Function to process a Tcl_FSGetCwd  call.  Most	filesystems  need  not
       implement  this.	 It  will  usually  only  be called once, if getcwd is
       called before chdir. May be NULL.

	      typedef Tcl_Obj *Tcl_FSGetCwdProc(
		      Tcl_Interp *interp);

       If the filesystem supports a native notion of a current working	direc‐
       tory  (which  might  perhaps  change independent of Tcl), this function
       should return that cwd as the result, or NULL if the current  directory
       could  not  be determined (e.g. the user does not have appropriate per‐
       missions on the cwd directory). If NULL is returned, an	error  message
       is left in the interp's result.

   CHDIRPROC
       Function to process a Tcl_FSChdir call. If filesystems do not implement
       this, it will be emulated by a series of directory access checks.  Oth‐
       erwise,	virtual	 filesystems  which  do implement it need only respond
       with a positive return result if the pathPtr  is	 a  valid,  accessible
       directory in their filesystem. They need not remember the result, since
       that will be automatically remembered for use  by  Tcl_FSGetCwd.	  Real
       filesystems  should carry out the correct action (i.e. call the correct
       system chdir API).

	      typedef int Tcl_FSChdirProc(
		      Tcl_Obj *pathPtr);

       The Tcl_FSChdirProc changes the applications current working  directory
       to  the value specified in pathPtr. The function returns -1 on error or
       0 on success.

SEE ALSO
       cd(n),  file(n),	 filename(n),  load(n),	 open(n),  pwd(n),  source(n),
       unload(n)

KEYWORDS
       stat, access, filesystem, vfs, virtual filesystem

Tcl				      8.4			 Filesystem(3)
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