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vfs(n)			 Tcl-only Virtual File Systems			vfs(n)

       ::vfs - Commands	and Procedures to create virtual filesystems

       package require Tcl 8.4

       package require vfs ?1.2.1?

       vfs::filesystem info

       vfs::filesystem mount

       vfs::filesystem unmount

       vfs::accessMode mode

       vfs::matchDirectories types

       vfs::matchFiles types

       vfs::matchCorrectTypes types filelist ?inDir?

       The ::vfs package provides commands to query, mount and unmount virtual
       filesystems, and	provides as Tcl	libraries some facilities for  helping
       the writing of new virtual filesystems in Tcl.  Once a virtual filesys-
       tem is in place,	the standard Tcl file, glob, cd, pwd,  open  commands,
       including all their C APIs in the Tcl library (e.g. Tcl_FSOpenFileChan-
       nel, Tcl_FSMatchInDirectory,...), can be	 used  within  the  filesystem
       (and  indeed,  properly written extensions such as Tk which may open or
       read files will also transparently access the virtual filesystem).  Be-
       cause  all  of  Tcl's FS	activity passes	through	a single layer,	it can
       all be intercepted.  This package does just that.  Notice that this  is
       quite  different	 to overloading	the file command in Tcl.  We are actu-
       ally providing vfs replacements for C commands like access,  stat.   By
       implementing  just  a  handful of commands at this low level, we	ensure
       that all	commands at higher levels function irrespective	of what	is go-
       ing on inside the FS layer.

       Tcl's  filesystem hooks operate on a per-process	basis.	This means ev-
       ery Tcl interpreter in  the  same  process/application  sees  the  same
       filesystem, including any virtual filesystems.

       The  package require vfs	command	should be used to access this library.
       It automatically	registers the vfs hooks	 into  Tcl's  filesystem,  and
       these  will  not	 be  removed until Tcl exits (if desired, control over
       this could be exposed to	Tcl in the future).  However, the vfs  package
       will  at	 that  stage  not have any new filesystems mounted, so it will
       have little effect.  Note that package require  vfs  has	 two  effects.
       First  of  all, when it is issued in any	Tcl interpreter	it will	ensure
       the vfs hooks have been registered with Tcl's core just	once  (and  if
       any  of	those interpreters are later deleted, the vfs hooks will still
       remain registered - they	remain until Tcl exits).  The second effect is
       to  provide the command vfs::filesystem which allows the	interpreter to
       intercept filesystem commands and handle	them with Tcl code in that in-

       There  are  three  somewhat unsupported subcommands of vfs::filesystem,
       fullynormalize path, posixerror int, internalerror ?script?, which  are
       used  to	 normalize a path (including any final symlink), to register a
       posix error code	with a Tcl error, and to trap/report  internal	errors
       in tclvfs implementations respectively.

       vfs::filesystem mount ?-volume? path command
	      To use a virtual filesystem, it must be 'mounted'.  Mounting in-
	      volves declaring to the vfs package that any subdirectories of a
	      given path in the	filesystem should be handled by	the given com-
	      mand which should	be a Tcl command or procedure  in  the	inter-
	      preter  in which the vfs::filesystem is executed.	 If the	?-vol-
	      ume?  flag is given, the given mount point  is  also  registered
	      with  Tcl	as a new volume	(like a	new drive which	will appear in
	      file volumes).  This is useful (and required for reasonable  op-
	      eration)	for  mounts like ftp://.  For paths mounted inside the
	      native filesystem, it should of course not be  given.   The  new
	      filesystem  mounts  will	be  observed immediately in all	inter-
	      preters in the current process.  If  the	interpreter  is	 later
	      deleted, all mounts which	are intercepted	by it will be automat-
	      ically removed (and  will	 therefore  affect  the	 view  of  the
	      filesystem seen by all interpreters).

       vfs::filesystem unmount path
	      This  unmounts  the virtual filesystem which was mounted at path
	      (hence removing it from Tcl's filesystem), or throws an error if
	      no filesystem was	mounted	there.

       vfs::filesystem info ?path?
	      If  no  arguments	are given, this	returns	a list of all filesys-
	      tems mounted (in all  interpreters).   If	 a  path  argument  is
	      given, then the command to be used for that path is returned, or
	      an error is thrown if no vfs is mounted for that path.  There is
	      currently	 no  facility  for examining in	which interpreter each
	      command will be evaluated.

       vfs::filesystem fullynormalize path
	      Performs a full expansion	of path, (as  per  'file  normalize'),
	      but including following any links	in the last element of path.

       The  vfs	 package will intercept	every filesystem operation which falls
       within a	given mount point, and pass the	 operation  on	to  the	 mount
       point's command in the interpreter which	registered it. In general this
       occurs by the C equivalent of an	evaluation like	 this:	eval  $command
       [list $subcmd $root $relative $actualpath] $args.

       Here  subcmd  may  be  any  of  the following: access, createdirectory,
       deletefile, fileattributes,  matchindirectory,  open,  removedirectory,
       stat,  utime.  If  command  takes  appropriate action for each of these
       cases, a	complete, perfect virtual filesystem will be achieved,	indis-
       tinguishable  to	Tcl from the native filesystem.	 (CAVEATS: right now I
       don't expose to Tcl all the permission-related flags of 'glob').

       The remaining arguments specify a file path on which  to	 operate  (all
       commands	 operate  on one of these), and	any additional arguments which
       may be required to carry	out the	action.	 The file path is specified by
       three  arguments:  root is the part of the path which lies outside this
       filesystem's mount point, relative is the part of the path  which  lies
       inside  this  filesytem,	 and actualpath	is the original	(unnormalized)
       name of the path	which was used in  the	current	 command  wherever  it
       originated (in Tcl or C).  For example, if C:/foo/bar/
       is a path in your filesystem, where is	a  zip	archive	 which
       has  been mounted (on top of itself) and	contains xxx/yyy, and the cur-
       rent working directory is inside	xxx, and we evaluate  a	 command  like
       file  exists  yyy, then rootwill	be C:/foo/bar/, relative will
       be xxx/yyy, and actualpath will be yyy. The file	separator between  the
       root and	relative is omitted.

       Note that most filesystem operations will only require the relative ar-
       gument to work correctly, but the other arguments are actually required
       for correct operation of	some subcommands.

       Almost  all of these commands should either return correctly (i.e. with
       a TCL_OK	result at the C	level)	or  they  should  use  vfs::filesystem
       posixerror  to signal the appropriate posix error code.	If a Tcl error
       is thrown, that should be considered a bug, but it will be  interpreted
       as  an  unknown	posix error in the filesystem call.  The exceptions to
       these rules are those filesystem	commands which are able	to  specify  a
       Tcl  error  message  directly:  open  (when  an	interpreter is given),
       matchindirectory	and fileattributes (for	a set or get operation	only).
       These  three  commands are allowed to throw any Tcl error message which
       will be passed along to the caller, or they may	throw  a  posix	 error
       which will be handled appropriately.

       The actual commands are as follows (where r-r-a represents the standard
       argument	triplet	of root, relative and actualpath):

       command access r-r-a mode
	      Return TCL_OK or throw a posix error depending  on  whether  the
	      given  access  mode (which is an integer)	is compatible with the

       command createdirectory r-r-a
	      Create a directory with the given	name.  The command can	assume
	      that  all	 sub-directories  in the path exist and	are valid, and
	      that the actual desired path does	not yet	exist (Tcl takes  care
	      of all of	that for us).

       command deletefile r-r-a
	      Delete the given file.

       command fileattributes r-r-a ?index? ?value?
	      If  neither  index nor value is given, then return a list	of all
	      acceptable attribute names.  If index is given,  but  no	value,
	      then  retrieve  the value	of the index'th	attribute (counting in
	      order over the list returned when	no argument is given) for  the
	      given  file.  If a value is also given then set the index'th at-
	      tribute of the given file	to that	value.

       command matchindirectory	r-r-a pattern types
	      Return the list of files or directories in the given path	(which
	      is  always  the  name of an existing directory), which match the
	      pattern and are compatible with the types	given.	It is very im-
	      portant that the command correctly handle	types requests for di-
	      rectories	only (and files	only), because to handle any  kind  of
	      recursive	 globbing, Tcl will actually generate requests for di-
	      rectory-only matches from	the filesystem.	 See  vfs::matchDirec-
	      tories below for help.

       command open r-r-a mode permissions
	      For  this	command, mode is any of	"r", "w", "a", "w+", "a+".  If
	      the open involves	creating a  file,  then	 permissions  dictates
	      what  modes  to  create  it with.	 If the	open operation was not
	      successful, an error should be thrown.  If the open operation is
	      successful,  the	command	 should	return a list of either	one or
	      two items.  The first item (which	is obligatory) is the name  of
	      the  channel which has been created.  The	second item, if	given,
	      is a Tcl-callback	to be used when	the channel is closed, so that
	      the  vfs	can  clean  up	as appropriate.	 This callback will be
	      evaluated	by Tcl just before the channel is closed.  The channel
	      will  still exist, and all available data	will have been flushed
	      into it.	The callback can, for example, seek to	the  beginning
	      of  the channel, read its	contents and store that	contents else-
	      where (e.g. compressed or	on a remote ftp	site, etc).   The  re-
	      turn code	or any errors returned by the callback are ignored (if
	      the callback wishes to signal an error,  it  must	 do  so	 asyc-
	      nhronously,  with	bgerror, for example), unless the 'internaler-
	      ror' script has been specified, when they	 are  passed  to  that
	      script for further action.

       command removedirectory r-r-a recursive
	      Delete  the  given directory.  recursive is either 0 or 1. If it
	      is 1 then	even if	the directory is non-empty, an attempt	should
	      be  made	to recursively delete it and its contents.  If it is 0
	      and the directory	is non-empty, a	posix error (EEXIST) should be

       command stat r-r-a
	      Return  a	 list  of  even	length containing field-name and value
	      pairs for	the contents of	a stat structure.  The	order  is  not
	      important.   The	option	names are dev (long), ino (long), mode
	      (int), nlink (long), uid (long), gid (long), size	(long),	 atime
	      (long), mtime (long), ctime (long), type (string which is	either
	      "directory" or "file"), where the	type of	each argument is given
	      in  brackets.   The procedure should therefore return with some-
	      thing like return	[list dev 0 type file mtime 1234 ...].

       command utime r-r-a actime mtime
	      Set the access and modification times of the given  file	(these
	      are read with 'stat').

       The  vfslib  provides  a	 number	 of Tcl	procedures which can help with
       writing command procedures to handle the	 above	possibilities.	 These

       vfs::accessMode mode
	      converts	an  integer  access mode to a somewhat more preferable
	      string, any of F X W XW R	RX RW.

       vfs::matchDirectories types
	      Does types want directories included?

       vfs::matchFiles types
	      Does types want files included?

       vfs::matchCorrectTypes types filelist ?inDir?
	      Returns that subset of the filelist (which are  either  absolute
	      paths  or	names of files in inDir) which are compatible with the
	      types given.

       Use something like this	to  debug  problems  in	 your  implementation:
       vfs::filesystem	internalerror  report  ;  proc report {} { puts	stderr
       $::errorInfo }

       There are very few limitations to the vfs code.	One subtlety that  you
       may  encounter is if you	mount a	case-sensitive virtual filesystem into
       a case-insensitive system (e.g. the standard Windows or MacOS  fs)  and
       your  code  relies on case-insensitivity, then it will not run properly
       in the virtual filesystem.  Of course if	your code relies  on  case-in-
       sensitivity,  it	wouldn't run under Tcl on Unix either, so the best so-
       lution is to fix	your code!

       We may add link and lstat commands  in  the  future  to	allow  virtual
       filesystems to support reading and writing links	- this is supported by
       the C API, but has simply not been exposed to Tcl  in  this  extension,

       The  Tcl	 'Tcl_FSMatchInDirectory' function takes a variety of type in-
       formation in a Tcl_GlobTypeData structure.  We  currently  only	expose
       the  'type'  field  from	that structure (so the 'permissions' and MacOS
       type/creator fields are ignored).

       vfs, filesystem,	file

Vfs				     1.2.1				vfs(n)


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