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vfs(n)                                                                                                vfs(n)



____________________________________________________________________________________________________________

NAME
       vfs - Filesystem management in Tcl

SYNOPSIS
       package require Tcl  8.4

       package require vfs  ?1.2.1?

       vfs::filesystem mount ?-volume? path command

       vfs::filesystem unmount path

       vfs::filesystem info ?path?

       vfs::filesystem fullynormalize path

       vfs::filesystem posixerror int

       vfs::filesystem internalerror command

____________________________________________________________________________________________________________

DESCRIPTION
       The package vfs provides commands to query, mount and unmount virtual filesystems implemented in Tcl.
       This is further facilitated through the provison of helper commands in a tcl script library. See sec-tion section
       tion "HANDLER ENVIRONMENT" of vfs-fsapi for more information.

       Once  a  virtual  filesystem  is in place, the standard Tcl commands, like file, glob, cd, pwd, open,
       including all their C APIs in the Tcl library (e.g.   Tcl_FSOpenFileChannel,  Tcl_FSMatchInDirectory,
       extensions  such  as  Tk  which  may  open  or  read files will also transparently access the virtual
       filesystem).

       Because all of Tcl's filesystem activity passes through a single layer, every operation can be inter-cepted. intercepted.
       cepted.  This  package does just that.  This is also quite different from simply overloading the file
       command in Tcl.  We are actually providing replacements for C commands like access,  stat,  etc.   By
       implementing  a  small number of low-level commands we ensure that all commands at higher levels will
       function irrespective of what is going on inside the filesystem layer.

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

       To  access  this  package  use the command package require vfs.  This automatically registers the vfs
       hooks into Tcl's filesystem and provides the command vfs::filesystem. The latter allows the registra-tion registration
       tion  of actual virtual filesystems. More in the upcoming section API.  The hooks will not be removed
       until Tcl exits. If desired, control over this could be exposed to Tcl in  the  future.   By  and  in
       itself the command above will have no further effect. Only after filesystem implementations have been
       registered and filesystems using them been mounted filesystem commands will actually be  intercepted,
       and handled by the Tcl code of the mounted virtual filesystem.

API
       vfs::filesystem mount ?-volume? path command
              Mounts  a  virtual  filesystem  at  path,  making it useable. After completion of the call any
              access to a subdirectory of path will be handled by that filesystem. The filesystem is  repre-sented represented
              sented  here  by  the command prefix which will be executed whenever an operation on a file or
              directory within path has to be performed.

              Whether the command is implemented in C or Tcl is of no relevance as long as it adheres to the
              API specified in vfs-fsapi and is present in the interpreter where the mount operation is exe-cuted. executed.
              cuted.

              If the option -volume is specified the new mount point is also registered with Tcl  as  a  new
              volume  and will therefore from then on appear in the output of the command file volumes. This
              is useful (and required for reasonable operation) for mounts like ftp://.  It  should  not  be
              used for paths mounted inside the native filesystem.

              The  new  filesystem  mounts  will  be observed immediately in all interpreters in the current
              process.  If the interpreter is later deleted, all mounts which are intercepted by it will  be
              automatically removed (and will therefore affect the view of the filesystem seen by all inter-preters). interpreters).
              preters).

       vfs::filesystem unmount path
              This unmounts the virtual filesystem which was mounted at path.  An  error  is  thrown  if  no
              filesystem  was  mounted  there.   After the completion of the operation the filesystem is not
              visible anymore, and any previous filesystem accessible through this path  becomes  accessible
              again.

       vfs::filesystem info ?path?
              A  list  of  all  filesystems mounted in all interpreters is returned, if no path argument was
              specified.  Else the filesystem responsible for that path is examined and the  command  prefix
              used  to  handle  all  filesystem operations returned.  An error is thrown if no filesystem is
              mounted for that path.

              There is currently no facility for examining in which interpreter each command will be  evalu-ated. evaluated.
              ated.

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

       vfs::filesystem posixerror int
              This command can be called by filesystem implementations during the execution of a  filesystem
              operation to signal the posix error code of a failure. See also vfs-fsapi.

       vfs::filesystem internalerror command
              When  used  the  specified command is registerd as the command to trap and report any internal
              errors thrown by filesystem implementations.


LIMITATIONS
       The code of the package vfs has only a few limitations.


       [1]    One subtlety one has to be aware of is that mixing case-(in)sensitive filesystems and applica-tion application
              tion code may yield unexpected results.

              For  example mounting a case-sensitive virtual filesystem into a case-insensitive system (like
              the standard Windows or MacOS filesystems) and then using this  with  code  relying  on  case-insensitivity caseinsensitivity
              insensitivity problems will appear when accessing the virtual filesystem.

              Note  that  application code relying on case-insensitivity will not under Unix either, i.e. is
              inherently non-portable, and should be fixed.

       [2]    The C-API's for link and lstat are currently not exposed to the Tcl level. This may be done in
              the  future to allow virtual filesystems implemented in Tcl to support the reading and writing
              of links.

       [3]    The public C-API filesystem function Tcl_FSMatchInDirectory is given a variety of type  infor-mation information
              mation  in  a  Tcl_GlobTypeData structure.  Currently only the type field of said strcuture is
              exposed to the tcl-level. Fields like permissions and MacOS type/creator are ignored.


SEE ALSO
       vfs-filesystems, vfs-fsapi

KEYWORDS
       file, filesystem, vfs

COPYRIGHT
       Copyright (c) 2001-2003 Vince Darley <vincentdarley@users.sourceforge.net>
       Copyright (c) 2003 Andreas Kupries <andreas_kupries@users.sourceforge.net>




Tcl-level Virtual Filesystems                        1.0                                              vfs(n)