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ActiveTcl User Guide
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[ Main table Of Contents | TclVFS Table Of Contents | TclVFS Index ]
vfs(n) 1.0 "Tcl-level Virtual Filesystems"
vfs - Filesystem management in Tcl
package require Tcl 8.4
package require vfs ?1.2.1?
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 section "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, ...), 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).
Because all of Tcl's filesystem activity passes through a single
layer, every operation can be intercepted. 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 registration 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.
- 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 represented 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
executed.
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 interpreters).
- 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 evaluated.
- 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.
The code of the package vfs has only a few
limitations.
- One subtlety one has to be aware of is that mixing
case-(in)sensitive filesystems and application 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 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.
- 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.
- The public C-API filesystem function
Tcl_FSMatchInDirectory is given a variety of type
information 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.
vfs-filesystems , vfs-fsapi
file , filesystem , vfs
Copyright © 2001-2003 Vince Darley
<vincentdarley@users.sourceforge.net>
Copyright © 2003 Andreas Kupries
<andreas_kupries@users.sourceforge.net>