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(tar.info)Device

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Device Selection and Switching
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`-f [HOSTNAME:]FILE'
`--file=[HOSTNAME:]FILE'
     Use archive file or device FILE on HOSTNAME.

   This option is used to specify the file name of the archive `tar'
works on.

   If the file name is `-', `tar' reads the archive from standard input
(when listing or extracting), or writes it to standard output (when
creating).  If the `-' file name is given when updating an archive,
`tar' will read the original archive from its standard input, and will
write the entire new archive to its standard output.

   If the file name contains a `:', it is interpreted as `hostname:file
name'.  If the HOSTNAME contains an "at" sign (`@'), it is treated as
`user@hostname:file name'.  In either case, `tar' will invoke the
command `rsh' (or `remsh') to start up an `/etc/rmt' on the remote
machine.  If you give an alternate login name, it will be given to the
`rsh'.  Naturally, the remote machine must have an executable
`/etc/rmt'.  This program is free software from the University of
California, and a copy of the source code can be found with the sources
for `tar'; it's compiled and installed by default.

   If this option is not given, but the environment variable `TAPE' is
set, its value is used; otherwise, old versions of `tar' used a default
archive name (which was picked when `tar' was compiled).  The default
is normally set up to be the "first" tape drive or other transportable
I/O medium on the system.

   Starting with version 1.11.5, GNU `tar' uses standard input and
standard output as the default device, and I will not try anymore
supporting automatic device detection at installation time.  This was
failing really in too many cases, it was hopeless.  This is now
completely left to the installer to override standard input and standard
output for default device, if this seems preferable.  Further, I think
_most_ actual usages of `tar' are done with pipes or disks, not really
tapes, cartridges or diskettes.

   Some users think that using standard input and output is running
after trouble.  This could lead to a nasty surprise on your screen if
you forget to specify an output file name--especially if you are going
through a network or terminal server capable of buffering large amounts
of output.  We had so many bug reports in that area of configuring
default tapes automatically, and so many contradicting requests, that
we finally consider the problem to be portably intractable.  We could
of course use something like `/dev/tape' as a default, but this is
_also_ running after various kind of trouble, going from hung processes
to accidental destruction of real tapes.  After having seen all this
mess, using standard input and output as a default really sounds like
the only clean choice left, and a very useful one too.

   GNU `tar' reads and writes archive in records, I suspect this is the
main reason why block devices are preferred over character devices.
Most probably, block devices are more efficient too.  The installer
could also check for `DEFTAPE' in `<sys/mtio.h>'.

`--force-local'
     Archive file is local even if it contains a colon.

`--rsh-command=COMMAND'
     Use remote COMMAND instead of `rsh'.  This option exists so that
     people who use something other than the standard `rsh' (e.g., a
     Kerberized `rsh') can access a remote device.

     When this command is not used, the shell command found when the
     `tar' program was installed is used instead.  This is the first
     found of `/usr/ucb/rsh', `/usr/bin/remsh', `/usr/bin/rsh',
     `/usr/bsd/rsh' or `/usr/bin/nsh'.  The installer may have
     overridden this by defining the environment variable `RSH' _at
     installation time_.

`-[0-7][lmh]'
     Specify drive and density.

`-M'
`--multi-volume'
     Create/list/extract multi-volume archive.

     This option causes `tar' to write a "multi-volume" archive--one
     that may be larger than will fit on the medium used to hold it.
     Note: Multi-Volume Archives.

`-L NUM'
`--tape-length=NUM'
     Change tape after writing NUM x 1024 bytes.

     This option might be useful when your tape drivers do not properly
     detect end of physical tapes.  By being slightly conservative on
     the maximum tape length, you might avoid the problem entirely.

`-F FILE'
`--info-script=FILE'
`--new-volume-script=FILE'
     Execute `file' at end of each tape.  If `file' exits with nonzero
     status, exit.  This implies `--multi-volume' (`-M').