@UNREVISED
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 preferrable to him/her.
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>'.
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 overriden this by defining the environment
variable RSH at installation time.
tar to write a multi-volume archive--one
that may be larger than will fit on the medium used to hold it.
See section Archives Longer than One Tape or Disk.
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