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You can specify an argument for the --file=archive-name (-f archive-name) option whenever you use tar; this option determines the name of the archive file that tar will work on.
If you don't specify this argument, then tar will examine the environment variable TAPE. If it is set, its value will be used as the archive name. Otherwise, tar will use the default archive, determined at the compile time. Usually it is standard output or some physical tape drive attached to your machine (you can verify what the default is by running tar --show-defaults, see defaults). If there is no tape drive attached, or the default is not meaningful, then tar will print an error message. The error message might look roughly like one of the following:
tar: can't open /dev/rmt8 : No such device or address
tar: can't open /dev/rsmt0 : I/O error
To avoid confusion, we recommend that you always specify an archive file name by using --file=archive-name (-f archive-name) when writing your tar commands. For more information on using the --file=archive-name (-f archive-name) option, see file.