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Old options are single letters not preceeded by any dash at all, and appearing only in the position immediately following the `tar' keyword in the command, after some white space. The letter of an old option is exactly the same letter as the corresponding short option. For example, the old option `t' is the same as the short option `-t', and consequently, the same as long option `--list' (`-t').
As far as we know, all tar programs, GNU and non-GNU, support
old options. GNU tar supports them not only for historical
reasons, but also because many people are used to them.
All old options should be written as a single argument, without
separating spaces, by lumping together all letters specifying these
options. This set of letters should be the first to appear on the
command line, after the tar program name; old options cannot
appear anywhere else. Then, for any old option required an argument,
the argument should follow on the command line. Arguments to the
options should appear in the same order as the letters to which
they correspond. The tar command synopsis might be rewritten:
tar letter... [argument]... [option]... [name]...
when old options are being used.
This command syntax is useful because it lets you type the single letter
forms of the operation and options as a single argument to tar,
without writing preceding `-'s or inserting spaces between letters.
`tar cv' or `tar -cv' are equivalent to `tar -c -v'.
For compatibility with Unix tar, the first argument can
contain an option letter (or a cluster of option letters) not
introduced by a dash; for example, `tar cv' specifies the option
`-v' in addition to the command `-c'. When options that
need arguments are given together with the command, all the associated
arguments follow, in the same order as the options. Thus, the example
above could also be written in the old style as follows:
tar cvbf 20 /dev/rmt0
Here `20' is the argument of `-b' and `/dev/rmt0' is the argument of `-f'.
On the other hand, this old style syntax makes it difficult to match option letters with their corresponding arguments, and is often confusing. In the command `tar cvbf 20 /dev/rmt0', for example, `20' is the argument for `-b', `/dev/rmt0' is the argument for `-f', and `-v' does not have a corresponding argument. Even using short options like in `tar -c -v -b 20 -f /dev/rmt0' is clearer, putting all arguments next to the option they pertain to.
If you want to reorder the letters in the old option argument, be sure to appropriately reorder any corresponding argument.
This old way of writing tar options can surprise even experienced
users. For example, the two commands:
tar cfz archive.tar.gz file tar -cfz archive.tar.gz file
are quite different. The first example uses `archive.tar.gz' as
the value for option `f' and recognizes the option `z'. The
second example, however, uses `z' as the value for option
`f'---probably not what was intended. (I find it quite inelegant
that getopt batches the remaining `z' as the value for
`f'. I think that clarity dictates that clustering of option
letters, when some require arguments, should be diagnosed and
disallowed. But compatibility with traditional systems dictates it.)
This second example could be corrected in many ways, among which:
tar -czf archive.tar.gz file tar -cf archive.tar.gz -z file tar cf archive.tar.gz -z file
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