Typically, tar carries out a command without stopping for
further instructions. In some situations however, you may want to
exclude some files and archive members from the operation (for instance
if disk or storage space is tight). You can do this by excluding
certain files automatically (see section Choosing Files and Names for tar), or by performing
an operation interactively, using the --interactive (-w) option.
tar also accepts `--confirmation' for this option.
When the --interactive (-w) option is specified, before
reading, writing, or deleting files, tar first prints a message
for each such file, telling what operation it intends to take, then asks
for confirmation on the terminal. The actions which require
confirmation include adding a file to the archive, extracting a file
from the archive, deleting a file from the archive, and deleting a file
from disk. To confirm the action, you must type a line of input
beginning with `y'. If your input line begins with anything other
than `y', tar skips that file.
If tar is reading the archive from the standard input,
tar opens the file `/dev/tty' to support the interactive
communications.
Verbose output is normally sent to standard output, separate from
other error messages. However, if the archive is produced directly
on standard output, then verbose output is mixed with errors on
stderr. Producing the archive on standard output may be used
as a way to avoid using disk space, when the archive is soon to be
consumed by another process reading it, say. Some people felt the need
of producing an archive on stdout, still willing to segregate between
verbose output and error output. A possible approach would be using a
named pipe to receive the archive, and having the consumer process to
read from that named pipe. This has the advantage of letting standard
output free to receive verbose output, all separate from errors.
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