What does the -f parameter do in the tar command

Question

When using tar I always include -f in the parameters but I have no idea why.

I looked up the man and it said;

-f, --file [HOSTNAME:]F

use archive file or device F (default
"-", meaning stdin/stdout)

But to be honest I have no idea what that means. Can anyone shed any light on it?

score 29 · Accepted Answer · edited Dec 15 '19 at 17:43

29

The -f option tells tar that the next argument is the file name of the archive, or standard output if it is -.

edited Dec 15 '19 at 17:43

Kusalananda

333,661

answered Aug 26 '10 at 10:19

ddeimeke

4,597

Ah, cheers! I presumed that the file name would have to appear next anyway so this -f was doing something more special! – Toby Aug 26 '10 at 10:45
7

@Toby: I suspect this is for historical reasons. "tar" is short for "tape archive", and presumably the original versions didn't envision people using disk files for archives all that often. – David Thornley Aug 27 '10 at 21:10

score 9 · Answer 2 · edited Dec 15 '19 at 17:31

9

Quite simple. If you omit the -f parameter, output is passed to stdout:

gammy@denice:/tmp/demo$ tar -c a b c
a0000644000175000017500000000000011435437117010223 0ustar  gammygammyb0000644000175000017500000000000011435437117010224 0ustar  gammygammyc0000644000175000017500000000000011435437117010225 0ustar  gammygammygammy@denice:/tmp/demo$ ls
a  b  c
gammy@denice:/tmp/demo$

...what a mess!

The -f-parameter (as you quoted) expects a filename (and optionally a hostname), hence the first argument after it is the output filename:

gammy@denice:/tmp/demo$ tar -cf output.tar a b c
gammy@denice:/tmp/demo$ ls
a  b  c  output.tar
gammy@denice:/tmp/demo$

edited Dec 15 '19 at 17:31

Mr Ethernet

105

answered Aug 26 '10 at 10:19

gamen

266

5

If you oppress the -f parameter, output is passed to stdout.

This is true with GNU tar, but I remember that on Solaris the default was a tape device (/dev/rmt0 or something like this).
– Cristian Ciupitu Aug 27 '10 at 18:42
*omit (not "oppress") – Mr Ethernet Dec 15 '19 at 15:19
1

Even GNU tar honours the no-longer-documented TAPE variable. For example, try TAPE=/tmp/tape.tar tar cv /etc/h* and then ls -l /tmp/tape.tar. – Chris Davies Dec 15 '19 at 17:35

score 2 · Answer 3 · answered Aug 26 '10 at 10:14

It lets you specify the file or device you're going to be working with. Either creating, updating or extracting things from it depending on other supplied flags. For example:

# Create a tar file with the contents of somepath/
tar -cvf filename.tar somepath/

# Extract the tar file.
tar -xvf filename.tar

What does the -f parameter do in the tar command

3 Answers3

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