Rupert Heesom on Fri, 20 Apr 2001 00:00:19 -0400

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Re: [PLUG] TAR command line question

On 19 Apr 2001 13:30:43 -0400, Jeff Abrahamson wrote:
> On Thu, Apr 19, 2001 at 10:50:41AM -0400, Rupert Heesom wrote:
> > In my LPIC studies, the command line of "TAR CVFB /DEV/TAPE 20 /" is
> > supposed to be correct because the order of the modifiers are the same
> > as the arguments.
> > 
> > Now, when I look at the command line,  assuming that the modifier "C"
> > correlates to "/dev/tape", "F" to "/" and "B" to "20", I think that the
> > arguments should be in the order of "/dev/tape / 20".
> > 
> > Am I wrong?
> On several counts, I'm afraid.
> First, unix is case sensitive, so I presume you mean
>        tar cvfb /dev/tape 20 /

Yes, sorry for that oversight; I wanted the syntax to be clear in the
msg (CAPS are easier to read), not realising that it was actually
incorrect in the end.

> Now, assuming that's what you mean, you can see in tar(1) that
>      c              means create a new archive
>      v              means verbose (echo names as they are added to archive)
>      f              file name of archive, so /dev/tape
>      b              blocking factor, so 20
> and then any further arguments are the files to archive, in this case
> /.
> As long as you are using gnu tar, it will warn you that it is
> stripping the leading / from the name. To be safe and proper, though,
> you should cd to / and archive .
>     (cd / && tar cvfb /dev/tape 20 /)

I'm beginning to see this, it's still a bit confusing though!

If we take command line ---  tar c v  f  b    /dev/tape   20   /
(spaced out for clarity)
and we pair off the                           1  2         1           2
modifiers with args -

So, tar's "c" and "v" switches have no args, and the "/" arg has no
switch or modifier.
The only switches that need args are the "f" and "b" switches.

Am I starting to understand this??

> This way if you want to restore some day, you can choose where to
> restore to. This is important.
> You can also use long option names, allowing you to say
>     tar --create --verbose --file=/dev/tape --blocking-factor=20
> which might be clearer in a script.

That part is very interesting, I kinda like that approach, very visibly
"unconfusing", except you left out the source to archive (an ending
"/"?)  !!

Thanks for your time to reply!


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