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Date:      Fri, 31 May 2002 22:13:21 -0500
From:      Dan Nelson <dnelson@allantgroup.com>
To:        Peter Leftwich <Hostmaster@Video2Video.Com>
Cc:        Matthias Buelow <mkb@mukappabeta.de>, FreeBSD LIST <FreeBSD-Questions@FreeBSD.Org>
Subject:   Re: mv vs. tar [overlapping,same fs]
Message-ID:  <20020601031320.GC91922@dan.emsphone.com>
In-Reply-To: <20020531224423.V64670-100000@earl-grey.cloud9.net>
References:  <20020530024553.GC78068@dan.emsphone.com> <20020531224423.V64670-100000@earl-grey.cloud9.net>

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In the last episode (May 31), Peter Leftwich said:
> On Wed, 29 May 2002, Dan Nelson wrote:
> > Even to different filesystems.  A single process can only be reading or writing, and when it's blocked reading, it can't be writing.  If you are copying files over a couple meg, it also helps to increase the buffering between the two tars by putting team (from ports) inbetween them, and raising tar's blocksize:
> > ( cd /source ; tar cbf 128 - . ) | team 1m 4 | ( cd /destination ; tar xbpf 128 - )
> 
> Very interesting.  I hardly ever use Unix's/FreeBSD's/tcsh's "-"
> command line but your example makes me want to learn how to master it
> :) Now does your usage work "as is" ... ie. what is with the
> parentheses?  If set between "back apostrophes" such as ` ` these,
> would that command line work?

"-" is a per-command feature.  Some allow you to process stdin/stdout
that way, some don't.

The parens create subshells, so that the cd commands don't affect the
shell you're typing in.  Using backtics creates a subshell too, but
would then try and execute the output of the command.  In this
particular example, it should do nothing, since tar doesn't normally
print anything to stdout.

cd /usr ; ( cd /tmp ; touch file1 ) ; touch file2

creates /tmp/file1 and /usr/file2.  Take a look at the sh manpage.
 
> Do different *mounted partitions* on one HD count as "/same/"
> filesystem?

Nope.  Different filesystems.

-- 
	Dan Nelson
	dnelson@allantgroup.com

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