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Operating Systems Linux Ubuntu tar not reading if output directed to /dev/null Post 302351370 by bakunin on Tuesday 8th of September 2009 10:20:28 AM
Old 09-08-2009
tar not reading if output directed to /dev/null

I stumbled across a somewhat strange behavior of tar and find no explanation for it: i was testing a DVD for read errors and thought to simply tar the content and direct the output to /dev/null:

Code:
tar -cvf - /my/mountpoint/*ts > /dev/null

This way i expected the system to read the complete content and eventually to report a read error if there is one. To my amazement the command came back immediately without any error. Still i didn't believe it had read anything (save for maybe the directory information) so i directed the output to a real file instead.
Code:
tar -cvf - /my/mountpoint/*ts > /tmp/somefile

This time tar did read the files and subsequently reported the read error i was expecting in one file.

My question is, why didn't it read the files before? Is there something i am missing?

bakunin
 

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bup-join(1)						      General Commands Manual						       bup-join(1)

NAME
bup-join - concatenate files from a bup repository SYNOPSIS
bup join [-r host:path] [refs or hashes...] DESCRIPTION
bup join is roughly the opposite operation to bup-split(1). You can use it to retrieve the contents of a file from a local or remote bup repository. The supplied list of refs or hashes can be in any format accepted by git(1), including branch names, commit ids, tree ids, or blob ids. If no refs or hashes are given on the command line, bup join reads them from stdin instead. OPTIONS
-r, --remote=host:path Retrieves objects from the given remote repository instead of the local one. path may be blank, in which case the default remote repository is used. The connection to the remote server is made with SSH. If you'd like to specify which port, user or private key to use for the SSH connection, we recommend you use the ~/.ssh/config file. EXAMPLE
# split and then rejoin a file using its tree id TREE=$(tar -cvf - /etc | bup split -t) bup join $TREE | tar -tf - # make two backups, then get the second-most-recent. # mybackup~1 is git(1) notation for the second most # recent commit on the branch named mybackup. tar -cvf - /etc | bup split -n mybackup tar -cvf - /etc | bup split -n mybackup bup join mybackup~1 | tar -tf - SEE ALSO
bup-split(1), bup-save(1), ssh_config(5) BUP
Part of the bup(1) suite. AUTHORS
Avery Pennarun <apenwarr@gmail.com>. Bup unknown- bup-join(1)
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