tar not reading if output directed to /dev/null Post: 302351370

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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

09-08-2009

Registered User

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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shape_tar

SHAPE_TAR(1)						      General Commands Manual						      SHAPE_TAR(1)

NAME

       shape_tar - shapeTools RMS bundle up subsystem in a tar or shar archive

SYNOPSIS

	shape tar[VERSIONS=<version_selection_rule>] [ARCHIVE=<filename>]

       shape shar[VERSIONS=<version_selection_rule>] [ARCHIVE=<filename>]

DESCRIPTION

       Shape tar and shape shar create a tar or a shar archive containing all source components of the current node in the system tree. All source
       components listed in the COMPONENTS macro in the Makefile and the release identification file (VERSIONFILE) are	written  to  the  archive.
       Components of subsystems are not included in the archive file.

       The  VERSIONS  macro  may  be  set  to  specify a version selection rule to be active during archive file creation. Default is most_recent,
       selecting the most recent version of each component. See shape_stdrul(7) or the $(SHAPELIBPATH)/stdrules for other possible  settings.  You
       may also use self defined version selection rules as VERSIONS.

       ARCHIVE	is  the base name of the file where the output shall be written to. Default is $(SUBSYSTEMNAME). The output file gets the filename
       extension .tar (resp. .shar).  When ARCHIVE=- is given, data will be written to standard output.

SEE ALSO

       shape_RMS(1), shape_stdrul(7)

FILES

       $(SUBSYSTEMNAME).tar $(SUBSYSTEMNAME).shar

20.7.119															      SHAPE_TAR(1)

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