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I am trying to pipe a tar/gzip archive into tar to decompress it. The script I have is part of a self extracting installer, where my archive is appended to the script. This works fine on linux, and the script looks like this:

export TMPDIR=`mktemp -d /tmp/selfextract.XXXXXX`

echo "TEMP: $TMPDIR"

ARCHIVE=`awk '/^__ARCHIVE_BELOW__/ {print NR + 1; exit 0; }' $0`


tail -n+$ARCHIVE $0 | tar xz -C $TMPDIR


exit 0

__ARCHIVE_BELOW__

The tar archive as a string is after the ARCHIVE_BELOW but I omitted it from here since it's huge.

However, when I do this on FreeBSD I get the following error:

tar: Failed to open '/dev/sa0'

I read that this is because free BSD expects to read from that device by default and you can tell it to read from stdin by passing -f - like so:

tail -n+$ARCHIVE $0 | tar zxf - -C $TMPDIR

However, when I do this I just get the error:

tar: Damaged tar archive
tar: Retrying...

Can anyone point out what I am doing wrong here? I need to do it this way (Via piping) for efficiency reasons.

Thanks

share|improve this question
    
Adding -v should at least tell you where it the process. You can also try to use -j instead of -z but it might be irrelevant with newer version. –  Alex Jun 10 at 17:57
    
Unfortunately that does not give me any more information or help resolve the issue. Thanks for the advice though. –  Casey Jordan Jun 10 at 18:42

1 Answer 1

In the first command:

echo $ARCHIVE | tar xz -C $TMPDIR

This is piping the file name into tar, not the contents of the file. How this is working is beyond me.

In the final command you list:

tail -n+$ARCHIVE $0 | tar zxf - -C $TMPDIR

I think this is specifying the file name as the argument to "tail", which probably isn't going to work either. Even if ${ARCHIVE} is a number, you still can't pipe the tail of an archive to tar, you need to give it the whole archive. Why are you calling tail here at all? A better solution might be:

tar xzvf ${ARCHIVE} -C ${TMPDIR}

share|improve this answer
    
Sorry, I tried to simplify this example and it seems I managed part of it. I have added a much fuller example above that should make this clearer. –  Casey Jordan Jun 13 at 1:26
    
I think the answer that getting the tail of an archive doesn't work still applies. –  Steve Wills Jun 16 at 0:05
    
Why does this work on linux then? –  Casey Jordan Jun 18 at 15:17

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