Howto inflate AND extract a .tar.bz2 using the 7-zip command line tool

7ztar

I have a .tar.bz2 file that I want to be decompressed and extracted via the 7-zip commandline tool.

So basically I'm looking for the equivalent of

tar -xjf foo.tar.bz2

with 7-zip there is only the option "x" for extract, so doing

7z x foo.tar.bz2

gives me the inflated foo.tar file instead of unpacking all the directories inside the tar.
What's the corresponding option for 7z?

Best Answer

With 7zip, you have to run the command twice, once to decompress and again to extract. The tar file format is just a "wad" of everything stuck end to end. Then the whole tar file is compressed using various compression algorithms, in your example bzip. Basically the resulting file has two layers. When you "extract" the bzip layer you get a tar file, then when you extract the tar file you get a bunch of individual files.

7zip doesn't handle multiple layers at once, although it is able to handle both layers:

7z x foo.tar.bz2
7z x foo.tar

Actually the standard unix tools work the same way:

bunzip2 foo.tar.bz2
tar xf foo.tar

However the the unix tar command has convenience features that call the secondary compression and decompression steps using another program before/after it handles the tar part. Basically the -j argument calls bzip2/bunzip2, you just don't see the second step. Likewise -z will call gzip/gunzip, etc.

Related Solutions

Find – Recursively Search All Archive Files for Filename Patterns

(Adapted from How do I recursively grep through compressed archives?)

Install AVFS, a filesystem that provides transparent access inside archives. First run this command once to set up a view of your machine's filesystem in which you can access archives as if they were directories:

mountavfs

After this, if /path/to/archive.zip is a recognized archive, then ~/.avfs/path/to/archive.zip# is a directory that appears to contain the contents of the archive.

find ~/.avfs"$PWD" \( -name '*.7z' -o -name '*.zip' -o -name '*.tar.gz' -o -name '*.tgz' \) \
     -exec sh -c '
                  find "$0#" -name "*vacation*.jpg"
                 ' {} 'Test::Version' \;

Explanations:

Mount the AVFS filesystem.
Look for archive files in ~/.avfs$PWD, which is the AVFS view of the current directory.
For each archive, execute the specified shell snippet (with $0 = archive name and $1 = pattern to search).
$0# is the directory view of the archive $0.
{\} rather than {} is needed in case the outer find substitutes {} inside -exec ; arguments (some do it, some don't).

Or in zsh ≥4.3:

mountavfs
ls -l ~/.avfs$PWD/**/*.(7z|tgz|tar.gz|zip)(e\''
     reply=($REPLY\#/**/*vacation*.jpg(.N))
'\')

Explanations:

~/.avfs$PWD/**/*.(7z|tgz|tar.gz|zip) matches archives in the AVFS view of the current directory and its subdirectories.
PATTERN(e\''CODE'\') applies CODE to each match of PATTERN. The name of the matched file is in $REPLY. Setting the reply array turns the match into a list of names.
$REPLY\# is the directory view of the archive.
$REPLY\#/**/*vacation*.jpg matches *vacation*.jpg files in the archive.
The N glob qualifier makes the pattern expand to an empty list if there is no match.

Tar – Transform a Tar Archive’s Paths Without Extracting It

You could mount the archive with archivemount or mountavfs and recreate it again

archivemount tarfile.tar /mnt
cd /mnt
tar cf /tmp/tarfile.tar --transform 's/foo/bar/' .

write operations on the archive filesystem will perfom a full rewrite on umount, so don't seem a good option for large files.

EDIT

I don't know implementation details but seem like we are saving the write files to filesystem step.

Just test to solve dudes, (over a tar of my /usr)

#!/bin/bash

# try to avoid slab cache issues 
cat /tmp/usr.tar > /dev/null

T="$(date +%s)"
tar xf /tmp/usr.tar
tar cf usr.tar usr --transform 's/usr/foo/'
T="$(($(date +%s)-T))"
echo "Tar/Untar seconds: ${T}"

T="$(date +%s)"
archivemount -o readonly -o nobackup /tmp/usr.tar /mnt
tar cf usr.tar /mnt  --transform 's/usr/foo/'
umount /mnt
T="$(($(date +%s)-T))"
echo "Archivemount seconds: ${T}"

T="$(date +%s)"
mountavfs
cd '/root/.avfs/tmp/usr.tar#'
tar cf /tmp/test/usr.tar   --transform 's/usr/foo/' .
T="$(($(date +%s)-T))"
echo "Avfs seconds: ${T}"

Output:

Tar/Untar seconds: 480
Archivemount seconds:  failure, a lot of read errors.
Avfs seconds: 217

So Avfs wins!.

Best Answer

Related Solutions

Find – Recursively Search All Archive Files for Filename Patterns

Tar – Transform a Tar Archive’s Paths Without Extracting It

Related Question