Tar

GNU Tar is everybody's favorite archive file format.

Use Cases

Get just one file

drush archive-backup (arb) and drush archive-restore (arr) are great commands for making a full site backup prior to changes; that you can use to restore from. Your entire Drupal instance (code, settings, modules, plus database) are all tar'd into an archive file, and gzip compressed . Again, one of the things that drush arb does is create a SQL dump file. What if you want just that dump file from the archive? The long way would be to extract the whole thing, find and move the bits you want, and then discard the rest. Or, you could just tell tar to give you the file you want explicitly:

# look at what's in the archive
tar -tf ~/drush-backups/archive-dump/20150327030955/freephile_drupal.20150327_030955.tar
# request just the SQL dump file (puts it into the current working directory)
tar -xf ~/drush-backups/archive-dump/20150327030955/freephile_drupal.20150327_030955.tar freephile_drupal.sql

Strip top level of the archive and don't extract a sub-folder

The magic tar one-line command to unpack a Drupal distribution over an existing Drupal directory (without clobbering your "sites" directory)

tar x --show-omitted-dirs --exclude sites --directory ../work/gr/iic-drupal/ \
--strip 1 -zf drupal-6.11.tar.gz

Drupal ships a tarball with the first object being a directory named after the release (e.g. drupal-6.11/)

This is a good thing, and the standard way of distributing a tar archive. If distributors didn't pack an archive using a top-level directory, then unsuspecting users could easily dump a whole bunch of files into an existing directory with no good way to clean up or undo their action.

But what do you do as a user when you really intend to dump the contents of the archive into an existing folder? You could extract the archive into a clean folder and then use copy to selectively move existing content back into the "clean" directory (e.g. cp -ar ./existingstuff/sites ./newstuff/sites ) In fact, that is the way described in the Drupal Handbook

But, if you want to do it all in one pass, you can use the combination of strip and directory options:

tar x --directory ~/existing-drupal --strip 1 -zf drupal-6.11.tar.gz

--strip 1 

removes the first path component of objects in the tar archive

--directory 

tells tar to change to a particular directory prior to extracting the contents of the archive

If you're upgrading a Drupal instance, then you already have a "sites" directory. You can skip over this directory in the tar archive with the exclude option. In fact, you can even have tar show you what you have skipped over with the show-omitted-dirs option. So, the best way that I know how to unpack a Drupal archive over an existing installation - all in one easy command - is

tar x --show-omitted-dirs --exclude sites --directory ../work/gr/iic-drupal/ --strip 1 -zf drupal-6.11.tar.gz

This didn't mess with my .git directory, .gitignore file and another top-level file I had called "crossdomain.xml"

Warning

Although I could not reproduce this behavior, I did once get my "sites" directory deleted. So, you do have backups and use version control right?

I restored it with

git checkout sites

and then I did a

git status

followed by

git commit -a -m 'adds changes in Drupal 6.11 security release'

Documentation

There is a lot more option information in the tar --help output than in the man page. Of course if you sudo apt-get install tar-doc then you can view the info manual. The "info" manual is also online at http://www.gnu.org/software/tar/manual/tar.html providing full documentation for tar.

Alternatives

star

S Tar (http://developer.berlios.de/projects/star and http://cdrecord.berlios.de/old/private/star.html) is an alternative Tape Archiver project that does not clobber newer items on disk by default It is available in Ubuntu, so sudo apt-get install star will install it for you.

Script that adds some interactive intelligence to tar

from http://www.cs.toronto.edu/~murray/code/hacks/untar

#!/bin/bash

# Wrapper script which tries to sensibly unpack the archive file(s) it's passed.
#
# The following archive formats are supported
#     .7z .a .ace .arj .cab .cpio .deb .lha .pmd .rar .rpm .tar{,.gz,.Z,.bz2}
#     .tnef .zip .zoo  and MIME/uuencoded mail attachments.
# (provided the necessary utilities are available).
#
# file(1) is used to diagnose the archive type so no file extension need be
# present. Also archives that are actually in one of the above formats but with
# a different extension, such as
#     .taz .tgz .jar .xpi
# will work.
#
# Features:
#     - Should unpack into a single subdirectory or file within the
#       current directory.
#     - If the archive would naturally dump into a single subdirectory it isn't
#       nested into a new one. (Although if you say no to clobbering the output
#       might be nested).
#     - World-writable bits are stripped off.
#     - When the archive would naturally unpack to an existing location you are
#       asked if you want to clobber it.
#
#       SAY "NO" WHEN ASKED TO CLOBBER UNLESS YOU KNOW *EXACTLY* WHAT WILL HAPPEN
#
#       When you say no the script will tell you the name of a randomly-named
#       directory in which you can find your archive contents.
#
#       Clobbering will trash files and possibly whole directories if the
#       archive contains files with the same name. Commonly named directories
#       should be merged. BUG: restrictive permissions on existing files and
#       directories can break this script.
#
# In Debian (or Ubuntu) packages exist for all of the utilities here. This is a
# complete list, although you probably don't need or want to install them all:
#    arj binutils bzip2 cabextract cpio dpkg gzip lha macutils mpack p7zip-full
#    ppmd procmail rpm sharutils tar tnef unace unrar unshield unzip zoo
#
# BUGS/Limitations:
#     - Robustness: your platform might not match my assumptions. It works for
#       me on Ubuntu GNU/Linux with the unarchiving utilities I have installed.
#     - You cannot unpack standard input, just files
#     - It's up to you to check the clobbering behaviour will be what you want.
#     - In an adversarial environment there could be some security issues.
#       In particular look around the mv and find operations for race conditions.
#       Basically I haven't invested the time necessary to make this safe
#       outside filesystems you control. This goes for many shell scripts.
#     - Permissions. As above the script may fail to clobber files depending on
#       permissions. Also the different archive utilities called by this script
#       do different things with permissions by default. I have not attempted to
#       make them consistent.
#
# I hope you can find a use for this script. But on the off-chance you had
# delusions to the contrary: there is ABSOLUTELY NO WARRANTY; USE AT YOUR OWN RISK.
#
# Iain Murray 2005, 2007

# After using my original script for a couple of years I finally fixed some
# issues in 2007:
#   - It's simpler to alter. Archive contents are no longer inspected before
#     unpacking; I just unpack somewhere and see what comes out. This makes
#     adding new file formats considerably easier and dealing with the utilities
#     more robust.
#   - The clobbering behaviour is now much better. Hopefully it should now be
#     consistent and most corner cases covered.
#   - World-writable permissions are not allowed. I discovered a large number of
#     world-writable files in my filespace due to unpacking from archives.
#     Mainly .zips I think as by default tar uses the user's umask rather than
#     the archive's bits. I could of course enforce a umask, but don't feel the
#     need at the moment.

set -e

ME=`basename $0`
TAR=tar

# This function takes a single file, works out what it is and unpacks it into
# the current directory
function unpack {
INFO=$(file "$1" | sed 's/[^:]*: //')
if echo $INFO | grep 'gzip compressed' > /dev/null ; then
"$TAR" zxf "$1"
elif echo $INFO | grep "compress'd" > /dev/null ; then
uncompress -c "$1" | "$TAR" x
elif echo $INFO | grep "bzip2 compressed" > /dev/null ; then
bzcat "$1" | "$TAR" x
elif echo $INFO | grep -i "tar archive" > /dev/null ; then
"$TAR" xf "$1"
elif echo $INFO | grep "Zip archive" > /dev/null ; then
unzip "$1"
elif echo $INFO | grep "RAR archive" > /dev/null ; then
unrar x -ap. "$1"
elif echo $INFO | grep "7-zip" > /dev/null ; then
7z x "$1"
elif echo $INFO | grep "RPM " > /dev/null ; then
rpm2cpio "$1" | cpio -i --no-absolute-filenames -d --quiet
elif echo $INFO | grep "cpio archive" > /dev/null ; then
cpio -i --no-absolute-filenames -d --quiet < "$1"
elif echo $INFO | grep "Debian .* package" > /dev/null ; then
dpkg-deb -x "$1" .
elif echo $INFO | grep -i " ar archive" > /dev/null ; then
ar x "$1"
elif echo $INFO | grep -i "ACE archive" > /dev/null ; then
unace e "$1"
elif echo $INFO | grep -i "ARJ archive" > /dev/null ; then
arj e "$1"
elif echo $INFO | grep -i "ZOO archive" > /dev/null ; then
zoo x "$1"
elif echo $INFO | grep -i "\(tnef\|Transport Neutral Encapsulation Format\)" > /dev/null ; then
tnef "$1"
elif echo $INFO | grep -i "InstallShield CAB" > /dev/null ; then
unshield x "$1"
elif echo $INFO | grep -i "LHa" > /dev/null ; then
lha x "$1"
elif echo $INFO | grep -i "\(mail\|news\)" > /dev/null ; then
formail -s munpack < "$1"
elif echo $INFO | grep -i "uuencode" > /dev/null ; then
uudecode "$1"
elif echo $INFO | grep -i "cab" > /dev/null ; then
cabextract "$1"
elif echo $INFO | grep -i "PPMD archive" > /dev/null ; then
# Insists on file being in same directory.
ln -s "$1" .
ppmd d "$1"
rm `basename "$1"`
else
echo $ME: Sorry I do not know about files of type \"$INFO\"
fi
}

# Some systems come with a fullname command, but providing one here won't hurt:
function fullname {
if [ "${1:0:1}" = '/' ] ; then    # ${::} is a bashism, don't use /bin/sh
echo "$1"
else
echo "$PWD/$1"
fi
}

function mergedirs {
# Copy contents of directory $1 into directory $2
# Delete anything that exists in $1 from $2
# WARNING: this is tricky
#
TARGET=`fullname "$2"`
ORIG_PWD="$PWD"
cd "$1"
# Remove files and directories in the way of files
find . \! -type d -exec rm -Rf "$TARGET"/'{}' \;
# Remove files in the way of directories. Don't remove directories (no -R
# option to rm) or contents not in the archive will be lost.
find . -type d \! -name '.' -exec rm -f "$TARGET"/'{}' \; 2> /dev/null
# Move directories (will only succeed when directories don't exist)
# After this whole directory structure should exist.
find . -type d \! -name '.' -exec mv -T '{}' "$TARGET"/'{}' \; 2> /dev/null
# Move any remaining files (in top level and those within unmoved directories)
find . \! -type d -exec mv '{}' "$TARGET"/'{}' \; 2> /dev/null
# Delete anything that hasn't moved (hopefully just empty directories, but
# I'm being a bit cavalier here) so that rmdir will work
find . -maxdepth 1 \! -name '.' -exec rm -Rf '{}' \;
cd "$ORIG_PWD"
rmdir "$1"
return 0
}

function agree_to_clobber {
read -p "Clobber y/n [n]? " response
echo $response | grep '^[Yy]' > /dev/null
return
}

function mvqueryclobber {
# Arguments: 1=source_archive_file 2=unarchived_output 3=target_location
# Attempt to move $2 to $3, but ask before breaking anything and just
# return 1 if doing the move seems dangerous or confusing.
if [ -e "$3" ] ; then
if [ -f "$2" -a -f "$3" ] ; then
# Source and target are both ordinary files
echo $ME: Would you like to clobber existing file
echo     "$3"
echo with the file just unpacked from `basename $1` ?
if agree_to_clobber ; then
mv -f "$2" "$3"
return
fi
fi
if [ -d "$3" -a -d "$2" ] ; then
# Source and target are both directories
echo $ME: Would you like to clobber existing data in
echo     "$3"
echo with the data just unpacked from `basename $1` ?
echo 'WARNING: this can be really bad idea (only say yes if very sure)'
if agree_to_clobber ; then
mergedirs "$2" "$3"
return
else
return 1
fi
else
# Source and target are mix of file-types, or are weird files. Don't
# want risk the move as bad things might happen.
return 1
fi
else
# Target doesn't currently exist so try simple move
if mv "$2" "$3" ; then
return 0
else
return 1
fi
fi
}

for input_file in "$@" ; do
if [ \! -e "$input_file" ] ; then
echo "$ME: $input_file does not exist."
exit 1
fi
input_file_fullname=`fullname "$input_file"`

# Safely extract into randomly-named out_dir, not allowing any
# world-writable bits that may be set by archive program
out_dir=`echo "$input_file"_$RANDOM | sed -e 's/.*\///'`
mkdir "$out_dir"
user_perms=`stat --format="%a" "$out_dir"`
chmod o-rwx "$out_dir"
cd "$out_dir"
unpack "$input_file_fullname"
chmod -R o-w .
chmod "$user_perms" .

# Once extracted need to move into nicely named place. But this risks
# clobbering and depends on how many files came out of the archive. This
# (hopefully) deals with all the corner cases:
output_files=(*)
num_files=${#output_files[*]}
cd ..
if [ "$output_files" = "*" ] ; then
echo $ME: Extracted no files from $input_file
rmdir "$out_dir"
elif [ $num_files -eq 1 ] ; then
if mvqueryclobber "$input_file" "$out_dir/$output_files" "$output_files" ; then
echo $ME: Extracted $input_file to $output_files
rmdir "$out_dir"
else
echo $ME: Extracted $input_file to $out_dir/$output_files
fi
else
# Expanded into multiple files, need to make up a nice directory name to put them in
# by knocking off something that looks like a file extension or adding
# _contents to the archive name.
nicer_out_dir=`echo "$input_file"_contents | sed -e 's/.*\///' \
-e 's/\(.\)\(\.tar\|\)\.[a-z0-9]\{1,4\}_contents$/\1/i'`
if mvqueryclobber "$input_file" "$out_dir" "$nicer_out_dir" ; then
echo $ME: Extracted $input_file to $nicer_out_dir
else
echo $ME: Extracted $input_file to $out_dir
fi
fi
done

See Also

Sometimes you end up with a directory nested in it's intended destination (like drush arb can leave you with /var/www/drupal/drupal). See the Bash article for moving a nested directory up a level.

Gnu's Not Unix, because Unix is proprietary software while Gnu is software that respects your freedom.