Tar and absolute pathnames

[bob desinger]

I received tar tapes with absolute pathnames enough times to write a
script to fix the problem, at least on System V.  The basic idea is to
do a chroot to the local directory (say, your $HOME) before reading the
tape.

Complications set in because you need to have the tar binary under the
new root; easy to fix by copying tar to the current directory.
Additionally, you need to make the node of the tape device from which
tar reads.  Only root can do the mknod on System V, so this script
wants you to be root.

The below script has System-V-isms in it (the pathname to tar is
hardwired, cringe; the /dev entry is specific to SysV; the chroot
command is in SysIII/V/Xenix but not BSD).  But at least it works.

Come to think of it, it runs `whoami', a BSD-ism that runs on several
System V implementations including HP-UX.  So it's not vanilla SysV.
Okay, for both of you who don't have `whoami' on your SysV box out
there, replace whoami with:

	id | sed -e 's/^[^(][^(]*(//' -e 's/).*$//'

bob desinger
bd%hpsemc at hplabs.HP.COM		{ucbvax, uunet}!hpda!hpsemc!bd

#! /bin/sh
# This is a shell archive.  Remove anything before this line,
# then unwrap it by saving it in a file and typing "sh file".
#
# Wrapped by bd at hpsemc on Thu Feb 11 17:17:36 1988
# Contents:
#	readtape 	

PATH=/bin:/usr/bin:/usr/ucb:/usr/local/bin:$PATH; export PATH
echo 'At the end, you should see the message "End of shell archive."'


echo Extracting readtape
cat >readtape <<'@//E*O*F readtape//'
#! /bin/sh
: Reads a tar tape written with absolute pathnames into a relative path.
# @(#)readtape	1.2	10/08/86
# Usage:
#	[1] % cd /some/directory/somewhere
#	[2] % cp `which readtape` readtape
#	[3] % su root -c "cd /some/directory/somewhere && ./readtape"

me=`basename $0`
USAGE="Usage (a three-step process):
	% cd /some/directory/somewhere
	% cp /usr/public/bin/readtape readtape
	% su root -c \"cd \`pwd\` && ./readtape\""

# We assume we're in the place where we want the files to land.
# We also assume that readtape is here already and that you're super-user now,
# but make sure of that first.

if [ ! -f ./readtape ]
then	echo >&2 "$me:  Sorry, no readtape in `pwd`"
	echo >&2 "$USAGE"
	exit 1
elif [ ! -x ./readtape ]
then	echo >&2 "$me:  Sorry, ./readtape isn't executable"
	echo >&2 "$USAGE"
	exit 1
elif [ `whoami` != root ]
then	echo >&2 "$me:  Sorry, you must be root to run readtape"
	echo >&2 "$USAGE"
	exit 1
elif [ $# -ne 0 ]
then	echo >&2 "$USAGE"
	exit 1
fi

# Here we know an executable readtape is here and that we're super-user.
# Get the tar program into a known place.

cp /usr/bin/tar tar

# Create the mag tape device file from which tar will read.

set - `ls -l /dev/rmt/0m`
# crw-rw-rw-   1 root     other      5 0x020000 Aug 22 14:30 /dev/rmt/0m
mkdir dev dev/rmt
mknod dev/rmt/0m c $5 $6
chmod 666 dev/rmt/0m

# Now read in the tape.

/etc/chroot `pwd` ./tar xp
tarstatus=$?

# Clean up after yourself.

dir=`pwd`
test $dir != /		&& rm -rf dev
test $dir != /usr/bin	&& rm -f  tar

# Exit, returning the status returned by tar.
exit $tarstatus
@//E*O*F readtape//

set `wc -lwc <readtape`
if test $1 -ne 61 -o $2 -ne 281 -o $3 -ne 1578
then	echo ! readtape should have 61 lines, 281 words, and 1578 characters
	echo ! but has $1 lines, $2 words, and $3 characters
fi
chmod 555 readtape

echo "End of shell archive."
exit 0