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Conditional Bug?

Howdy zshers,

I'm using I have the following script to backup my important files, and I've
been running it from cron and getting errors from the tar command.
I'm concerned about the conditional at line 22: is my usage wrong or
is this a bug?  The conditional says that the file exists (when it
does not) and therefore runs the "--update" version of tar.

Traced invocation from shell prompt ("joel@W0053328:~% " is my prompt):
joel@W0053328:~% zsh --version

zsh 4.3.2 (i486-slackware-linux-gnu)

joel@W0053328:~% /home/joel/bin/backup -t /mnt/backup/backup.tar.bz2 ~/ado ~/data ~/docs ~/svn_repo ~/Mail ~/News ~/lisp ~/office-directory ~/.emacs ~/.emacs-custom.el

+/home/joel/bin/backup:37> FILE='' 
+/home/joel/bin/backup:38> getopts t: opt
+/home/joel/bin/backup:40> case t (t)
+/home/joel/bin/backup:41> export 'FILE=/mnt/backup/backup.tar.bz2'
+/home/joel/bin/backup:38> getopts t: opt
+/home/joel/bin/backup:47> shift 2
+/home/joel/bin/backup:48> export 'TOBACKUP=/home/joel/ado /home/joel/data /home/joel/docs /home/joel/svn_repo /home/joel/Mail /home/joel/News /home/joel/lisp /home/joel/office-directory /home/joel/.emacs /home/joel/.emacs-custom.el'
+/home/joel/bin/backup:51> [[+/home/joel/bin/backup:1> grep -e backup /etc/mtab
+/home/joel/bin/backup:51> [[ -z '' ]]
+/home/joel/bin/backup:52> mount /dev/backup
+/home/joel/bin/backup:55> backup /mnt/backup/backup.tar.bz2 '/home/joel/ado /home/joel/data /home/joel/docs /home/joel/svn_repo /home/joel/Mail /home/joel/News /home/joel/lisp /home/joel/office-directory /home/joel/.emacs /home/joel/.emacs-custom.el'
+backup:2> export 'FILE=/mnt/backup/backup.tar.bz2'
+backup:3> shift
+backup:4> export 'TOBACKUP=/home/joel/ado /home/joel/data /home/joel/docs /home/joel/svn_repo /home/joel/Mail /home/joel/News /home/joel/lisp /home/joel/office-directory /home/joel/.emacs /home/joel/.emacs-custom.el'
+backup:7> [[ -e /mnt/backup/backup.tar.bz2 ]]
+backup:9> bunzip2 /mnt/backup/backup.tar.bz2
+backup:11> tar --update -f /mnt/backup/backup.tar '/home/joel/ado /home/joel/data /home/joel/docs /home/joel/svn_repo /home/joel/Mail /home/joel/News /home/joel/lisp /home/joel/office-directory /home/joel/.emacs /home/joel/.emacs-custom.el'
tar: Removing leading `/' from member names
tar: /home/joel/ado /home/joel/data /home/joel/docs /home/joel/svn_repo /home/joel/Mail /home/joel/News /home/joel/lisp /home/joel/office-directory /home/joel/.emacs /home/joel/.emacs-custom.el: Cannot stat: No such file or directory
tar: Error exit delayed from previous errors
+backup:17> bzip2 -9 /mnt/backup/backup.tar
+/home/joel/bin/backup:56> umount /dev/backup
+/home/joel/bin/backup:57> exit 0
Here's the script:

#! /bin/zsh -x
# shell script to back up important documents
# should put in cron for 02:00 every night
# 16/10/2007 - h.11:39

# example syntax:
# backup -t /mnt/backup/backup_jja.tbz2 ~/docs ~/data ~/ado ~/bin ~/lisp \
#   ~/svn-repo
# pseudocode  in comments

# for now, backup device is /dev/backup; this could be a link to
# another device if  the user so desires

# backup function (archive file, directories to back up)
backup() {
# 0. parse arguments: first arg is filename, rest are directories to back up
    export FILE=$1;
    export TOBACKUP="$*";
# 1. unzip the archive file in its current location (bunzip2)
    # test to see if the file exists
    if [[ -e $FILE ]]; then
    # yes -- unzip it
    	bunzip2 $FILE
    # 2 . update the archive with the listed files
	tar --update -f ${FILE/.bz2} $TOBACKUP
    # no
	tar -cvf ${FILE/.bz2} $TOBACKUP
# 3.  bzip2 it back up
    bzip2 -9 ${FILE/.bz2}
# done

# parse commands
while getopts t: opt
    case $opt in
    t) export FILE=$OPTARG;;
    '?') echo "$0: Please supply the name of a backup file" >&2
	    exit 1;;

shift $((OPTIND - 1))
export TOBACKUP="$*"

# is the backup disk mounted?
if [[ -z `grep -e "backup" /etc/mtab` ]]; then # not mounted
    mount /dev/backup 

backup $FILE $TOBACKUP || exit 1
umount /dev/backup
exit $?				


Joel J. Adamson
Pediatric Psychopharmacology Research Unit
Massachusetts General Hospital
Boston, MA  02114
(617) 643-1432
(303) 880-3109

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