Shell Programming and Scripting

Hello.

I am writing a backup script which uses a function to create a tar archive for a specified directory. For some reason though I cannot get tar to exclude a specified path when passed as a variable. The problem does not seem to be with the command though as it works when entered in the script directly.

Here are the relevant portions of the script:

Code:

BUP_ROOT=$HOME/backup
bup_files () {
   cd $2
   [[ "$3" ]] && BUP_EXCLUDE="--exclude='$3'" || BUP_EXCLUDE=""
   tar $BUP_EXCLUDE -czf $BUP_ROOT/$1.tgz ./
}

bup_files name_of_archive /path/to/archive "download/*"

This works except the specified directory is not excluded. If I put an 'echo' in front of the tar command it shows the $BUP_EXCLUDE variable is being set and with what I would expect. e.g.

Code:

tar --exclude='download/*' -czf /home/username/backup/name_of_archive.tgz ./

Wondering if the use of putting the whole exclusion option in a variable was a problem, as a test I rewrote the command as

Code:

tar --exclude='$3' -czf $BUP_ROOT/$1.tgz ./

This did not make any different though. As a final test I put the exclusion directly in the tar command

Code:

tar --exclude='download/*' -czf $BUP_ROOT/$1.tgz ./

This worked, the archive was created with the required path excluded. This leads me to think there is some problem with the shell passing the variable correctly rather than with the tar command. The wildcard is supposed to be a literal for tar to do its own pattern matching, and by testing with echo in front of the tar command it does seem to be passed as one, there is no globbing. I have even tried putting quotes around the $BUP_EXCLUDE" variable in the tar command to see if that helps with no effect.

The shell is BASH version 3.00.15 and I have tried searching for a solution with no luck so I hope I am missing something obvious here.

Thanks,

Michael.

'$3' does not allow the shell to expand the variable use double quotes

Would the single quotes still have that effect inside double quotes?

It fixed the problem though, in hindsight I was being totally dumb using them to prevent globbing when this never would have happened anyway being inside the double quotes.

So I am wondering whether rather than preventing the variable being expanded, the single quotes were just being passed to tar as part of the exclude pattern, and so it was failing for that reason?

Either way, it has fixed the problem.

Many thanks,

Michael.