Expanding variables in zsh

Question

The script below works in bash but not in zsh. I think it is because in the variable OPTS, I am "expanding" (not sure if this is the right word) the variable $EXCLUDE, and this syntax doesn't work in zsh. How would I replace that line to make it work on zsh?

SRC="/path_to_source"
DST="/path_to_dest"
EXCLUDE=".hg"  
OPTS="-avr --delete --progress --exclude=${EXCLUDE} --delete-excluded"                                               

rsync $OPTS $SRC $DST   

Answer 1

The problem here is that $OPTS is not split into several arguments on the rsync command line. In zsh syntax, use:

rsync ${=OPTS} $SRC $DST 

(an alternative is to simulate standard shell behavior globably with the option -o shwordsplit…)

From the manpage:

One commonly encountered difference [in zsh] is that variables substituted onto the command line are not split into words. See the description of the shell option SH_WORD_SPLIT in the section 'Parameter Expansion' in zshexpn(1). In zsh, you can either explicitly request the splitting (e.g. ${=foo}) or use an array when you want a variable to expand to more than one word. See the section 'Array Parameters' in zshparam(1).

Answer 2

The problem doesn't come from $EXCLUDE, it comes from $OPTS. Your script relies on word splitting happening to $OPTS. This is a bad idea; for example it will fail if you ever change $EXCLUDE to contain a pattern and --exclude=$EXCLUDE comes to match a file in the current directory, or if you ever change $EXCLUDE to contain whitespace.

$OPTS is a list of words, not a word. If you only need your script to work in ksh, bash and zsh, make it an array:

SRC="/path_to_source"
DST="/path_to_dest"
EXCLUDE=".hg"
OPTS=(-avr --delete --progress --exclude="$EXCLUDE" --delete-excluded)
rsync "${OPTS[@]}" "$SRC" "$DST"

If you only intend the script to work in zsh, you can simplify the last line:

rsync $OPTS $SRC $DST

If you want the script to work in every shell, you need to use the positional parameters. They are the only array available.

set -- -avr --delete --progress --exclude="$EXCLUDE" --delete-excluded
rsync "$@" "$SRC" "$DST"

If you have a shell script that you want to be able to run conveniently with zsh, put this line at the beginning — it tells zsh to act like ksh, and it's a no-op on other shells.

emulate ksh >/dev/null 2>/dev/null

Answer 3

To complete Stéphane Gimenez answer (I cannot comment yet), one solution is to make your script portable to bash by checking if you are using zsh and then transform $OPTS into an array like this

[ -n "${ZSH_VERSION:-}" ] && set -A OPTS ${=OPTS}

Then your rsync command will work.