I'm trying to determine the size of the files that would be newly copied when syncing two folders by running rsync in dry mode and then summing up the sizes of the files listed in the output of rsync.

Currently I'm stuck at prefixing the files by their parent folder. I found out how to prefix lines using sed and how to escape using sed, but I'm having troubles combining those two.

This is how far I got:

source="/my/source/folder/"
target="/my/target/folder/"
escaped=`echo "$source" | sed -e 's/[\/&]/\\//g'`
du `rsync -ahnv $source $target | tail -n +2 | head -n -3 | sed "s/^/$escaped/"` | awk '{i+=$1} END {print i}'

This is the output I get from bash -x myscript.sh

+ source=/my/source/folder/
+ target=/my/target/folder
++ echo /my/source/folder/
++ sed -e 's/[\/&]/\//g'
+ escaped=/my/source/folder/
+ awk '{i+=$1} END {print i}'
++ rsync -ahnv /my/source/folder/ /my/target/folder/
++ sed 's/^//my/source/folder//'
++ head -n -3
++ tail -n +2
sed: -e expression #1, char 8: unknown option to `s'
+ du
80268

Any ideas on how to properly escape would be highly appreciated.