rsync won't exclude folders passed as a variable in a script

Question

I'm trying to pass a variable to exclude several folders from a rsync operation in a script, as follows:

echo "Type the path of the folders to exclude: "
while read folder
do
    folders=("${folders[@]}""$folder",)
while
rsync -avh source/* destination --exclude={"${folders[@]}"}

My source folder has the following structure:

- file1.txt
- file2.txt
- dir1
    - dir2
       - file3.txt
- dir2
    - flie4.txt
- dir3

When I run my script and type dir2, press , type dir3, press again and press + D to exit the while loop, rsync won't exclude the folders given, showing the result below:

$ ./script
Type the path to the folders to exclude:
dir2
dir3
sending incremental file list
created directory destination
file1.txt
file2.txt
dir1/
dir1/dir2/
dir1/dir2/file3.txt
dir2/
dir2/file4.txt
dir3/

if you run the script and echo the variable folders as echo "${folders[@]}" before calling rsync we get the value given dir2,dir3,, but I don't know why rsync isn't expanding the variable. I also tried to pass just $folders to the --exclude option, but although it still show the correct value, it won't get expanded inside the refered option.

The script will work only if I pass a value manually or pass the first value manually and just pass one folder inside the variable, as below:

folders="dir3"
rsync -avh source/ destination --exclude={dir2,"$folders"}

This makes me believe that everytime I put a comma inside the bash variable, rsync won't be able to recognize it as a comma or bash simply won't expand the variable.

Anyone knows what's happening? I don't have any clue.

I'm using ubuntu 20.04 Focal Fossa (Development Branch).

Answer 1

NB not properly tested; I added -n to the rsync command for testing purposes

Try something like:

#!/bin/bash

declare -a excludes

echo "Type the path of the folders to exclude: "
while IFS= read -r folder
do
    excludes+=( --exclude="$folder" )
done

rsync -n -avh "${excludes[@]}" -- source/ destination/