Error in docker-entrypoint.sh

[SwedishGojira]

I noticed that whatever I did my 1.9.0 docker container running in Unraid stopped syncing because it was stuck on an old Dropbox version and would not update Dropbox so I tried running the commands for updating Dropbox line by line from docker-entrypoint.sh and got stuck with a "Bad substitution"-errormessage when I ran the command to strip the linebreaks and newlines from the download url of the latest Dropbox version.
# Strip CRLF DL=${DL//[$'\t\r\n ']}

I cleaned the URL manually and everything worked out after that and I am now running a fresh version 144.4.4491 of Dropbox and everything is syncing.

I am just an amateur scripter and could not solve it, but I'm sure you could figure it out.