Reject anything but rsync through ssh

force_rsync.sh

#!/bin/sh

# Script to reject anything but rsync through ssh.
# Source: https://troy.jdmz.net/rsync/index.html
#
# To force run it on new ssh connections, add:
# command="/home/USER/force_rsync.sh"
# to /home/USER/.ssh/authorized_keys, at the start
# of the key line of enforced user.

case "$SSH_ORIGINAL_COMMAND" in
*\&*)
    echo "Rejected"
;;
*\(*)
    echo "Rejected"
;;
*\{*)
    echo "Rejected"
;;
*\;*)
    echo "Rejected"
;;
*\<*)
    echo "Rejected"
;;
*\>*)
    echo "Rejected"
;;
*\`*)
    echo "Rejected"
;;
*\|*)
    echo "Rejected"
;;
rsync\ --server*)
    $SSH_ORIGINAL_COMMAND
;;
*)
    echo "Rejected"
;;
esac