Using rsync to transfer a file from/to a server using two hop SSH

gistfile1.sh

# Command used to send a file to a remote server B only reachable through a remote server A
# Local <----> A <----> B

# receive
rsync -av --append -e 'ssh -o "ProxyCommand ssh user@server_A exec nc %h %p 2>/dev/null"' user@server_B:/path/source.file destination.file
# send
rsync -av --append -e 'ssh -o "ProxyCommand ssh user@server_A exec nc %h %p 2>/dev/null"' destination.file user@server_B:/path/source.file