rsync
Rsync between hosts, using a jump host’s ssh keys as the intermediary:
cat raw.old.new.list | awk '{ print( " ssh " $1 " \x27 " "rsync -avP /app/users " $2 ":/app \x27 ") }'
# and to run it...
cat raw.old.new.list | awk '{ system( " ssh -A " $1 " \x27 " "rsync -avP /app/users " $2 ":/app \x27 ") }'