Heck, for a string manipulation that simple you don't even need `sed`, you can just use the shell -- modulo potential escaping errors (I haven't actually tested

Heck, for a string manipulation that simple you don't even need `sed`, you can just use the shell -- modulo potential escaping errors (I haven't actually tested this), something like this should do the trick: ProxyCommand ssh -aY bastion 'nc -w 900 `x="%h"; echo ${x%%.bast}` %p'