Avoid trapping by ssh ProxyCommand

Question

I have the following lines in my .ssh/config:

Host localhost
ProxyCommand none
Host n0*
ProxyCommand none

Host *
ProxyCommand corkscrew proxy.m.com 80 myserv 443 ~/.ssh/auth

i.e. for localhost and n0* ssh will not use the proxy, but for other hosts it will.

I got trapped several times know when I wanted to connect to other local machines, but couldn't connect because the proxy was active. There was no exception for them in ~/.ssh/config.

Is there away to echo an information to the command line, when the proxy is used? e.g.

$ ssh otherpc
  ---> using  ProxyCommand corkscrew proxy.m.com 80 myserv 443 ~/.ssh/auth
Password: 

I know that ssh -v is listing this line (along with many others):

debug1: Executing proxy command: exec corkscrew proxy.m.com 80 myserv 443 ~/.ssh/auth                                                                                                                                        

Is there less verbose way of displaying the proxy command used, helping me to avoid being trapped? Maybe a clever bash alias/function grepping ssh -v?

Warning: Don't write ssh() { ssh -v | grep Proxy}. I tried that too ... and accidently fork bombed me :P

Answer 1

I suggest that you write a small wrapper corkscrew-wrapper containing something like:

#!/bin/sh
echo "Executing proxy command corkscrew ..." > /dev/tty
exec corkscrew "$@"

and use corkscrew-wrapper instead of corkscrew in the ProxyCommand line.

If you want to support execution by at or cron, the following should work:

#!/bin/sh

cmd() { echo "Executing proxy command corkscrew ..."; }

{ cmd > /dev/tty; } 2> /dev/null
[ $? -eq 0 ] || cmd >&2

exec corkscrew "$@"

Note: do not detect the availability of /dev/tty with the tty command because the terminal is not necessarily connected to the standard input.