I log into a lot of servers via ssh. Typically I just use the easy bash history search to scroll through my history of 'ssh' commands and find the one I want. However, eventually my .bash_history reaches its limit and I start losing entries, despite increasing the limits, etc.. 
I would rather just adjust my $PROMPT_COMMAND so that after every command, it checks to see if I ran a command with ssh, and if so, appends that command to a file somewhere. 
I saw some relevant questions asked here and here but I am struggling to understand how to use these in a function that I can source from my .bashrc and add to my $PROMPT_COMMAND that will check if the last command entered started with ssh and copy it to a file.
For example, this does not work:
$ PROMPT_COMMAND="echo; foo; "
$ foo () { echo "command was: $BASH_COMMAND" ; }
$ ssh cn-0030
...(Ctrl-D)...
$ logout
Connection to cn-0030 closed.
command was: echo "command was: $BASH_COMMAND"
This also does not work:
$ foo () { echo !! | grep ssh --color ; }
Because !! gets expanded into the actual last command run immediately and then saved into foo, instead of being evaluated when foo is evaluated
