How can I run complicated commands on establishing a mosh connection? - shell

Question

With ssh I can do this:
ssh REMOTE -t 'tmux a || tmux'
With mosh the best I can do is this:
mosh REMOTE -- tmux a
But this won't work:
mosh REMOTE -- tmux a || tmux
Neither does this: (It doesn't matter whether it's single quote or double quote, I tried both)
mosh REMOTE -- 'tmux a || tmux'
So, my question is: How am I supposed to do this job?

Answer 1

Well, it seems that I have to explicitly use a shell to execute command:
mosh REMOTE -- sh -c 'tmux a || tmux'
EDIT
Instead of doing tmux a || tmux, a better way is add new-session to ~/.tmux.conf and just run tmux. That would make things much easier. I can do things like this now:
mosh REMOTE -- tmux
Awesome!

Answer 2

There might be more complicated commands than the examples given above. I wanted to make a command that reattaches to an existing tmux session if one exists but is not already attached, or a new one if there are none available.
Looking at this example, I would have done something like this:
function tmosh() {
mosh $1 -- (tmux ls | grep -vq attached && tmux at -t $( tmux ls | grep -vm1 attached | cut -d: -f1 ) ) || tmux new
}
But that doesn't work, per the original question above.
My solution so far is to have a wrapper script on the host servers:
tmux-reattach-if-exists
which consists simply of:
(tmux ls | grep -vq attached && tmux at -t $( tmux ls | grep -vm1 attached | cut -d: -f1 )) || tmux new
Then I used called the script on the client from mosh like this:
function tmosh() {
mosh $1 -- tmux-reattach-if-exists
}
If there's a solution that can do this via .tmux.conf directly that would be great but I couldn't seem to work that out.

Answer 3

Put this at the end of your .bashrc
s1="`ps $PPID|grep mosh|awk '{print $5}'`"
s2=mosh-server
if [[ "$s1" == "$s2" ]]; then source .moshrc; fi
If called by mosh-server, bash will execute whatever it finds in $HOME/.moshrc - so just put your commands in a file named .moshrc in your home directory.
Because mosh invokes a login shell, you should have a line
source .bashrc
in your .bash_profile, or put the above lines in .bash_profile.