mjhjmtu

I regularly ssh on several different servers, some of which don't have fish installed, but many do. I'd like to get fish as shell if available (changing midway is always tedious, and you lose the history of what you already typed), but changing the default shell is not a good idea, as:

• there are many different machines that I would need to change;


• on many other I'm logged in through LDAP, and changing my shell as stored on LDAP would break on machines where fish is not available;


• in general, as fish is not POSIX-sh compatible putting it as default shell may break commands executed by scripts through ssh;


• finally, there are a few machines where the user is shared with other people (or, where I have to login another user), so changing the default shell is not a good idea.

So, ideally I'd like to have a command like ssh that automagically starts fish if available, or just leave whatever default shell is provided otherwise.

After some experiments, I put together the fissh script:

#!/bin/sh
ssh "$@" -t "sh -c 'if which fish >/dev/null ; then exec fish; else exec $SHELL; fi'"

• 
  "$@" forwards all arguments passed to ssh
  


• 
  -t forces the allocation of a tty (otherwise ssh defaults to no tty when a command is specified)


• 
  sh -c is required because we don't know what shell we may have on the other side - on my personal machines I do have fish as default shell;


• 
  which fish succeeds if it finds an executable fish; in that case, it is exec-ed;


• otherwise, we fall back to $SHELL, which is the default shell for the current user ($ is escaped otherwise it gets expanded by sh "on this side").

Notice that stdout of which is hidden (as in the normal case we don't care about where fish was found), but stderr (where the error message that fish couldn't be found) is intentionally left intact as a warning to the user that, despite our best intentions, fish couldn't be found.

To complete the experience, on my machines with fish I add the support for customized completion by creating a ~/.config/fish/completions/fissh.fish file containing

complete -c fissh -w ssh

to instruct fish that fissh has the exact same valid completions as ssh.