SSH – Execute Commands Before Interactive Mode

ssh

When starting ssh session with ssh command I seem to have two options – default interactive session with default env and starting from home directory – or to execute arbitrary command but non-interactively (even tricks like ssh "command; command; bash -i -l" don't seem to do much good). Quite often I want interactive session, but with something happening before that – normally a directory change, or sometimes system environment adjustment. These things would vary from session to session, so I cannot just stick them into .bashrc or so.

Is there any way to make that happen?

Best Answer

I'm self-answering, as I've finally discovered the secret. Neither -t option for ssh, nor -l option for bash will lead to login shell on their own - but in combination they work.

ssh user@host.com -t 'cd /some/where; FOO=BAR NUMBER=42 bash -l' changes directory, sets environment variables, and then starts proper login shell (the only difference I've found so far is that /etc/motd isn't displayed this way - it's normally ssh's or login's responsibility, not bash's - other than that everything seems to work perfectly, and all environmental variables are identical).

These environment / directory changes happen after ssh, so they're not restricted by PermitUserEnvironment and related settings (exactly as planned), but before .bashrc/.profile get executed. This has upsides and downsides - it is harder to just override something that gets set from bash init scripts like PS1, but easier to pack exactly the right values into ssh command lines, and have .profile do all the heavy lifting.

And if really necessary, it's actually pretty easy to get bash to execute something after .profile with command line like ssh user@foo.com -t 'cd /mnt; echo ". ~/.bash_profile; PS1=\"\\h-\w \"" >~/xxx; bash --init-file ~/xxx' - very ugly when put that way, but these alternative .profile files can be prepared before. (as far as I can tell bash has a few candidate locations for .profile script and will execute the first one found - . file doesn't have such automatic fallbacks, so you'll need to check where's your normal profile if you want to do that)

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