This is a one liner to get into vagrant, run a command, and when that command exits, keep your SSH session up and running rather than terminating.
I learned how to do this thanks to this StackOverflow article.
You could easily turn this command into a shell alias.
(cd ~/wherever/you/want && vagrant ssh -- -t 'mongo; exec bash --login')
That example above
cds to the vagrant directory, uses
ssh to open a terminal, runs
mongo, and when the mongo command terminates, it starts a new shell.
What this does is save us a little hassle. We can run some alias like
vagrant-mongo, and if we ever kill that command, we don't have to reconnect to the guest machine.
Not an incredible savings, but a convenience all the same.