Command to know Rails project root from shell script - ruby-on-rails

Question

Is there any obvious command (be it a rails command, rake command, or other) that I can use to get the path to the root of a rails project from within a shell script?
Context:
I'm writing a shell script. I'm going to execute that script from an arbitrary directory inside a rails project, and the script needs to determine the absolute path of the rails project root.
So, for example, if the script were
#!/bin/bash
rails_root=# get the root somehow...
and given that the root directory of my project is
/home/myuser/projects/myrailsapp
then I should be able to place that script in
/home/myuser/projects/myrailsapp/scripts/myscript
and call it from elsewhere in the project
cd /home/myuser/projects/myrailsapp/app/assets
../../scripts/myscript
and the script should be able to know the path of the root directory.
I've come up with two different ways of solving this problem:
#!/bin/bash
rails_root=$(rake about | grep 'Application root' | sed 's/Application root[ ]*//')
#!/bin/bash
rails_root=$(rails c <<-EORUBY | grep ^rails_root_is | sed 's/rails_root_is//'
puts "rails_root_is#{Rails.root}"
EORUBY
)
But I feel like there should be a more obvious way to do this. I was expecting to use an existing command.

Answer 1

If you really need it to be in a shell, you could:
rails_root=rails runner -e development "puts Rails.root"|tail -1

Answer 2

Instead of a shell script you can use rake. Besides the simplicity of dealing with a high level language you also have full access to the rails environment and you don't have to deal with all the pitfalls and issues when dealing with shell scripts which should work across platforms and shells.
To generate a rake task from rails:
rails g task foo dosomething
Which would generate an a rakefile in lib/tasks/foo.rake. From the rake task you can access the Rails root directory though Rails.root.
namespace :foo do
desc "TODO"
task dosomething: :environment do
puts "Rails root is: #{ Rails.root }"
puts "Current working directory is: #{ Dir.pwd }"
# You can invoke the shell with backticks, exec or ...
puts "You are: " + `whoami`
end
end
A few good resources:
Jason Seifer: Rake Tutorial
6 Ways to Run Shell Commands in Ruby

Answer 3

Not as elegant as using rake, this is a recursive shell function that depends on identifying the Gemfile - kind of a hack but quite fast. There are several other ways to determine whether you have found the Rails root.
function rr () {
if test `pwd` = $HOME
then
echo not in Rails
elif test -f Gemfile && grep Rails Gemfile > /dev/null
then
pwd
else
(cd ..; rr)
fi
}