A single line REPL for your favorite languages & libraries. Built on Docker.

View the Project on GitHub vishnugopal/replr


A single line REPL for your favorite languages & libraries. Built on Docker.

This is currently usable & stable, and supports the ruby, python and node stacks.

See TODO for future work.


replr <stack> <libraries...>

So for a simple ruby REPL, including the chronic gem, it would be:

replr ruby chronic

Or for a python REPL, including the flask and requests packages, it would be:

replr python flask requests

You can also specify versions of stacks & libraries to install:

replr ruby:2.3.1 chronic:0.10.1 activesupport:5.1.0

That’s it! It’s very simple. Replr currently supports three stacks: ruby, python and node.


replr is built on Ruby and requires Ruby 2.5+ installed.

gem install replr

That’s it! replr should now be available in your $PATH.

More Commands

replr prune

will delete all docker images associated with replr. This saves space!

Contributing & Development

replr is built on Ruby and requires a Ruby 2.5+ installed to develop. It’s pretty easy to get started and add a stack, please see node’s implementation for a quick-start. There’s also a companion integration spec that tests expected behavior in node’s test suite that you should emulate and implement for every stack you make.

Most of the “scaffolding” around creating the REPL & dealing with docker’s implementation details have been abstracted away if you use the Replr::Stack::REPLMaker class, so you only need to implement stack-specific functionality. This includes:

Note: if you want to run the specs (built with minitest/spec), please do:

bundle exec rake test


replr uses docker to manage different stacks and installed libraries. It creates docker images that are tagged replr-<stack>-<libraries...> for each stack and library combo you initiate.

The first time you start a new stack & library combo, docker will take some time to spin up instances. Future executions of the same stack should be near-instant.

This is how a full output from a replr install will look like the first time you try out a new stack & library combo:

❯ replr ruby chronic
(1/25) Upgrading musl (1.1.14-r14 -> 1.1.14-r16)
(2/25) Installing gmp (6.1.0-r0)
(3/25) Installing libgcc (5.3.0-r0)
(4/25) Installing libstdc++ (5.3.0-r0)
(5/25) Installing libgmpxx (6.1.0-r0)
(6/25) Installing gmp-dev (6.1.0-r0)
(7/25) Installing libedit (20150325.3.1-r3)
(8/25) Installing ruby-libs (2.3.7-r0)
(9/25) Installing ruby-dev (2.3.7-r0)
(10/25) Installing binutils-libs (2.26-r1)
(11/25) Installing binutils (2.26-r1)
(12/25) Installing isl (0.14.1-r0)
(13/25) Installing libgomp (5.3.0-r0)
(14/25) Installing libatomic (5.3.0-r0)
(15/25) Installing mpfr3 (3.1.2-r0)
(16/25) Installing mpc1 (1.0.3-r0)
(17/25) Installing gcc (5.3.0-r0)
(18/25) Installing make (4.1-r1)
(19/25) Installing musl-dev (1.1.14-r16)
(20/25) Installing libc-dev (0.7-r0)
(21/25) Installing fortify-headers (0.8-r0)
(22/25) Installing g++ (5.3.0-r0)
(23/25) Installing build-base (0.4-r1)
(24/25) Installing build-dependencies (0)
(25/25) Upgrading musl-utils (1.1.14-r14 -> 1.1.14-r16)
1 gem installed
Fetching gem metadata from
Installing chronic 0.10.2
Bundle complete! 1 Gemfile dependency, 2 gems now installed.
Gems in the groups development and test were not installed.
Bundled gems are installed into `/usr/local/bundle`

The next time, it’s much cleaner:

❯ replr ruby chronic
irb(main):001:0> Chronic.parse("tomorrow")
=> 2018-08-25 12:00:00 +0000

As you can see, replr tries its best to abstract away the underlying docker installation. You shouldn’t have to worry about Dockerfile & so on just to get a REPL!

It also tries its best to make sure libraries you mention are auto-required in the REPL, so you don’t have to do any additional work!