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Smoosh (the Symbolic, Mechanized, Observable, Operational SHell) is a formalization of the POSIX shell standard; Smoosh is one part of Michael Greenberg's broader project on the POSIX shell.

Smoosh is written in a mix of Lem and OCaml, using libdash to parse shell code.


There are two ways to work with Smoosh: virtually (in a Vagrant VM or in a Docker container) or natively. Because Smoosh depends on many parts and specific versions of some libraries, it may be easier to install via a VM or Docker.

Building Smoosh natively

To install Smoosh directly on your computer, you will need to manually configure your system with the dependencies listed in .github/workflows/build.yml. In particular:

  • A C toolchain
  • Autoconf, autotools, libtool, pkg-config, libffi, and libgmp (on macOS, this may be called glibtoolize, e.g., run brew install libtool)
  • OPAM (well sourced, i.e., eval $(opam env))
  • Ruby and Ruby bundler (for the web server)

Once you have those dependencies, you should be able to crib from .travis.yml:

$ git clone --recurse-submodules
Cloning into 'smoosh'...
... [lots of fetching] ...
Submodule path 'libdash': checked out 'yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy'
Submodule path 'modernish': checked out 'zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz'
$ cd smoosh
$ opam install -y ocamlfind ocamlbuild num zarith extunix lem
$ (cd libdash; opam pin -y add .)
$ make -C src all all.byte
$ export PATH="$(pwd)/src:$PATH"

Thanks to @idkjs for documenting a macOS build.

Building Smoosh in a Vagrant VM

In a system with Vagrant, you should be able to download the Smoosh VM image from the Vagrant Cloud service (~1.3GB):

~$ mkdir smoosh; cd smoosh
~/smoosh$ vagrant init mgree/smoosh --box-version 0.1.1
~/smoosh$ vagrant up
Bringing machine 'default' up with 'virtualbox' provider...
==> default: Box 'mgree/smoosh' could not be found. Attempting to find and install...
    default: Box Provider: virtualbox
    default: Box Version: 0.1.1
==> default: Loading metadata for box 'mgree/smoosh'
    default: URL:
==> default: Adding box 'mgree/smoosh' (v0.1.1) for provider: virtualbox
    default: Downloading:
~/smoosh$ vagrant ssh
vagrant@debian9:~$ cd smoosh

You are now in a directory where you can run tests. The smoosh executable should be on your path in any case.

Building Smoosh in Docker

To build via Docker, you merely need to fetch the Smoosh repo and its submodules. The script in the base of the repo will invoke the appropriate Docker commands.

$ git clone --recurse-submodules
Cloning into 'smoosh'...
... [lots of fetching] ...
Submodule path 'libdash': checked out 'yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy'
Submodule path 'modernish': checked out 'zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz'
$ cd smoosh
$ ./
... [long docker build] ...
Successfully tagged smoosh:latest
... [tests build] ...
Successfully tagged smoosh-test:latest
... [tests run] ...

smoosh v0.1 (build YYYY-MM-DD_HH:MM)

... [more docker builds] ...
Successfully tagged smoosh-web:latest

If the build process was successful, there are now two tagged Docker images, which can be run interactively via docker run -it [image tag]. The two images are:

  • smoosh, a Docker environment with Smoosh installed as /bin/smoosh
  • smoosh-test, an extension of the smoosh image with unit and system tests

Running tests using the Docker image

  • To run the test suite after building, run: docker build -t smoosh-test -f Dockerfile.test . && docker run smoosh-test
  • To explore the built image, run: docker run -it smoosh

To test by hand, there are three sets of relevant tests: the libdash tests (in libdash/test), the unit tests for symbolic smoosh (in src), and the shell test suite (in tests). All three directories have Makefiles with appropriate test targets, so you can test both by running the following:

$ docker run -it smoosh-test
opam@XXXXXXXXXXXX:~$ make -C libdash/test test
opam@XXXXXXXXXXXX:~$ make -C src/ test
opam@XXXXXXXXXXXX:~$ make -C tests test

Using the Shtepper

The Shtepper is a web-based visualization tool for symbolically running POSIX shell scripts. While available online, you can also run a local version of the Shtepper using the smoosh-web Docker image. To start the local Shtepper, you must build the web interface first. Run, from the smoosh repo root:

$ docker build -t smoosh-web -f Dockerfile.web .
$ docker run -p 80:2080 --name smoosh-web -t smoosh-web
Thin web server (v1.7.2 codename Bachmanity)
Maximum connections set to 1024
Listening on, CTRL+C to stop

You can then navigate to http://localhost/ in your web browser of choice. The Shtepper should work in any web browser, but has only undergone extensive testing in Firefox.

Running tests

However you've installed Smoosh, you can run the tests by going to the appropriate Smoosh directory (the home directory in Docker; ~/smoosh in a Vagrant VM). There are three sets of local Smoosh tests: libdash parser tests, unit tests, and system tests. You can run them in one go as follows:

vagrant@debian9:~/smoosh$ make -C libdash/test test && make -C src test && make -C tests
make: Entering directory '/home/vagrant/smoosh/libdash/test'
ocamlfind ocamlopt -g -package dash,ctypes,ctypes.foreign -linkpkg -o test.native
ocamlfind ocamlcp -p a -package dash,ctypes,ctypes.foreign -linkpkg -o test.byte
TESTING test.native
tests/ OK
tests/builtin.trap.exitcode.test OK
tests/ OK
tests/empty_case OK
tests/escaping OK
tests/ OK
tests/ OK
tests/ OK
tests/redir_indirect OK
tests/ OK
tests/ OK
tests/ OK
tests/syntax OK
tests/ OK
tests/tilde_arith OK
tests/timeout3 OK
TESTING test.byte
tests/ OK
tests/builtin.trap.exitcode.test OK
tests/ OK
tests/empty_case OK
tests/escaping OK
tests/ OK
tests/ OK
tests/ OK
tests/redir_indirect OK
tests/ OK
tests/ OK
tests/ OK
tests/syntax OK
tests/ OK
tests/tilde_arith OK
tests/timeout3 OK
make: Leaving directory '/home/vagrant/smoosh/libdash/test'
make: Entering directory '/home/vagrant/smoosh/src'

=== Initializing Dash parser...
=== Running evaluation tests...
=== ...ran 229 evaluation tests with 0 failures.

=== Running word expansion tests...
=== ...ran 64 word expansion tests with 0 failures.

=== Running path/fs tests...
=== ...ran 27 path/fs tests with 0 failures.

=== Running arithmetic tests...
=== ...ran 253 arithmetic tests with 0 failures.

make: Leaving directory '/home/vagrant/smoosh/src'
make: Entering directory '/home/vagrant/smoosh/tests'
== Running shell tests ===============================================
...................... 162/162 tests passed
make: Leaving directory '/home/vagrant/smoosh/tests'

The unit tests are run directly via a binary, smoosh/src/runtest; the system tests use the Makefile in the smoosh/tests directory. These system tests are shell scripts paired with expected STDOUT, STDERR, and exit statuses.

Running tests on another shell

Both the Docker image and Vagrant VM will have other shells installed. The versions are nearly the same as those mentioned in the paper, but may have changed slightly due to rolling releases. (Numbers may therefore differ slightly.)

Shell Version
dash 0.5.8-2.4
bash 4.4-5
yash 2.43-1
zsh 5.3.1-4+b3
ksh 93u+20120801-3.1
mksh 54-2+b4

You can run the system tests on any shell by setting TEST_SHELL. Some shells may not terminate on all tests; you may need to run make clean while changing tests.

vagrant@debian9:~/smoosh$ TEST_SHELL=dash make -C tests

To get more detail on test failures, you should set the TEST_DEBUG variable, e.g.:

vagrant@debian9:~/smoosh$ TEST_DEBUG=1 TEST_SHELL=dash make -C tests

Running Modernish's tests/shell diagnostic

To run the Modernish tests, you must go to smoosh/modernish and simulate an install as follows:

vagrant@debian9:~/smoosh/modernish$ yes n | ./ -s smoosh
Relaunching with /home/mgree/.local/bin/smoosh...
* Modernish version 0.15.2-dev, now running on /home/mgree/.local/bin/smoosh.
* This shell identifies itself as smoosh version 0.1.
  Modernish detected the following bugs, quirks and/or extra features on it:
... [weird noise on native Linux/VM; crash in Docker] ...
* Running modernish test suite on /home/mgree/.local/bin/smoosh ...
* lib/modernish/tst/@sanitychecks.t 
  002: ASCII chars and control char constants   - FAIL
* WARNING: modernish has some bug(s) in combination with this shell.
           Run 'modernish --test' after installation for more details.
Are you happy with /home/mgree/.local/bin/smoosh as the default shell? (y/n) Aborting.

To test another shell, run yes n | smoosh/modernish/ -s [shell name].

NB that the HDOCMASK bug seems to appear only in Linux and not on macOS.

POPL 2020 Artifact Evaluation

What can be reproduced from the Smoosh paper?

  • You should be able to build Smoosh on any computer that supports Docker.

  • The built Smoosh should pass all of its unit and system tests.

  • You should be able to run the Smoosh system tests on other shells. Due to rolling releases, your environment may have slightly different shell versions (which may then pass a different number of tests).

What can not be reproduced from the Smoosh paper?

  • The POSIX test suite cannot be distributed, so we cannot reproduce those tests. We do, however, have permission to distribute the resulting journals from running the test suite. Look in smoosh/posix-journals.

  • As of 2019-10-21, Modernish under virtualization (whether in Docker or in a Vagrant VM) exposes a bug in Smoosh's interaction with the dash parser. This bug wasn't poked when running on macOS.

    The manifestations are different: in Docker, Smoosh crashes with a 'broken DEFPATH' error; in a VM, some backtraces appear but the Modernish diagnostic completes with the correct output (just BUG_MULTIBYTE).

    Modernish should still complete without a problem on macOS, but I'm unable to test this (as my Mac is not booting).