Smash

Change the state of the universe, from <200 lines of bash!

Introduction

I liked terraform, but I wanted to be evil and use the full power of bash. 👺

Using simple scripts, determine system state and create plans to change it.

usage: smash [-anpst] [-o action,..]
  -o Only run comma seperated list of actions.
  -p Plan only; generate an execution plan. Can be approved in PR.
  -a Apply only; ensure state has not changed, and execute plan.
  -n Dry run; print the commands that would be executed, but do not execute them.
  -s Silent operation; do not print to stdout as they are executed.
  -t Output planned tests in tap format.

Lets create a simple smash action to install your dotfiles!

# Create an action directory
mkdir -p smash/install_mac

echo '
#!/bin/bash

# We are going to need a script to install your dotfiles
git clone https://github.com/username/dotfiles.git ~/.dotfiles
' > install.sh

echo '
#!/bin/bash

# Another to determine if dotfiles are installed
echo "DOTFILES_INSTALLED=$(test -d ~/.dotfiles && echo true)"
' > smash/install_mac/state

echo '
#!/bin/bash

# Use that context to plan what must be done to install your dotfiles
if [[ "$DOTFILES_INSTALLED" != "true" ]]; then
  echo "run bash ./install.sh"
fi

# You could optionally add unit tests
echo "test [[ -d ~/.dotfiles ]] || exit 1"
' > smash/install_mac/state

# Make them all executablable
chmod +x ./smash/install_mac/* ./install.sh

# Test your action with a dry run first.
smash -n
# Create a plan
smash -p
# Review plan
cat ./smash/engine/plan
# Apply plan
smash -a

# Or dont be a Becky...
smash

$ smash
==> init
$ smash/install_mac/state
DOTFILES_INSTALLED=
==> plan
$ smash/install_mac/plan
run bash ./install.sh
test [[ -d /Users/anthony/.dotfiles ]]
==> run
$ bash ./install.sh
git clone https://github.com/username/dotfiles.git /Users/anthony/.dotfiles
==> test
$ [[ -d /Users/anthony/.dotfiles ]]
==> done

$ echo $? # winning
0

And you can write these scripts in any language your heart desired!

Installation methods

source

sudo curl -L --fail \
  https://raw.githubusercontent.com/expelledboy/smash/master/smash.sh \
  -o /usr/local/bin/smash
sudo chmod +x /usr/local/bin/smash

docker

docker run --rm -it -v "${PWD}:/code" expelledboy/smash:latest -o make_target

Guide

• Your actions must be directories installed in ./smash/<action>
  • A smash action needs only one file ./smash/<action>/plan
  • Actions can contribute to state in ./smash/<action>/state
  • By default all actions in ./smash/* are run unless you use the -o option
    • Actions prefixed with undo_ are always ignored and must use -o
• State is ENV vars printed to stdout by the state script in .env format
  • eg. MY_VAR=useful_info
• These environment variables will be available in all phases of smash
• There are quite afew phases of smash;
  • state
  • plan
  • setup
  • run
  • test
• You can hook into setup, run and test
  • There are also pre and post hooks eg. pre-plan plan post-plan
  • Create a hook by printing to stdout in the plan script <hook> cmd args
• You can create global util scripts in ./smash/scripts/*
  • These will be available in all phases
• You can commit ./smash/engine/* files as part of CI/CD review process

Rollbacks

Its important understand that actions push your system towards a desired state. Rather than supporting undo functionality in smash actions my feeling is it would be preferred to create actions that achieve the opposite desired state. You can read previous system states in the ./smash/engine/state.* files during planning which provides maximum flexibility.

Interesting side effects which fell out of the design was toggling.

$ smash.sh -s -o make_target,undo_make_target && ls ./target
==> done
version

$ smash.sh -s -o make_target,undo_make_target && ls ./target
==> done
ls: ./target: No such file or directory

$ smash.sh -s -o make_target,undo_make_target && ls ./target
==> done
version

Contributions

If you want to change behavior please create a unit test in ./test.sh.

Otherwise I welcome changes early in the development of this project!