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Jochen Lillich
Jochen Lillich

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An easy and secure way to launch helper scripts in a project

On one of my recent live coding streams, a viewer asked what my abe script does. I showed that it simply launched a Ruby command in my project’s application container. Since I’m using Docker Compose to spin up most of my development environments, I have to run all development tasks within the application container. Typing abe rake test is much faster than typing docker-compose exec app bundle exec rake test, so I added this script to my project’s bin directory:

docker-compose exec app bundle exec $@

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It’s a nifty time-saver, but the smart part of this isn’t the script itself but how I make helper scripts in the bin directory of my projects easy to launch without having to prepend every command with ./bin/.

If you’re familiar with how a Unix shell finds the right program to execute, you ‘ll probably suggest just adding ./bin to the environment variable PATH. But that’s a risky move because you don’t want to accidentally launch a malicious script after checking out a repository that happens to have an executable ls command in its bin directory.

Once again, it was the talented devs over at ThoughtBot who found a better solution. Instead of adding ./bin to PATH, they recommend adding .git/safe/../../bin. With this entry, the shell descends into .git, further down into safe, all the way back to the repository root and only then into bin. What makes this seemingly roundabout way to find your helper scripts secure is that it only works if you’ve first manually created the subdirectory safe within .git. The latter is, after all, git’s data directory which normally doesn’t contain a directory named safe.

There you have it — easy access to your project’s helper scripts is simple to achieve. And without any additional effort, it’s safe as well!

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