Jan 19, 2012 - 2 minute read - git blog jekyll

Abusing Git pre-commit hooks for fun and profit

So, git pre-commit hooks are executable files (yes, you have to declare them as chmod +x - for some reason I forget this every time I write hooks) that are run right before you commit. This type of stuff lets you verify that your application is working, run a few tests, etc before it gets committed. At least the current use case I have (that probably illustrates the point of this particular hook fairly well) is related to this website. So, as I started working on this, I realized that categories are implmented as user plugins which aren’t allowed by github-pages for security reasons. Since all I’m doing is generating a static website, that doesn’t really matter as long as I copy the categories directory to the root, right? Why not automate that shit?

First I wrote a script “./run_extensions” with

#!/bin/bash rvm use 1.9.2 bundle install bundle exec ejekyll cp -rf _site/categories . git add .

not too surprising - I initialize rvm environment (I have that set in both bash and zsh shells that I use but it’s better to be explicit), bundle install and bundle exec ejekyll commands install the dependencies declared in the Gemfile and then run the static website generation using Jekyll. Now that I have plugins goodness, I can copy the categories folder from _site and make sure everything is staged.

Now the next step would be to make the pre-commit hook itself. So, the pre-commit hook runs from the parent directory of .git folder itself and can be anything. I have a bash script. The location is .git/hooks/pre-commit

#!/bin/bash ./

after this, make sure to run chmod +x .git/hooks/pre-commit so that it’s executable. From now all, each commit is going to generate all the necessary categories structure.