Pre-commit git hooks

Sometimes, we may need to run our services locally with a series of properties that we don’t want to accidentally commit to our repositories for being sensitive. Whilst looking for a solution to this problem, I came accross git’s hooks, and more particularly, pre-commit hooks. I know other people use them, for example, to make sure all of their commits are signed, and I can only imagine how many other uses they may have.

Today, I would like to share with you, in an easy way, how to use them.

Steps:

  1. First, you will need to decide if you’d like to keep these hooks to yourself or they will be committed and shared along the rest of the repo.
    • Local-only: Find the .git/hooks folder at the root of your repo (it will likely be hidden) and create a file called pre-commit, without any extensions. Make the file executable by running chmod + x .git/hooks/pre-commit from the root of your project. The .git folder is by default ignored by git and therefore, any changes you make inside it will only affect your local project.
    • Committed to repo: Create a new folder called .githooks (or anything you like, but we’ll use this as an example) and create a file called pre-commit inside it, without any extensions. Run the following command: git config --local core.hookspath .githooks/ to change where git looks for the hooks (make sure that you are not using any other hooks inside the .git folder, as this will change the configuration). If needed, you can also check where this configuration is pointing to by running git config -l and looking for the core.hookspath line, if it is not present, it defaults to .git. The folder and file we created can be commited later on if needed.
  2. Inside our pre-commit file, we will add the following script, which finds the files that have been staged in git, iterates through them and looks for a FORBIDDEN_STRING. If found, it aborts the commit and displays an error message that includes the name of the problematic file:
#!/bin/sh
FORBIDDEN_STRING="FORBIDDEN_STRING"

# Get a list of the modified files
FILES=$(git diff --cached --names-only)
for FILE in $FILES
  do
    if grep -q "$FORBIDDEN_STRING" $FILE
    then
      echo "Before committing, you must remove the added properties in the following file: $FILE"
      exit 1
  fi
done
  1. If you decided to commit the pre-commit hook to the repository, your colleagues would need to run the command git config --local core.hookspath .githooks/ to activate this feature.

And that is all for now, I hope you found it helpful and please let me know if you have any questions or feedback. See you soon, catonauts!

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