Git hook to reject commits where files contain a specific string

Question

I am using Guard with Rspec; I use focus: true to force it run only tests I am working on. But sometimes I forget to remove focus: true and it is causing distraction for my future self and people I work with.

I want to make a git hook that would check the spec folder to make sure there is no focus: true in test files apart from spec/rails_helper.rb and keep it in Repository.

I have read this answer Putting git hooks into repository, guess it has to be a bit awkward.

How are hooks used to prevent a commit based on the contents of files?

Update

Here is what I have now but it doesn't work, even if there is no match, git refuses to commit.

FILES_PATTERN='\.rb(\..+)?$'
FORBIDDEN="(\, focus: true|binding\.pry)"
git diff --cached --name-only | egrep "$FILES_PATTERN" | xargs egrep --with-filename -n "$FORBIDDEN" && echo "Commit reject, found $FORBIDDEN reference, please remove" && exit 1
exit 0

Answer 1

A good source of information is the book at git-scm.

You want the pre-commit hook. To return a non-zero value (and thus abort the commit), you'd want something along these lines:

FILES_PATTERN='\.rb(\..+)?$'
FORBIDDEN='focus: true'
git diff --cached --name-only | \
  grep -spec/ | \
  grep -E $FILES_PATTERN | \
  xargs grep --with-filename -n $FORBIDDEN && echo "COMMIT REJECTED Found '$FORBIDDEN' references. Please remove them before commiting" && exit 1

That's lifted from this rather good tips site. I haven't tested the tweaks I made.