Git hooks

Git hooks are a special git feature that allow for script execution when some particular event is fired, they can be useful to automate some development operation needed to start the actual work (update dev environment, setup packages,ecc…) or as a very simple update system for software deployed directly as a git repo (see my personal dotfiles for reference).

To create a git hook create a script with the name of the event that should fired the script inside the .git/hooks directory, script are executed from the root dir of the git repository, some examples are already put there by git.

ls .git/hooks/
post-commit

How to check if a file has changed #

In order to run hooks only when specific files are modified git CLI can be used, here and example with the post-commit hook

#!/bin/bash
# Redirect output to stderr.
exec 1>&2
# check if last commit contains something that has notes in the name
INCLUDED=notes
if git diff --name-only HEAD HEAD~1 | grep "$INCLUDED"; then
# do something
else
  echo "no $INCLUDED modified, nothing to do"
fi

Manage updates by triggering actions on pull #

The best hook for triggering actions on pull is the post-merge hook, this can be useful when deploying git repos to production and the update procedure need to track run some commands, this solution is suitable only for small projects, in large environments this method is likely to cause more problems that avoid extra work.

For example my personal dotfiles repo, update is managed trough a git hook created at installation time that runs the installation script at when a git merge event is fired

installation script

# ......
function configure_hook(){
  # create default monitor configuration file if does not exists
  if [[ ! -e ".git/hooks/post-merge" ]]; then
    echo 'create post-merge hook'
    echo  -e "#!/bin/bash\n./scripts.sh" > ".git/hooks/post-merge"
  fi
  chmod +x ".git/hooks/post-merge"
}
# ......

git post merge hook that is created

#!/bin/bash
./scripts.sh