The git hook provided will check the files which are to be committed via Code Sniffer and rejects the commit if it finds violations.
The easiest way to install the hook is to link the pre-commit file to your .git/hooks folder of your project:
# Ensure that the hook is executable:
chmod +x pre-commit
# create a symbolic link
ln -s $(pwd)/pre-commit /path/to/your/project/.git/hooks/
Of course you can copy the hook file to your .git/hooks folder instead of linking it. But in this case you would manually have to update the file when the original in this project changes.
There is a template for a config file config.dist which you can copy to config and edit to your liking.
The use of your own config file is purely optional. The hook works out of the box with sensible defaults.
By default the hook is configured to run PHP Code Sniffer on the full content of the changed files. You can set the config parameter PHPCS_CHANGED_LINES_ONLY=1 in the config file to report only on coding style violations found in the changed lines.
To achieve this we make use of the coverageChecker project as PHP Code Sniffer is not capable of doing it itself. The needed dependency is installed with composer along with Code Sniffer.
Please note that the output of PHP Code Sniffer and the coverageChecker differ. It is not possible to unify the output at the moment.
By default the hook also runs the "gherkinlint" grunt task (if it is installed) on the changed files. So if you have any new or modified .feature files in your commit the hook won't let you commit unless you have fixed those linting issues.
To disable this check you can set BEHAT_RUN_LINT=0 in your config file.