Overcommit

Dependencies

Some hooks have third-party dependencies. For example, to lint your SCSS files, you’re going to need the scss_lint gem.

Depending on the hooks you enable/disable for your repository, you’ll need to ensure your development environment already has those dependencies installed. Most hooks will display a warning if a required executable isn’t available.

If you are using Bundler to manage your Ruby gem dependencies, you’ll likely want to use the gemfile option to control which gem versions are available during your hook runs.

Automatically Install Overcommit Hooks

If you want to use overcommit for all repositories you create/clone going forward, add the following to automatically run in your shell environment:

export GIT_TEMPLATE_DIR="$(overcommit --template-dir)"

The GIT_TEMPLATE_DIR provides a directory for Git to use as a template for automatically populating the .git directory. If you have your own template directory, you might just want to copy the contents of overcommit --template-dir to that directory.

Skipping Hooks

Sometimes a hook will report an error that for one reason or another you’ll want to ignore. To prevent these errors from blocking your commit, you can include the name of the relevant hook in the SKIP environment variable, e.g.

SKIP=RuboCop git commit

If you would prefer to specify a whitelist of hooks rather than a blacklist, use the ONLY environment variable instead.

ONLY=RuboCop git commit

Use this feature sparingly, as there is no point to having the hook in the first place if you’re just going to ignore it. If you want to ensure a hook is never skipped, set the required option to true in its configuration. If you attempt to skip it, you’ll see a warning telling you that the hook is required, and the hook will still run.

Disabling Overcommit

If you have scripts that execute git commands where you don’t want Overcommit hooks to run, you can disable Overcommit entirely by setting the OVERCOMMIT_DISABLE environment variable.

OVERCOMMIT_DISABLE=1 ./my-custom-script

Disabling Colorized Output

Overcommit automatically colorizes its output based on whether it is outputting to a TTY. However, you can manually enable/disable color by setting the OVERCOMMIT_COLOR environment variable.

OVERCOMMIT_COLOR=0 git commit

Continuous Integration

You can run the same set of hooks that would be executed in a pre-commit hook against your entire repository by running overcommit --run. This makes it easy to have the checks verified by a CI service such as Travis CI, including custom hooks you’ve written yourself.

The --run flag works by creating a pre-commit context that assumes all the files in your repository have changed, and follows the same rules as a normal pre-commit check. If any hook fails with an error, it will return a non-zero exit code.

Configuration

Overcommit provides a flexible configuration system that allows you to tailor the built-in hooks to suit your workflow. All configuration specific to a repository is stored in .overcommit.yml in the top-level directory of the repository.

When writing your own configuration, it will automatically extend the default configuration, so you only need to specify your configuration with respect to the default. In order to enable/disable hooks, you can add the following to your repo-specific configuration file:

PreCommit:
  RuboCop:
    enabled: true
    command: ['bundle', 'exec', 'rubocop'] # Invoke within Bundler context

Additionally, you may wish to have repo-specific configurations that are local to your computer that are not part of the shared repo config. Adding a .local-overcommit.yml file in the top-level directory of the repository adds another configuration file. This file works the same as .overcommit.yml. Adding this to ignored files in a git repo will allow you to have a local configuration per repo.

Hook Categories

Hook configurations are organized into categories based on the type of hook. So pre-commit hooks are located under the PreCommit option, and post-commit hooks are located under PostCommit. See the default configuration for a thorough example.

The `ALL` Hook

Within a hook category, there is a special type of hook configuration that applies to all hooks in the category. This configuration looks like a normal hook configuration, except it has the name ALL:

PreCommit:
  ALL:
    problem_on_unmodified_line: warn
    requires_files: true
    required: false
    quiet: false

  SomeHook:
    enabled: true

  ...

The ALL configuration is useful for when you want to DRY up your configuration, or when you want to apply changes across an entire category of hooks.

Note that array configuration options (like include/exclude) in the special ALL hook section are not merged with individual hook configurations if custom ones are defined for the hook. Any custom configuration option for include/exclude will replace the ALL hook’s configuration. If you want to have a global list of default exclusions and extend them with a custom list, you can use YAML references, e.g.

PreCommit:
  ALL:
    exclude: &default_excludes
      - 'node_modules/**/*'
      - 'vendor/**/*'
  MyHook:
    exclude:
      - *default_excludes
      - 'another/directory/in/addition/to/default/excludes/**/*'

Again, you can consult the default configuration for detailed examples of how the ALL hook can be used.

Gemfile

You may want to enforce the version of Overcommit or other gems that you use in your git hooks. This can be done by specifying the gemfile option in your .overcommit.yml.

The gemfile option tells Overcommit to load the specified file with Bundler, the standard gem dependency manager for Ruby. This is useful if you would like to:

Enforce a specific version of Overcommit to use for all hook runs (or to use a version from the master branch that has not been released yet)
Enforce a specific version or unreleased branch is used for a gem you want to use in your git hooks

Loading a Bundler context necessarily adds a startup delay to your hook runs as Bundler parses the specified Gemfile and checks that the dependencies are satisfied. Thus for projects with many gems this can introduce a noticeable delay.

The recommended workaround is to create a separate Gemfile in the root of your repository (call it .overcommit_gems.rb), and include only the gems that your Overcommit hooks need in order to run. Generate the associated lock file by running:

bundle install --gemfile=.overcommit_gems.rb

…and commit .overcommit_gems.rb and the resulting .overcommit_gems.rb.lock file to your repository. Set your gemfile option to .overcommit_gems.rb, and you’re all set.

Using a smaller Gemfile containing only the gems used by your Overcommit hooks significantly reduces the startup delay in your hook runs. It is thus the recommended approach unless your project has a relatively small number of gems in your Gemfile.

Plugin Directory

You can change the directory that project-specific hooks are loaded from via the plugin_directory option. The default directory is .git-hooks.

Quiet Hook Runs

If you prefer to have your hooks be completely silent unless there is a problem, you can set the top-level quiet option to true. Note that if you have many hooks or slow hooks this may not be desirable, as you don’t get visual feedback indicating the general progress of the hook run.

Concurrency

Overcommit runs hooks in parallel by default, with a number of concurrent workers equal to the number of logical cores on your machine. If you know your particular set of hooks would benefit from higher/lower number of workers, you can adjust the global concurrency option. You can define single-operator mathematical expressions, e.g. %{processors} * 2, or %{processors} / 2.

concurrency: '%{processors} / 4'

Note that individual hooks can specify the number of processors they require with the processors hook option. See the hook options section for more details.

Signature Verification

You can disable manual verification of signatures by setting verify_signatures to false. See the Security section for more information on this option and what exactly it controls.

CommitMsg

commit-msg hooks are run against every commit message you write before a commit is created. A failed hook prevents a commit from being created. These hooks are useful for enforcing policies on your commit messages, e.g. ensuring a task ID is included for tracking purposes, or ensuring your commit messages follow proper formatting guidelines.

PostCheckout

post-checkout hooks run after a successful git checkout, or in other words any time your HEAD changes or a file is explicitly checked out.

PostCommit

post-commit hooks run after a commit is successfully created. A hook failing in this case does not prevent the commit since it has already occurred; however, it can be used to alert the user to some issue.

PostMerge

post-merge hooks run after a git merge executes successfully with no merge conflicts. A hook failing in this case does not prevent the merge since it has already occurred; however, it can be used to alert the user to some issue.

PostRewrite

post-rewrite hooks run after a commit is modified by a git commit --amend or git rebase. A hook failing in this case does not prevent the rewrite since it has already occurred; however, it can be used to alert the user to some issue.

PreCommit

pre-commit hooks are run after git commit is executed, but before the commit message editor is displayed. If a hook fails, the commit will not be created. These hooks are ideal for syntax checkers, linters, and other checks that you want to run before you allow a commit to even be created.

PrePush

pre-push hooks are run during git push, after remote refs have been updated but before any objects have been transferred. If a hook fails, the push is aborted.

PreRebase

pre-rebase hooks are run during git rebase, before any commits are rebased. If a hook fails, the rebase is aborted.

MergedCommits

Repo-Specific hooks

Out of the box, overcommit comes with a set of hooks that enforce a variety of styles and lints. However, some hooks only make sense in the context of a specific repository.

For example, you can have a number of simple checks that run against your code to catch common errors. For example, if you use RSpec, you can make sure all spec files contain the line require 'spec_helper'.

Inside our repository, we can add the file .git-hooks/pre_commit/ensure_spec_helper.rb in order to automatically check our spec files:

module Overcommit::Hook::PreCommit
  class EnsureSpecHelper < Base
    def run
      errors = []

      applicable_files.each do |file|
        if File.read(file) !~ /^require 'spec_helper'/
          errors << "#{file}: missing `require 'spec_helper'`"
        end
      end

      return :fail, errors.join("\n") if errors.any?

      :pass
    end
  end
end

The corresponding configuration for this hook would look like:

PreCommit:
  EnsureSpecHelper:
    enabled: true
    description: 'Checking for missing inclusion of spec_helper'
    include: '**/*_spec.rb'

Adding Existing Git Hooks

You might already have hook scripts written which you’d like to integrate with Overcommit right away. To make this easy, Overcommit allows you to include your hook script in your configuration without writing any Ruby code. For example:

PostCheckout:
  CustomScript:
    enabled: true
    required_executable: './bin/custom-script'

So long as a command is given (either by specifying the command option directly or specifying required_executable) a special hook is created that executes the command and appends any arguments and standard input stream that would have been passed to the regular hook. The hook passes or fails based on the exit status of the command.

The script is executed as if Git were calling the hook directly. If you want to understand which arguments are passed to the script depending on the type of hook, see the git-hooks documentation.

Security

While Overcommit can make managing Git hooks easier and more convenient, this convenience can come at a cost of being less secure.

Since installing Overcommit hooks will allow arbitrary plugin code in your repository to be executed, you expose yourself to an attack where checking out code from a third party can result in malicious code being executed on your system.

As an example, consider the situation where you have an open source project. An attacker could submit a pull request which adds a post-checkout hook that executes some malicious code. When you fetch and checkout this pull request, the post-checkout hook will be run on your machine, along with the malicious code that you just checked out.

Overcommit attempts to address this problem by storing a signature of your configuration and all hook plugin code since the last time it ran. When the signature changes, a warning is displayed alerting you to which plugins have changed. It is then up to you to manually verify that the changes are not malicious, and then continue running the hooks.

The signature is derived from the contents of the plugin’s source code itself and any configuration for the plugin. Thus a change to the plugin’s source code or your local repo’s .overcommit.yml file could result in a signature change.

Community

All major discussion surrounding Overcommit happens on the GitHub issues list.

Changelog

If you’re interested in seeing the changes and bug fixes between each version of overcommit, read the Overcommit Changelog.