We use this library at GitHub to detect blob languages, highlight code, ignore binary files, suppress generated files in diffs, and generate language breakdown graphs.

Linguist defines the list of all languages known to GitHub in a yaml file. In order for a file to be highlighted, a language and lexer must be defined there.

Most languages are detected by their file extension. This is the fastest and most common situation.

For disambiguating between files with common extensions, we first apply some common-sense heuristics to pick out obvious languages. After that, we use a statistical classifier. This process can help us tell the difference between, for example, .h files which could be either C, C++, or Obj-C.

Linguist::FileBlob.new("lib/linguist.rb").language.name #=> "Ruby"

Linguist::FileBlob.new("bin/linguist").language.name #=> "Ruby"

See lib/linguist/language.rb and lib/linguist/languages.yml.

The actual syntax highlighting is handled by our Pygments wrapper, pygments.rb. It also provides a Lexer abstraction that determines which highlighter should be used on a file.

The Language Graph you see on every repository is built by aggregating the languages of each file in that repository. The top language in the graph determines the project's primary language. Collectively, these stats make up the Top Languages page.

The repository stats API, accessed through #languages, can be used on a directory:

project = Linguist::Repository.from_directory(".")
project.language.name  #=> "Ruby"
project.languages      #=> { "Ruby" => 0.98, "Shell" => 0.02 }

These stats are also printed out by the linguist binary. You can try running linguist on the lib/ directory in this repository itself:

$ bundle exec linguist lib/
100%  Ruby

Checking other code into your git repo is a common practice. But this often inflates your project's language stats and may even cause your project to be labeled as another language. We are able to identify some of these files and directories and exclude them.

Linguist::FileBlob.new("vendor/plugins/foo.rb").vendored? # => true

See Linguist::BlobHelper#vendored? and lib/linguist/vendor.yml.

Not all plain text files are true source files. Generated files like minified js and compiled CoffeeScript can be detected and excluded from language stats. As an extra bonus, these files are suppressed in diffs.

Linguist::FileBlob.new("underscore.min.js").generated? # => true

See Linguist::Generated#generated?.

github.com is usually running the latest version of the github-linguist gem that is released on RubyGems.org.

But for development you are going to want to checkout out the source. To get it, clone the repo and run Bundler to install its dependencies.

git clone https://github.com/github/linguist.git
cd linguist/
bundle install

To run the tests:

bundle exec rake test

The majority of contributions won't need to touch any Ruby code at all. The master language list is just a YAML configuration file.

We try to only add languages once they have some usage on GitHub, so please note in-the-wild usage examples in your pull request.

Almost all bug fixes or new language additions should come with some additional code samples. Just drop them under samples/ in the correct subdirectory and our test suite will automatically test them. In most cases you shouldn't need to add any new assertions.

To update the samples.json after adding new files to samples/:

bundle exec rake samples

Sometimes getting the tests running can be too much work, especially if you don't have much Ruby experience. It's okay: be lazy and let our build bot Travis run the tests for you. Just open a pull request and the bot will start cranking away.

Here's our current build status, which is hopefully green: