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Last pushed: 4 months ago
Short Description
A command line tool to identify unused code.
Full Description


A command line tool to identify unused code.

"What kinds of projects can I used it on?"


Yes, literally anything.

It's probably best if you have a file generated from ctags it can read from
(it looks in .git, tmp, and the root directory for a tags file), but if
you have another way to pipe a bunch of
methods/functions/classes/modules/whatever in, that works too.

Right now, there are some special cases built in for Rails and Phoenix apps
(specifically, assumptions about what's fine to only have one reference to,
e.g. Controllers in Rails and Views in Phoenix), but it'll work on Rubygems,
Elixir packages, or anything else.

That said, be confident the code you're removing won't break your program.
Especially with projects built in Ruby, Elixir, or JavaScript, there are ways
to dynamically trigger or define behavior that may be surprising. A test suite
can help here, but still cannot determine every possible execution path.

Installing and Updating

Homebrew (Recommended)

You can install my formulae via Homebrew with brew tap:

brew tap joshuaclayton/formulae

Next, run:

brew install unused

This will install unused and its corresponding dependencies.

To update, run:

brew update
brew upgrade unused

Alternatively, you can install with Stack or by hand. Because it needs to compile, installation times may vary, but it's often several minutes.


If you already have Stack installed, ensure you have the latest list of

stack update

Verify Stack is using at least lts-6.0 when installing by checking the
global project settings in ~/.stack/global-project/stack.yaml.

Once that is complete, run:

stack install unused

This will install unused in the appropriate directory for Stack; you'll want
to ensure your $PATH reflects this.

Installing by hand

This project is written in Haskell and uses Stack.

Once you have these tools installed and the project cloned locally:

stack setup
stack install

This will generate a binary in $HOME/.local/bin; ensure this directory is in
your $PATH.

Install via Docker

Once Docker is installed, create a binary within your $PATH to run the

#!/usr/bin/env bash

docker run --rm -it -v $(pwd):/code joshuaclayton/unused unused $@

Note that, because Unused will be running inside of a virtual machine, it will
take longer to generate output than were you to install via
previously-mentioned methods.

Using Unused

unused attempts to read from common tags file locations (.git/tags,
tags, and tmp/tags).

In an application where the tags file exists, run:


If you don't have a tags file, you can generate one by running:

git ls-files | xargs ctags

If you want to specify a custom tags file, or load tokens from somewhere else,

cat .custom/tags | unused --stdin

To view more usage options, run:

unused --help


Ctags (and a corresponding workflow) isn't configured

Exuberant Ctags (or another tool that will generate a tags file, like
hasktags for Haskell projects) is required to use unused correctly;
however, the version of ctags that ships with OS X (/usr/bin/ctags) is an
older version won't work with many languages (that BSD version of ctags says
it "makes a tags file for ex(1) from the specified C, Pascal, Fortran, YACC,
lex, and lisp sources.")

Installation via Homebrew includes the ctags dependency. You can also run
brew install ctags by hand. If you're not on OS X, use your favorite package
manager and refer to the Exuberant Ctags site for download instructions.

Ctags manual run

If you're using ctags to generate a tags file prior to running unused and
don't have a workflow around automatically generating a tags file, run:

git ls-files | xargs ctags -f tmp/tags

This will take your .gitignore into account and write the tags file to
tmp/tags. Be sure to write this to a location that's ignored by git.

While this process allows a developer to get started, it requires remembering
to run this command before running unused. Let's explore how to automate this

Ctags automatic runs via git hooks

With ctags installed, you'll likely want to configure your workflow such that
your tags file gets updated periodically without any action on your part. I
recommend following the instructions outlined by Tim Pope on this matter,
which discusses a workflow coupled to git for managing the tags file. It
includes shell scripting that may not look "effortless"; however, the fact this
is automated helps to ensure unused is running against new versions of the
code as you (and other teammates, if you have any) are committing.

As he suggests, you'll want to run git init into the directories you want
this hook, and to manually run the hook:

git ctags

unused is configured to look for a tags file in three different directories,
including .git/ as the article suggests, so no further configuration will be
necessary with unused.

"Calculating cache fingerprint" takes a long time

unused attempts to be intelligent at understanding if your codebase has
changed before running analysis (since it can be time-consuming on large
codebases). To do so, it calculates a "fingerprint" of the entire directory by
using md5 (or md5sum), along with find and your .gitignore file.

If you're checking in artifacts (e.g. node_modules/, dist/, tmp/, or
similar), unused will likely take significantly longer to calculate the

Per the --help documentation, you can disable caching with the -C flag:

$ unused -C

"No results found" when expecting results

If you're expecting to see results but unused doesn't find anything, verify
that any artifacts unused uses (e.g. the tags file, wherever it's located)
or generates (e.g. in PROJECT_ROOT/tmp/unused) is .gitignored.

What might be happening is, because unused searches for tokens with ag
(which honors .gitignore), it's running into checked-in versions of the
tokens from other files, resulting in duplicate occurrences that aren't
representative of the actual codebase. The most obvious might be the tags
file itself, although if you're using an IDE that runs any sort of analysis
and that's getting checked in somehow, that may cause it too.

One final piece to check is the number of tokens in the tags file itself; if
ctags is misconfigured and only a handful of tokens are being analyzed, they
all may have low removal likelihood and not display in the default results
(high-likelihood only).

Analysis takes a long time due to a large number of terms found

In my experience, projects under 100,000LOC should have at most around 8,000
unique tokens found. This obviously depends on how you structure your
classes/modules/functions, but it'll likely be close.

If you're seeing more than 15,000 terms matched (I've seen upwards of 70,000),
this is very likely due to misconfiguration of ctags where it includes some
amount of build artifacts. In Ruby, this might be a RAILS_ROOT/vendor
directory, or if you're using NPM, APP_ROOT/node_modules or

When configuring ctags, be sure to include your --exclude directives; you
can find an example here.

Custom Configuration

The first time you use unused, you might see a handful of false positives.
unused will look in two additional locations in an attempt to load
additional custom configuration to help improve this.

Configuration format

# Language or framework name
#   e.g. Rails, Ruby, Go, Play
- name: Framework or language
  # Collection of matches allowed to have one occurrence
    # Low likelihood match name
    - name: ActiveModel::Serializer
      # Flag to capture only capitalized names
      #   e.g. would match `ApplicationController`, not `with_comments`
      classOrModule: true

      # Matcher for `.*Serializer$`
      #   e.g. `UserSerializer`, `ProjectSerializer`
      termEndsWith: Serializer

      # Matcher for `^with_.*`
      #   e.g. `with_comments`, `with_previous_payments`
      termStartsWith: with_

      # Matcher for `^ApplicationController$`
      termEquals: ApplicationController

      # Matcher for `.*_factory.ex`
      #   e.g. `lib/appname/user_factory.ex`, `lib/appname/project_factory.ex`
      pathEndsWith: _factory.ex

      # Matcher for `^app/policies.*`
      #   e.g. `app/policies/user_policy.rb`, `app/policies/project_policy.rb`
      pathStartsWith: app/policies

      # list of termEquals
      # Matcher allowing any exact match from a list
      - index?
      - edit?
      - create?


The first location is ~/.unused.yml. This should hold widely-used
configuration roughly applicable across projects. Here's an example of what
might be present:

- name: Rails
    - name: ActiveModel::Serializer
      termEndsWith: Serializer
      classOrModule: true
    - name: Pundit
      termEndsWith: Policy
      classOrModule: true
      pathEndsWith: .rb
    - name: Pundit Helpers
        - Scope
        - index?
        - new?
        - create?
        - show?
        - edit?
        - destroy?
        - resolve
    - name: JSONAPI::Resources
      termEndsWith: Resource
      classOrModule: true
      pathStartsWith: app/resources
    - name: JSONAPI::Resources Helpers
      - updatable_fields
      pathStartsWith: app/resources

I tend to work on different APIs, and the two libraries I most commonly use
have a fairly similar pattern when it comes to class naming. They both also
use that naming structure to identify serializers automatically, meaning they
very well may only be referenced once in the entire application (when they're
initially defined).

Similarly, with Pundit, an authorization library, naming conventions often
mean only one reference to the class name.

This is a file that might grow, but is focused on widely-used patterns across
codebases. You might even want to check it into your dotfiles.


The second location is APP_ROOT/.unused.yml. This is where any
project-specific settings might live. If you're working on a library before
extracting to a gem or package, you might have this configuration take that
into account.


unused will attempt to parse both of these files, if it finds them. If
either is invalid either due to missing or mistyped keys, an error will be


Unused leverages Ag to
analyze the codebase; as such, you'll need to have ag available in your
$PATH. This is set as an explicit dependency in Homebrew.

Alternatively, if you'd like to use
RipGrep, you can do so with the
--search rg flag. Be sure to have RipGrep installed first.


To run the test suite, run:

stack test


Copyright 2016-2017 Josh Clayton. See the LICENSE.

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