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Referral πŸ”

Referral is a CLI to help you undertake complex analyses and refactorings of Ruby codebases. It finds, filters, and sorts the definitions & references of most types of Ruby identifiers (e.g. classes, methods, and variables) throughout your code.

Think of referral as a toolkit for tracking down references in your code for any number of purposes, offering a boatload of command-line options to enable you to efficiently accomplish things like:

  • Size up a codebase by gathering basic statistics and spotting usage hotspots
  • Build a to-do list to help you manage a large or complex refactor
  • Quickly make a list of every call to a deprecated method, rather than wait for warnings at runtime
  • Get a sense for how many callers would be impacted if you were to delete a method
  • Before renaming a module, verify there aren't already any other modules with the new name
  • Verify that you removed every reference to a deleted class before you merge
  • Identify dead code, like method definitions that aren't invoked anywhere
  • Catch references that haven't been updated since a change that affected them (according to git-blame)

Because Referral is powered by the introspection made possible by Ruby 2.6's RubyVM::AbstractSyntaxTree API, it must be run with Ruby 2.6 or later. Nevertheless, it can often analyze code listings designed to run on older Rubies.


From the command line:

$ gem install referral

Or in your Gemfile

gem "referral", require: false, group: :development

How to use Referral

Basic usage

At its most basic, you can just run referral and it'll scan **/*.rb from the current working directory and print every reference it finds:

$ referral
app/channels/application_cable/channel.rb:1:0: module  ApplicationCable
app/channels/application_cable/channel.rb:2:2: class ApplicationCable Channel
app/channels/application_cable/channel.rb:2:18: constant ApplicationCable::Channel ActionCable::Channel::Base
# … and then another 2400 lines (which you can easily count with `referral | wc -l`)

By default, Referral will sort entries by file, line, and column. Default output is broken into 4 columns: location, type, scope, and name.

If you'd like to scan a subset of files, you can pass a final argument with file paths and directories. For example, if you only wanted to search code in the top-level of app/lib you could run referral app/lib/*.rb. Or, if you wanted to include subdirectories, referral app/lib.

Everything above can be custom-tailored to your purposes, so let's work through some example recipes to teach you Referral's various features below. (Or, feel free to skip to the full list of options).

Recipe: build a refactoring to-do spreadsheet

When I'm undergoing a large refactor, I like to start by grepping around for all the obvious definitions and references that might be affected. Suppose I'm going to make major changes to my User class. I might use Referral's --exact-name filter like this:

referral --exact-name User,user,@user,@current_user

[Fun fact: if I'd have wanted to match on partial names, I could have used the looser --name, or for fully-qualified names (e.g. API::User), the stricter --full-name option.]

Next, I usually find it easiest to work through a large refactor file-by-file, but in certain cases where I'm looking for a specific type of reference, it makes more sense to sort by the fully-qualified scope, which can be done with --sort scope:

referral --exact-name User,user,@user,@current_user --sort scope

The above will sort results by their fully-qualified names (e.g. A::B#c), rather than their filenames.

Of course, if we want a checklist, the default output could be made a lot nicer for export to a spreadsheet app like Numbers. Here's how you might invoke referral to save a tab-separated-values (TSV) file:

referral --exact-name User,user,@user,@current_user --sort scope --print-headers --delimiter "\t" > user_refs.tsv

Where --print-headers prints an initial row of the selected column names, and --delimiter "\t" separates each field by a tab (making it easier to ingest for a spreadsheet app like Excel or Numbers), before being redirected to the file user_refs.tsv.

Now, to open it in Numbers, I'd run:

open -a Numbers user_refs.tsv

And you'll be greeted by a spreadsheet. And hey, why not throw a checkbox column on there while you're at it:

Screen Shot 2019-06-27 at 1 27 42 PM

It is important to note that Numbers, like earlier versions of Excel, uses an unsigned Integer for row numbering that limits the number of shown rows to ~65,000. On larger codebases, referral may create more references than this. LibreOffice and newer versions of Excel do not have this limitation on viewing.

Recipe: detect references you forgot to update

When working in a large codebase, it can be really tough to figure out if you remembered to update every reference to a class or method across thousands of files, so Referral ships with the ability to get some basic information from git-blame, like this:

referral --column file,line,git_sha,git_author,git_commit_at,full_name

By setting --column to a comma-separated array that includes the above, Referral will print results that look like these:

test/lib/splits_furigana_test.rb 56 634edc04 2017-09-04T13:34:09Z SplitsFuriganaTest#test_nasty_edge_cases.assert_equal
test/lib/splits_furigana_test.rb 56 634edc04 2017-09-04T13:34:09Z h
test/lib/splits_furigana_test.rb 56 634edc04 2017-09-04T13:34:09Z

[Warning: running git-blame on each file is, of course, a bit slow. Running this command on the KameSame codebase took 3 seconds of wall-time, compared to 0.7 seconds by default.]

And it gets better! Since we're already running blame, why not sort every line by its most and least recent commit time? You can! To list the least-recently-changed references first, add the option --sort least_recent_commit:

referral --sort least_recent_commit --column file,line,git_sha,git_author,git_commit_at,full_name

In my case, I see that my least-recently-updated Ruby reference is:

app/channels/application_cable/channel.rb 1 2017-08-20T14:59:35Z ApplicationCable

The inclusion of git-blame fields and sorting can be a powerful tool to spot-check a large refactor before deciding to merge it in.

Recipe: search for a regex pattern and print the source

Once in a while, I'll want to scan line-by-line in a codebase for lines that match a given pattern, and in those cases, the --pattern option and source column can be a big help.

Suppose I'm trying to size up a codebase by looking for how many methods appear to have a lot of arguments. While definitely imperfect and regex cannot parse context-free grammars, I can get a rough gist by searching for any lines that have 4 or more commas on them:

referral --pattern "/^([^,]*,){4,}[^,]*$/" -c location,source

Which would yield results like this one:

app/lib/card.rb:22:2:   def self.from_everything(id:, lesson_type:, item:, assignment:, meaning:)

Naturally, other programs like find could do this just as well, but the added ability to see & sort by when these lines were last updated in git might be interesting. Additionally, suppose you only wanted to find method definitions with a lot of (apparent) arguments? You could filter the matches down with --type instance_method,class_method, too, like this:

referral --pattern "/^([^,]*,){4,}[^,]*$/" -c location,git_commit_at,source -s most_recent_commit --type instance_method,class_method

In my results, I learned that as recently as June 6th, I wrote a very long method definition:

app/lib/presents_review_result.rb:60:2: 2019-06-02T02:38:01Z   def item_result(study_card_identifier, user, answer, item, learning, judgment, reward)

find couldn't have told me that (I don't think)!

Recipe: Find calls that have more than 1 argument

Recently I was upgrading the i18n gem and came across some bugs introduced by this change. To fix the issue, I started looking at all the places I18n.t was called from:

referral --type call --exact-name I18n.t -c location,source

Unfortunately, this produces 250+ false positives because the predominant usage was to pass a single argument to t. Only calls with more than 1 argument are affected by this change. --pattern doesn't work very well in this codebase, because calls to t with multiple arguments are more likely to be multiline.

referral --type call --exact-name I18n.t --arity 2+ -c location,source,arity

This produced 27 results I could quickly skim through.


Referral provides a lot of options. The help output of referral --help will print out the available options and their defaults:

Usage: referral [options] files
    -v, --version                    Prints the version
    -h, --help                       Prints this help
    -n, --name [NAME]                Partial or complete name(s) to filter
        --exact-name [NAME]          Exact name(s) to filter
        --full-name [NAME]           Exact, fully-qualified name(s) to filter
        --scope [SCOPE]              Scope(s) in which to filter (e.g. Hastack#hide)
    -p, --pattern [PATTERN]          Regex pattern to filter
    -t, --type [TYPES]               Include only certain types. See Referral::TOKEN_TYPES.
        --arity [ARITY]              Number of arguments to a method call.  (e.g. 2+)
        --include-unnamed            Include reference without identifiers (default: false)
    -s, --sort {file,scope}          (default: file). See Referral::SORT_FUNCTIONS
        --print-headers              Print header names (default: false)
    -c, --columns [COL1,COL2,COL3]   (default: location,type,scope,name). See Referral::COLUMN_FUNCTIONS
    -d, --delimiter [DELIM]          String separating columns (default: ' ')

A few things to note:

  • Each of --name, --exact-name, --full-name, --scope, --type, and --columns accept comma-separated arrays (e.g. --name foo,bar,baz)

  • --arity accepts a number with an optional + or -.

    • --arity 0 Match calls with 0 arguments
    • --arity 1+ Match calls with 1 or more arguments
    • --arity 1- Match calls with 1 or fewer arguments
  • You can browse available sort functions in Referral::SORT_FUNCTIONS for use with --sort. Each key is the name to be specified on the command line. (If you're feeling adventurous, we've left the hash unfrozen so you can define your own custom sorts dynamically, but YMMV.)

  • Just like sort functions, you can find the available column types in Referral::COLUMN_FUNCTIONS when passing a comma-separated list to --column. (This hash has also been left mutable for you, dear user.)

  • The types of AST nodes that Referral supports can be found in Referral::TOKEN_TYPES when filtering to certain definition & reference types with --type

  • Note that the columns git_sha, git_author, git_commit_at and the sort functions most_recent_commit and least_recent_commit will slow things down a bit, by invoking git-blame for each file included in the filtered results

  • The source column and --pattern options will read each file in the result set twice: once when parsing the AST, and again when printing results

Running with Ruby version managers

Referral requires Ruby version >= 2.6, but your codebase may be running on something older. You have a few options for using referral. You could 1) change your project's ruby while you run referral and then change it back, but this seems cumbersome and likely to cause annoyance. There are better ways.

Run from outside your project's working directory

If you cd .. from your project's working directory (assuming in that context you are running Ruby 2.6.x), you can run referral commands on your codebase by passing the path to that codebase to referral:

$ referral MyAwesomeProject/

This works for many of referrals features, but isn't ideal when it comes to git; columns like git_sha, git_author or git_commit_at will show empty results.

Running with rbenv

If you're using rbenv, you could temporarily switch your project's ruby to 2.6.x, but you'd have to remember to switch it back again before running any of the code in the project. To instantaneously switch to 2.6 and then back again (after the referral command finishes), do this (from your MyAwsomeProject directory):

$ RBENV_VERSION=2.6.3 referral

Running with RVM

The corresponding way to do this with rvm would be:

$ rvm 2.6.3 do referral

Code of Conduct

This project follows Test Double's code of conduct for all community interactions, including (but not limited to) one-on-one communications, public posts/comments, code reviews, pull requests, and GitHub issues. If violations occur, Test Double will take any action they deem appropriate for the infraction, up to and including blocking a user from the organization's repositories.


πŸ•΅οΈβ€β™€οΈ Find, filter, and sort your Ruby code's definitions & references




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