The Language Agnostic, All-Purpose, Incredible, Makefile

I like to use Makefiles. I like to use Makefiles in Java. I like to use Makefiles in Erlang. I like to use Makefiles in Elixir. And most recently, I like to use Makefiles in Ruby. I think you, too, would like to use Makefiles in your environment, and the engineering community would benefit if more of us used Makefiles, in general.

Make was born in 1976, making it one of the oldest tools in a programmer’s toolkit. Any tool that has been around this long is bound to have a mythology, stories, and examples that would be intimidating to someone unfamiliar with it. Additionally, I think many of us have written it off as no longer relevant, as we are not writing C programs, after all. Allow me to show you why it should not be intimidating, and furthermore, is applicable to your everyday workflow as an engineer.

Indicators that you may benefit from a Makefile

There are a number of indicators that a Makefile would do you good. These indicators are common enough that I’m sure some apply to you.

1. You have aliases or functions in your .bashrc that are specific to a project, such as

   alias chrome_rspec="CAPYBARA_JAVASCRIPT_DRIVER=chrome bundle exec bin/rspec"
    alias serve="bundle exec foreman start -f Procfile.dev

2. You use a disparate set of commands in a project, in particular those that use many different tools, a complex set of arguments, or environment variables, such as

   RAILS_ENV=test bundle exec rails db:migrate 
    rake db:seed
    bundle exec jekyll serve --drafts --incremental
    bundle exec rspec spec/features/*.rb
    bundle exec rails c

3. You keep notes in Evernote, an org file, or a text file to write down commonly used commands for a project.

4. You have to run certain commands before others. For example, when switching branches in a rails project, you might have to do something like

   bundle && RAILS_ENV=test bundle exec rails db:migrate \\
    && bundle exec rspec spec/features/

Benefits of a Makefile

1. Commands are local to the project they are used for (as opposed to your .bashrc)
2. Commands are stored in the project, so improvements are mutually shared.
3. Commands are version controlled with your project.
4. A Makefile is a list of useful commands within the domain of the project. All you have to do is look at it to get an idea of what you can do with a project. It is the entry point to the project.
5. The Makefile gives you an explicit dependency tree.
6. If there is a missing command, you can just add it! Your team will benefit from it.

Teams that don’t currently use Makefiles

These days, it isn’t surprising to join a startup that does not use Makefiles. Often, developers in these situations are using the tools that come with the software environment they are using. If its rails, they are going to be using bundle , rails , and rspec commands. With a Makefile, you will still be using these commands, but the Makefile will act as a wrapper around commands.

Use it for yourself even if they don’t want it

Because a Makefile is simply an abstraction over commonly used tools, there is no downside to using a Makefile even if your team doesn’t yet see the value in it; they can continue using their workflow while you use the Makefile. I would suggest committing it into the repository once you have developed a useful Makefile, and then when someone asks how to reseed a database, for example, you can mention “Just run make db-seed”.

What is a Makefile?

There are years of use cases and idiomatic practices that can make learning about Makefiles daunting. I want to introduce the basics so you can start using Makefiles right away. It turns out that Makefiles are very simple when we break them down.

The Makefile is a file, usually in the root of a project, with the name Makefile.

A Makefile is made up of rules . A rule contains a target , prerequisites , and commands which form a recipe .

target_1: prerequisite_1 ... prerequisite_n
    command_1
    ...
    command_n

Target

The target is the thing you want to do (run a test, build code, drop a database, etc).

Prerequisite

Prerequisites are the rules needed to run before the recipe can run. For example, imagine checking out a new ruby project and executing bundle exec rspec ; you will probably encounter an error about needing to run bundle first! So, running bundle is a prerequisite of running rspec tests.

If you are thinking “oh, but I don’t want to run bundle every time, don’t worry. Make can determine if a prerequisite needs to be run or not. We’ll get to that.

Command

A command is simply run in the shell ( sh by default). If your target is test , the command might be bundle exec rspec .

A dead simple example

file_1: 
    touch file_1

• The target is file_1 .
• There are no prerequisites.
• The command touch file_1 produces file_1 .

In a Makefile, it would be executed with make file_1 .

A dead simple walkthrough

Let’s add another target to the dead simple example.

file_2: file_1
    touch file_2

file_2
file_1
touch file_2

At this point, I strongly recommend you follow along with your own makefile. You will learn by doing. Create a makefile so that it looks like this:

file_1:
    touch file_1

file_2:
    touch file_2

And be sure to use tabs to indent the commands . This is a requirement that trips up every person new to Make. If you do not use tabs, you will receive an error that looks like this Makefile:5: *** missing separator. Stop.

Now, if we run make file_2 , it will first check for the target file_1 , and if that target does not exist, it will run the command to fulfill file_1 .

$ make file_2
touch file_1
touch file_2

If we subsequently run make file_2 , we will see a message like this make: 'file_2' is up to date. Make is telling us it doesn’t have to do anything because file_2 already exists.

$ make file_2
make: `file_2' is up to date.

Let’s rm file_2 , and then we see that make file_2 will touch file_2 but it will not touch file_1 .

$ rm file_2
$ make file_2
touch file_2

Can you predict what happens if we make file_2 at this point? If you are thinking it will say up to date again, you are getting it!

$ make file_2
make: `file_2' is up to date.

Okay, so what will happen if we touch file_1 and subsequently make file_2 ?

$ make file_2
touch file_2

Let’s explore what is going on here.

Okay, quick tangent here. When we touch a file, what happens? If the file doesn’t exist, it creates that file; but what if that file already exists?

$ ls -ahl file_1
-rw-r--r--  1 ben.brodie  staff     0B Aug  9 06:48 file_1
$ touch file_1
$ ls -ahl file_1
-rw-r--r--  1 ben.brodie  staff     0B Aug  9 06:50 file_1

Do you spot the difference? It updates the timestamp . Let’s look at this again.

$ ls -ahl
-rw-r--r--   1 ben.brodie  staff     0B Aug  9 06:50 file_1
-rw-r--r--   1 ben.brodie  staff     0B Aug  9 07:10 file_2
$ make file_2
make: `file_2' is up to date.
$ touch file_1
$ ls -ahl
-rw-r--r--   1 ben.brodie  staff     0B Aug  9 07:13 file_1
-rw-r--r--   1 ben.brodie  staff     0B Aug  9 07:10 file_2
$ make file_2
touch file_2
$ ls -ahl
-rw-r--r--   1 ben.brodie  staff     0B Aug  9 07:13 file_1
-rw-r--r--   1 ben.brodie  staff     0B Aug  9 07:13 file_2
$ make file_2
make: `file_2' is up to date.

Do you see what’s happening here? If the timestamp of the prerequisite is more recent than the timestamp of the current target, then the command for the current target will run. This is how Make determines if the command of a target should be run.

I Can’t Get No Preqrequisite Satisfaction

We have looked into the some of the mechanics of the Make operations, and the syntax of the Makefile, but how does this all work together, and what is the point of all this anyways? If it hasn’t clicked yet, that’s okay ; we are going to get there, I promise.

It will be helpful for a moment to think of a Makefile target as a tree, where each node represents a target, and an branch represents a target’s relationship to its prerequisites.

file_3 -- file_1
       \- file_2

Here we have three targets: file_1 , file_2 , and file_3 . file_3 has prerequisites file_2 and file_1 , and since these are both leaves, they do not have other prerequisites.

Represented in a makefile, it could look like this:

file_1: 
    touch file_1
  
file_2: 
    touch file_2
    
file_3: file_1 file_2
    touch file_3

So, we are thinking of a target in the Makefile as representing a tree of targets, where the target is the root, and the children of a node are the prerequisites of that node. If the prerequisite of a node isn’t satisfied (we’ll get into what that means exactly), make will travel the graph until it finds a node that is satisfied. Once it finds that satisfied prerequisite, it will reverse the path it just took to get to the satisfied prerequisite, and for each node in this path, it will execute the target (which itself could have its own other prerequisites).

Let’s look at a slightly more complex tree.

file_6 -- file_5 -- file_4
                 \- file_3 -- file_2
                           \- file_1

which corresponds to the following Makefile

file_1:
    touch file_1
    
file_2: 
    touch file_2
    
file_3: file_2 file_1
    touch file_3
    
file_4:
    touch file_4
    
file_5: file_4 file_3
    touch file_5
    
file_6: file_5
    touch file_6

Let’s say the output of your ls -ahl is the following:

-rw-r--r--   1 ben.brodie  staff     0B Aug  9 10:52 file_1
-rw-r--r--   1 ben.brodie  staff     0B Aug  9 10:52 file_2
-rw-r--r--   1 ben.brodie  staff     0B Aug  9 10:52 file_3

And we run

make file_6

make now will traverse the tree, pushing each child onto a stack recursively. Then, it will pop each node off the stack and check if it is satisfied. If it is not satisfied, it will run the command for that node.

stack.push(file_6) -> |file_6|
stack.push(file_5) -> |file_5, file_6|
stack.push(file_4) -> |file_4, file_5, file_6|
stack.push(file_3) -> |file_3, file_4, file_5, file_6|
stack.push(file_2) -> |file_2, file_3, file_4, file_5, file_6|
stack.push(file_1) -> |file_1, file_2, file_3, file_4, file_5, file_6|

stack.pop() -> file_1 <- |file_2, file_3, file_4, file_5, file_6|

Is file_1 satisfied? It is a leaf and it exists, so Yes .

stack.pop() -> file_2 <- |file_3, file_4, file_5, file_6|

Is file_2 satisfied? It is a leaf and it exists, so Yes .

stack.pop() -> file_3 <- |file_4, file_5, file_6|

Is file_3 satisfied? file_3 exists. It’s children are file_2 and file_3 , and their timestamps are older than the timestamp of file_3 , so Yes .

stack.pop() -> file_4 <- |file_5, file_6|

Is file_4 satisfied? It does not exist so No . Run the command.

touch file_4

stack.pop() -> file_5 <- |file_6|

Is file_5 satisfied? It does not exist so No . Run the command.

touch file_5

stack.pop -> file_6 <- | |

Is file_6 satisfied? It does not exist so No . Run the command.

touch file_6

We haven’t come up with a formal definition of satisfaction , but now we can. We know that for a target to be satisfied it must (1) exist and (2) the target’s timestamp must be newer than the timestamp of it’s prerequisites. We also know from this exercise that the entire tree is traversed, if any prerequisite in the tree is not satisfied, then the target of that prerequisite is also not satisfied . Therefore, (3) the prerequisite targets must be satisfied.

Satisfaction Summary

This section is just a summary of what we just arrived at. The properties of satisfaction for a target.

1. The target must exist.
2. The target’s timestamp must be newer than the timestamp of the target’s prerequisites.
3. The prerequisite targets must be satisfied.

Make is about files

So far, we have been talking about files. The first property requires that the “target exists” - a target’s existence is determined by a file of the same name existing. The timestamp requirement, that a timestamp must be newer than the timestamp of the prerequisites, is also only meaningful when the target name has a one-to-one correspondence with files.

This is the point at which one realizes what make is all about, and without some further prodding, it is easy to mistakenly believe that it may not be relevant to your set of problems or your language tools - but this is the naive fog of mis-perceptions clouding judgment - we will get to the good stuff soon enough.

Make is about files. Files are the primitives of how make operates, because files allow us to keep track of state . If the prerequisite of a target is satisfied, make won’t run the prerequisites . If some prerequisites along the line are satisfied, make will only run the prerequisites that are not satisfied .

This all comes down to that timestamp property - the target’s timestamp must be newer than the timestamp of the target’s prerequisites . Keep in mind that the third property makes this recursive, so it applies all the way down the tree of prerequisites.

Let’s consider the implications of the timestamp property. If a prerequisite’s timestamp is newer than the target’s timestamp, that means that the prerequisite was generated some time after the time the target was generated. A prerequisite relationship exists because something about the target depends on something about the prerequisite, therefore, if the prerequisite is newer, then we must have to regenerate the target, otherwise the target as it currently exists is outdated.

Time for an analogy. I’m booking a trip to Poland, and then flying to Tromsø, Norway by way of a flight from Riga, Latvia. I have to plan the return flight from Tromsø to Los Angeles, and the date at which I book that is dependent upon the date at which I am flying into Norway from Riga. Every time I update the date to fly to Tromso from Riga, I have to update the time I want to fly back to Los Angeles from Tromso, otherwise I could be left with half a day in Tromsø, or even end up with something impossible, like flying back to Los Angeles from Tromsø before landing in Tromsø.

Let’s formulate this as a Makefile, where we have four trip legs we need to coordinate.

1. Flight from Los Angeles to Kraków, Poland
2. Drive from Krakáw, Poland to Riga
3. Fly from Riga to Tromsø

4. Fly from Tromsø to Los Angeles

   schedule_flight_to_krakow: 
        echo $(krakow_date) > schedule_flight_to_krakow
   
    schedule_drive_to_riga: schedule_flight_to_krakow
        echo $(riga_date) > schedule_drive_to_riga
   
    schedule_flight_to_tromso: schedule_drive_to_riga
        echo $(tromso_date) > schedule_flight_to_tromso
   
    schedule_flight_to_los_angeles: schedule_flight_to_tromso
        echo $(los_angeles_date) > schedule_flight_to_los_angeles

Here I have introduced a new piece of syntax in make files - arguments. A word surrounded with a $(...) will be replaced by the string specified on the command line for that argument. For example, $(arg_1) will be replaced by file_1 in either of these invocations of make : arg_1=file_1 make file or make file arg_1=file_1 . Simple, right? Yes, it is.

So, to schedule the flight to Krakáw, we invoke make as make schedule_flight_to_krakow krakow_date=08/01/2019

Let’s see what it produced.

$ cat schedule_flight_to_krakow
10/01/2019

It would be easier to simply pass all of the dates and have make take care of creating all of the files. By default, make will run the first target in the file, and idiomatically we will call this target all .

all: schedule_flight_to_los_angeles

Now we can invoke this with or without all

$ make krakow_date=10/01/2019 \
       riga_date=10/15/2019 \
       tromso_date=10/20/2019 \
       los_angeles_date=10/23/2019
  echo 10/01/2019 > schedule_flight_to_krakow
  echo 10/15/2019 > schedule_drive_to_riga
  echo 10/20/2019 > schedule_flight_to_tromso
  echo 10/23/2019 > schedule_flight_to_los_angeles

Error handling

Let’s add some error handling so that we know which flight dates are required when we run make.

We can use sh itself to handle errors, in this case missing arguments.

all: schedule_flight_to_los_angeles

schedule_flight_to_krakow:
    @if [ -z "$(krakow_date)" ]; then \
        echo "You must set krakow_date"; exit 1; fi
    echo $(krakow_date) > schedule_flight_to_krakow

schedule_drive_to_riga: schedule_flight_to_krakow
    @if [ -z "$(riga_date)" ]; then \
        echo "You must set riga_date"; exit 1; fi
    echo $(riga_date) > schedule_drive_to_riga

schedule_flight_to_tromso: schedule_drive_to_riga
    @if [ -z "$(tromso_date)" ]; then \
        echo "You must set tromso_date"; exit 1; fi
    echo $(tromso_date) > schedule_flight_to_tromso

schedule_flight_to_los_angeles: schedule_flight_to_tromso
    @if [ -z "$(los_angeles_date)" ]; then \
        echo "You must set los_angeles_date"; exit 1; fi
    echo $(los_angeles_date) > schedule_flight_to_los_angeles

The @ simply specifies that make will not echo the command, which for error checking would be just noise.

Now if we run from a clean state, make will inform us of any necessary arguments that are necessary, and fail. Here we have left out riga_date .

$ make krakow_date=10/01/2019 \
       tromso_date=10/20/2019 \
       los_angeles_date=10/23/2019
  echo 10/01/2019 > schedule_flight_to_krakow
  You must set riga_date
  make: *** [schedule_drive_to_riga] Error 1

Let’s set the riga_date .

$ make riga_date=10/15/2019 \
        tromso_date=10/20/2019 \
        los_angeles_date=10/23/2019
  echo 10/15/2019 > schedule_drive_to_riga
  echo 10/20/2019 > schedule_flight_to_tromso
  echo 10/23/2019 > schedule_flight_to_los_angeles

Say we now want to reschedule the flight to Riga, Tromsø, and Los Angeles - we won’t be able to since we have already schedule the flight to Krakow.

$ make riga_date=10/16/2019 \
       tromso_date=10/21/2019 \
       los_angeles_date=10/24/2019
  make: Nothing to be done for `all'.

Prerequisites

make won’t allow us to reschedule once we have scheduled something.

$ make schedule_drive_to_riga riga_date=10/16/2019 
make: `schedule_drive_to_riga' is up to date.

But, for now, we can manually rm the file.

$ rm schedule_drive_to_riga

And then schedule it.

$ make schedule_drive_to_riga riga_date=10/16/2019

Let’s try to reschedule the flight to Los Angeles in the same manner.

$ rm schedule_flight_to_los_angeles
$ make schedule_flight_to_los_angeles los_angeles_date=10/24/2019
  You must set tromso_date
  make: *** [schedule_flight_to_tromso] Error 1

Make detects that our schedule_flight_to_tromso prerequisite is not satisfied because the timestamp of schedule_flight_to_riga is newer than the timestamp of schedule_flight_to_tromso , therefore it also must be updated! So, let’s do that.

$ make schedule_flight_to_los_angeles tromso_date=10/22/2019 los_angeles_date=10/24/2019
  echo 10/22/2019 > schedule_flight_to_tromso
  echo 10/24/2019 > schedule_flight_to_los_angeles

Make is not about files

So far, we have seen that the targets of a Makefile truly represent files . But, this seems limiting. For example, what if we want to make a reschedule target?

Previously, we had to manually rm the file to reschedule it. A reschedule target should allow us to run something like make reschedule_flight_to_los_angeles los_angeles_date=10/24/2019 .

It turns out that we can do this. If we consider what it means to reschedule, it seems there is no circumstance where we want to block the reschedule (i.e., we are actively rescheduling, therefore we intend to schedule when the date is already set).

How about something as simple as this:

reschedule_flight_to_los_angeles: schedule_flight_to_los_angeles
    @if [ -z "$(los_angeles_date)" ]; then \
        echo "You must set los_angeles_date"; exit 1; fi
        echo $(los_angeles_date) > schedule_flight_to_los_angeles

This looks familiar, as it is the same recipe as schedule_flight_to_los_angeles . Yet, it behaves differently. We can run it as many times as we want, and it won’t complain.

$ make reschedule_flight_to_los_angeles los_angeles_date=10/25/2019
  echo 10/25/2019 > schedule_flight_to_los_angeles
$ test$ make reschedule_flight_to_los_angeles los_angeles_date=10/26/2019
  echo 10/26/2019 > schedule_flight_to_los_angeles
$ test$ make reschedule_flight_to_los_angeles los_angeles_date=10/27/2019
  echo 10/27/2019 > schedule_flight_to_los_angeles

The essential difference is that the file being produced is not the same name as the target. Because do not create a file with the same name as the target, from Make sees this target as never up to date .

Earlier we implemented the all target - this target is also independent of a cooresponding file.

But, what if some other process does result in a file name clashing with a target?

It is probably a good idea to add a clean task to start our schedule fresh, as if we had never scheduled anything.

clean:
    rm schedule*

This will remove all files that begin with “schedule” in their name, effectively forgetting that we had ever scheduled anything.

It is not inconceivable, however, that some other process might result in a file named clean , resulting in a confusing bug.

$ touch clean
$ make clean
  make: `clean' is up to date.

Make has a special target called .PHONY , and any prerequisits of this target are always determined to be out-of-date, and will be always be run.

.PHONY: clean

And now when we run clean, it does not check if the file exists.

$ touch clean
$ make clean
  rm schedule*
  rm: schedule*: No such file or directory
  make: *** [clean] Error 1

Notice, however, that this results in an error, because we have already cleaned out the “schedule” files. Ideally, this should not result in an error; we expect success upon removing the files or if the files are already moved, and, if we can prevent this from resulting in error, then the clean target has the useful property of idempotency .

We can tell make to ignore errors with a - prepended to the recipe.

clean:
    -rm schedule*

Now when we run clean , the error will be ignored.

$ make clean
rm schedule*
rm: schedule*: No such file or directory
make: [clean] Error 1 (ignored)

An ignored error will still report the error, but it will not halt the Make process.

Our final, albeit highly contrived, Makefile looks as follows:

.PHONY: all clean reschedule_flight_to_los_angeles

all: schedule_flight_to_los_angeles

schedule_flight_to_krakow:
    @if [ -z "$(krakow_date)" ]; then \
        echo "You must set krakow_date"; exit 1; fi
        echo $(krakow_date) > schedule_flight_to_krakow

schedule_drive_to_riga: schedule_flight_to_krakow
    @if [ -z "$(riga_date)" ]; then \
        echo "You must set riga_date"; exit 1; fi
        echo $(riga_date) > schedule_drive_to_riga

schedule_flight_to_tromso: schedule_drive_to_riga
    @if [ -z "$(tromso_date)" ]; then \
        echo "You must set tromso_date"; exit 1; fi
        echo $(tromso_date) > schedule_flight_to_tromso

schedule_flight_to_los_angeles: schedule_flight_to_tromso
    @if [ -z "$(los_angeles_date)" ]; then \
        echo "You must set los_angeles_date"; exit 1; fi
        echo $(los_angeles_date) > schedule_flight_to_los_angeles

reschedule_flight_to_los_angeles: schedule_flight_to_los_angeles
    @if [ -z "$(los_angeles_date)" ]; then \
        echo "You must set los_angeles_date"; exit 1; fi
        echo $(los_angeles_date) > schedule_flight_to_los_angeles

clean:
    -rm schedule*

Making it fit with Ruby (or any other language)

I’ve given an overview of Make, along with a contrived example. Now I would like to illustrate how this can be used as a practical tool in your development workflow.

I think that many developers feel that their build tool that comes with their language is all they need - just run rspec test , rails server , or npm install to get some task done.

However, many of these tools don’t make use of dependency relationships, and often what comes out of the box can’t know what those dependency relationships are. For example, I worked on a Rails project, where Javascript had to be compiled by Webpacker if there were any changes to the front-end layer. The integration tests in our test suite exercised the web front-end, and if Webpacker was not run when a change was introduced, tests could fail, leading to incorrect conclusions about the state of the code, and a lot of wasted time until the developer realized “Oh, I forgot to run Webpacker!”.

Additionally, if you were running the server live on your machine, there was a Webpacker process watching for live code changes and recompiling the Javascript when a change happened - so in this case, if the developer ran the integration tests, the tests would accurately reflect the current state of the code.

The success of the test suite should not rely on an assumption that another process is running and watching code. First, if that process is not running, then the tests can’t pass. Second, this implies that the prerequisites for that test suite are not captured in the test command, which can lead to issues on a CI server, a clean checkout of code, or a new developer setting up. A successful test suite should never rely on the state of externalities. This leads to inconsistent behavior.

I don’t suggest that its wrong to have a process watching code and recompiling, that is perfectly fine for the goal of having a self-updating live site for experimentation - but that is simply a different use case than running a test suite, so don’t mix them.

One could also simply have a script that runs all of the prerequisites before running a test, but that script wouldn’t have a system of keeping track of what needs to be run and what doesn’t. If the Javascript is already compiled, then it would waste time to wait for it to compile each time you run a test. Make determines if the Javascript needs to be compiled due to changes.

One could use Rake to capture the prerequisites for the test run. This would be a perfectly acceptable approach. However, there is likely a reason that I haven’t seen this done; Rake is complex, coupled to the project in ways that don’t generalize easily, and the tasks that come out of the box are written to exercise the framework (rails).

Rake, although named to suggest it is Ruby Make, is neither a replacement for make, nor does it conflict with make. Instead, I see Rake as being a useful tool for Ruby and Framework specific tasks, like database migrations, while Make fits in as the general purpose glue to connect all of these commands and dependencies. It is simpler to write a command in Make and declare it’s dependencies than doing so in Rake, and the Makefile can actually leverage the Rake tasks that already exist, by calling rake some_task in the recipe.

Furthermore, Make is language agnostic, so it fits nicely into any project. A developer can simply look at the Makefile in a given project, and they have list of commands that exercise that project, even if they are unfamiliar with the language or framework.

I want to reiterate that Make does not replace a given build tool, it simply wraps around those tools to make doing higher level things simpler and consistent.

An Actual Example

Even a simple project can benefit greatly from a Makefile. A few months ago, I was asked to put together a small project for interview test. This project involved a backend server, and a front-end component in React. As I ran various commands and patterns emerged, I added them to the Makefile. Because modern build tools sometimes have side effects that are not captured as a file, such as bundle exec rake db:setup , which sets up the database, I devised a pattern for the Makefile to capture that these tasks had occurred, so they would not run if not needed.

.PHONY: serve live-reload db-reset db-setup db-migrate init deps compile bundle yarn clean

serve: init deps compile db-setup db-migrate
    rails server

live-reload: yarn
    ./bin/webpack-dev-server --host 127.0.0.1

db-reset:
    bundle exec rake db:reset

db-setup: .make.db-setup

db-migrate: .make.db-migrate

init: .make.init

deps: bundle yarn

compile: .make.webpacker

bundle: .make.bundle

yarn: .make.yarn

clean:
    rm .make.*

.make.webpacker: $(shell find app/javascript -type f)
    ./bin/webpack
    touch .make.webpacker

.make.db-setup: .make.bundle
    bundle exec rake db:setup
    touch .make.db-setup

.make.db-migrate: .make.bundle $(shell find db/migrate -type f)
    bundle exec rails db:migrate
    touch .make.db-migrate

.make.bundle: Gemfile
    bundle
    touch .make.bundle

.make.yarn: package.json
    yarn
    touch .make.yarn

.make.init:
    gem install bundler
    touch .make.init

Take a minutes to look this over and understand it. Our main entry-point here, and what will run by default on an invocation of make without arguments, is serve .

init

Let’s go through the prerequisites of the serve target. First, there is an init prerequisite. This prerequisite ensures that bundler is installed (but could also be used for installing requirements with homebrew, for example). init has a prerequisite .make.init which first runs gem install bundler and then creates the file .make.init . Because .make.init is the name of the file it creates, it will never run again (unless the file is deleted). This is a simple way of capturing side effects as a file to indicate that the task has already been run.

deps

deps ensures that all dependencies have been installed to the project and if any new versions have been specified, or dependencies have been added or removed from the project, the dependencies will be updated. deps has two prerequisites - bundle and yarn .

bundle

bundle runs bundle to update the Ruby dependencies of the project if and only if the Gemfile file has been updated. We see this in the .make.bundle target which has a prerequisite of Gemfile , which is just that file. After bundle has successfully run, the file .make.bundle is created. Whenever the timestamp of Gemfile is newer than the timestamp of .make.bundle , which is precisely what would happen in the case of added, removing, and changing the version of a dependency, the task will be run again! Otherwise, it won’t do anything.

yarn

yarn does the same thing as the bundle target, except that this task is dependent on the package.json file, and runs the yarn command.

compile

compile runs webpack to compile the Javascript. Importantly, it only does this if any of the Javascript files have been updated. It does this by setting it’s prerequisites as all of the Javascript files! If any one of them has a timestamp newer than the .make.webpacker file, then it will run webpack . This target also introduces us to two new concepts in the makefile: the shell function, and dynamically generated prerequisites. As you can see, the ability to dynamically generate prerequisites is very powerful. The shell function simply runs the command in the shell, and returns what the function returns, in this case a list of all files in the app/javascript directory.

db-setup

db-setup runs bundle exec rake db:setup if it hasn’t been run yet. If bundle hasn’t been installed first, it will install it.

db-migrate

db-migrate is a really nifty target to have in a rails project. Before I figured this one out, quite often I would switch to another branch, or pull new code, and then my database would be out of sync with the migrations. This target automates this problem away. Never again will you see a message about needing to run migrations! Like compile , db-migrate uses the shell function to dynamically generate a list of prerequisites that are all migrations in the project. If any of them are newer than .make.db-migrate , it runs bundle exec rails db:migrate . If bundle has yet to be installed, it will install it first.

serve

Once all of those are done, it’s time to serve the application - rails server does the trick.

Adding a new target

There is something missing here… no test target! But, notice how simple it would be to add a test target. We already have all of the required target prerequisites defined. They are the same as those for the serve target.

test: init deps compile db-setup db-migrate
    rspec test

Developing a Makefile along with developing code is quite natural, and once a solid foundation is laid, it is often this simple to define new targets.

gitignore

Because this results in .make.* files, be sure to echo .make.* > .gitignore to avoid checking them into git.

Decoupled Freedom

Because Make is a general purpose tool that is decoupled from languages and frameworks, it becomes incredibly freeing once Make becomes part of the workflow.

For example, I am working on a project at the moment that requires a database to be loaded in order to run the server. I realized that it would be less coupled to my own system if I simply spun up a database with docker instead of relying on a database actually running as a service on my machine.

Often, using docker in a project can become problematic, because there is no out of the box tooling in place to manage the docker instances. Sometimes docker is running, and all goes well, sometimes it isn’t running, requiring the developer to remember one of those confusing docker commands (is it create, run, exec, or start?). What happens if the database on the docker image gets trashed? Now you need to remember another set of commands to reset the database.

Makefiles allow the developer to create a workflow with docker that isn’t confusing, and remains consistent and predictable.

Using a Makefile allows me to start mysql as a dependency when I run the server (or, when I need it for a test). I have modified it below as an example.

...
run: build mysql-start
    ./start-myapp

mysql-create: 
    @docker container ls -a | grep my_app_mysql || \
      (docker create -p 3306:3306 \
        --name my_app_mysql \
        -v $$(pwd)/mysql/docker-entrypoint-initdb.d:/docker-entrypoint-initdb.d \
        -v $$(pwd)/mysql/mysql-keyring:/var/lib/mysql-keyring \
        -e MYSQL_ROOT_PASSWORD=password \
        mysql:8.0.18 \
        --early-plugin-load=keyring_file.so \
        --lower-case-table-names=1

mysql-start: mysql-create
    docker start my_app_mysql
    while ! docker exec my_app_mysql -h 127.0.0.1 -ppassword -e \
    "\q" 2> /dev/null; do echo "Waiting for MySQL..." && sleep 1; done
    
mysql-stop:
    docker stop my_app_mysql
    
mysql-clean:
    docker rm my_app_mysql
    
mysql-shell:
    docker exec -it my_app_mysql -h 127.0.0.1 -ppassword
    
mysql-logs
    docker logs my_app_mysql
...

As you can see, our recipes can become quite complex once we have some requirements. Here, we have a schema that has encryption enabled, so it requires some configuration around that. Running these manually would be unproductive. mysql-create only creates the container if the container doesn’t already exist. I am using || to accomplish this. Furthermore, in mysql-start , docker start is idempotent, so if container is started, it will work just fine. The while loop checks that a process can connect to mysql , and if it cannot, it waits one second and attempts to check again. This is necessary as the mysql database process is not always available immediately, so we need to wait until it is up to connect to it.

Without a Makefile in place, we simply would not have the freedom to get docker into our development workflow in a consistent manner. At best, we would have some scripts for stopping and starting the container, but these would have to be run manually, inevitably leading to accidently running the server without the database up, and mysterious requirements that an on-boarding developer may not be aware of.

How to develop a Makefile

They key to successfully writing a Makefile is to just write down the commands you need at the moment. Ran a new command? Put it in the Makefile. Over time, the Makefile will grow to include even those rare commands you rarely run and can’t remember what they were. Patters with emerge, and these will help guide the prerequisites that may otherwise not be obvious.

It is essential to not attempt to define all of the commands up front. Updating and refining the Makefile is part of the development workflow itself; things change, and so does the Makefile over time. Because the Makefile is general and flexible, these changes are usually quite simple to implement. Additionally, because developers will be running makefiles all the time , they stay up to date, unlike documentation. If it doesn’t work, it will require an immediate fix.

Go for it

I hope that I have clarified Makefiles and perhaps convinced you of their power. Just go ahead and try it in your current project, and see what it can do for you.

Further Reading

1. Notes For New Make Users
2. The Official Manual