Part 4: Args

To copy the files for this example ( Part 4 ) run

earthly --artifact github.com/earthly/earthly/examples/tutorial/go:main+part4/part4 ./part4

Examples in Python, JavaScript and Java are at the bottom of this page.

Just Like Docker...Mostly

ARGs in Earthly work similar to ARGs in Dockerfiles, however there are a few differences when it comes to scope. Also, Earthly has a number of built in ARGs that are available to use.

Let's say we wanted to have the option to pass in a tag for our Docker image when we run earthly +docker.

docker:
    ARG tag='latest'
    COPY +build/example .
    ENTRYPOINT ["/go-workdir/example"]
    SAVE IMAGE go-example:$tag

In our +docker target we can create an ARG called tag. In this case, we give it a default value of latest. If we do not provide a default value the default will be an empty string.

Then, down in our SAVE IMAGE command, we are able to reference the ARG with $ followed by the ARG name.

Now we can take advantage of this when we run Earthly.

earthly +docker --tag='my-new-image-tag'

In this case my-new-image-tag will override the default value and become the new tag for our docker image. If we hadn't passed in a value for tag, then the default latest would have been used.

earthly +docker
# tag for image will be 'latest'

Passing ARGs in FROM, BUILD, and COPY

We can also pass ARGs when referencing a target inside an Earthfile. Using the FROM and BUILD commands, this looks pretty similar to what we did above on the command line.

docker:
    ARG tag='latest'
    COPY +build/example .
    ENTRYPOINT ["/go-workdir/example"]
    SAVE IMAGE go-example:$tag

with-build:
    BUILD +docker --tag='my-new-image-tag'

with-from:
    FROM +docker --tag='my-new-image-tag'

We can also pass ARGs when using the COPY command, though the syntax is a little different.

build:
    ARG version
    COPY main.go .
    RUN go build -o output/example-$version main.go
    SAVE ARTIFACT output/example-$version AS LOCAL local-output/go-example

with-copy:
    COPY (+build/example --version='1.0') .

Builtin ARGs

There are a number of builtin ARGs that Earthly offers. You can read about a complete list of them, but for now, let's take a look at how they work.

In order to use Earthly builtin ARGs they need to be pre-declared. Once you do that, you can use them just like any other ARG.

ARG USERARCH
RUN echo $USERARCH

In this case we've declared the ARG USERARCH which is a builtin that holds the processor architecture the target is being built from.

More Examples

JavaScript

To copy the files for this example ( Part 4 ) run

earthly --artifact github.com/earthly/earthly/examples/tutorial/js:main+part4/part4 ./part4

./Earthfile

VERSION 0.8
FROM node:13.10.1-alpine3.11
WORKDIR /js-example

deps:
    COPY package.json ./
    COPY package-lock.json ./
    RUN npm install
    # Output these back in case npm install changes them.
    SAVE ARTIFACT package.json AS LOCAL ./package.json
    SAVE ARTIFACT package-lock.json AS LOCAL ./package-lock.json

build:
    FROM +deps
    COPY src src
    RUN mkdir -p ./dist && cp ./src/index.html ./dist/
    RUN npx webpack
    SAVE ARTIFACT dist /dist AS LOCAL dist

docker:
    FROM +deps
    ARG tag='latest'
    COPY +build/dist ./dist
    EXPOSE 8080
    ENTRYPOINT ["/js-example/node_modules/http-server/bin/http-server", "./dist"]
    SAVE IMAGE js-example:$tag

Java

To copy the files for this example ( Part 4 ) run

earthly --artifact github.com/earthly/earthly/examples/tutorial/java:main+part4/part4 ./part4

./Earthfile

VERSION 0.8
FROM openjdk:8-jdk-alpine
RUN apk add --update --no-cache gradle
WORKDIR /java-example

deps:
    COPY build.gradle ./
    RUN gradle build

build:
    FROM +deps
    COPY src src
    RUN gradle build
    RUN gradle install
    SAVE ARTIFACT build/install/java-example/bin AS LOCAL build/bin
    SAVE ARTIFACT build/install/java-example/lib AS LOCAL build/lib

docker:
    COPY +build/bin bin
    COPY +build/lib lib
    ARG tag='latest'
    ENTRYPOINT ["/java-example/bin/java-example"]
    SAVE IMAGE java-example:$tag

Python

To copy the files for this example ( Part 4 ) run

earthly --artifact github.com/earthly/earthly/examples/tutorial/python:main+part4/part4 ./part4

./Earthfile

VERSION 0.8
FROM python:3
WORKDIR /code

deps:
    RUN pip install wheel
    COPY requirements.txt ./
    RUN pip wheel -r requirements.txt --wheel-dir=wheels
    SAVE ARTIFACT wheels /wheels

build:
    FROM +deps
    COPY src src
    SAVE ARTIFACT src /src

docker:
    COPY +deps/wheels wheels
    COPY +build/src src
    COPY requirements.txt ./
    ARG tag='latest'
    RUN pip install --no-index --find-links=wheels -r requirements.txt
    ENTRYPOINT ["python3", "./src/hello.py"]
    SAVE IMAGE python-example:$tag