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
ARG
s in Earthly work similar to ARG
s in Dockerfiles, however there are a few differences when it comes to scope. Also, Earthly has a number of built in ARG
s 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 ARG
s 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:$tag
with-build:
BUILD +docker --tag='my-new-image-tag'
with-from:
FROM +docker --tag='my-new-image-tag'
We can also pass ARG
s when using the COPY
command, though the syntax is a little different.
build:
ARG version
COPY main.go .
RUN go build -o output/example-$version main.go
SAVE ARTIFACT output/example-$version AS LOCAL local-output/go-example
with-copy:
COPY (+build/example --version='1.0') .
Builtin ARG
s
ARG
sThere are a number of builtin ARG
s 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 ARG
s 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.
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