Merge pull request #2133 from marcosnils/feat/output_docs

docs: Add guide to showcase handling outputs
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Solomon Hykes 2022-04-13 13:46:07 -05:00 committed by GitHub
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---
slug: /1227/contributing
displayed_sidebar: europa
displayed_sidebar: 0.2
---
# Contributing to Dagger

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---
slug: /1226/handling-outputs
displayed_sidebar: 0.2
---
# Handling action outputs
It's most likely that upon executing a Dagger action, you'll find in the situation of having to parse some outputs. In Dagger 0.1 (pre-Europa), inputs and outputs had to be specifically defined; starting Dagger 0.2 (Europa) we introduced a brand new API which removed this capability temporarily until we come up with the [right UX](https://github.com/dagger/dagger/issues/1351) to bring this back. Until the API is ready, you can follow this guide which shows different **temporary** alternatives of parsing dagger outputs.
## Writing outputs to the filesystem
As showcased in the [interacting with the client](/1203/client) docs, Dagger already has the ability to write into the client filesystem through the `client` API. Using this capability we can then output any value into our local filesystem for further automation.
Here's a simple example of a plain text output:
```cue file=../tests/core-concepts/client/plans/output_simple.cue.fragment
```
After performing `dagger do test`, a new file named `output.txt` will be present in the current working directory with the output of the `bash.#Run` action.
## Marshalling multiple outputs
The above example works well for simple outputs, but most of the time some actions like [Netlify's](https://github.com/dagger/dagger/blob/main/pkg/universe.dagger.io/netlify/netlify.cue) can output mutiple values. In this case, Netlify's action is returning the deployment `url`, `deployUrl` and `logsUrl`. On this case, we can leverage on CUE's [default integrations](https://cuelang.org/docs/integrations/) and marshal all the values into a single `json` or `yaml` file.
Here's an example on how to marshal multiple output values:
```cue file=../tests/core-concepts/client/plans/output_marshal.cue.fragment
```

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#SomeAction: {
// Nop to make dagger run the action
core.#Nop & {}
url: "test.com"
deployUrl: "test.com/deploy"
logsUrl: "test.com/logs"
}
dagger.#Plan & {
client: filesystem: "output.json": write: contents: json.Marshal({
url: actions.test.url
deployUrl: actions.test.deployUrl
logsUrl: actions.test.logsUrl
})
actions: {
test: #SomeAction & {}
}
}

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dagger.#Plan & {
client: filesystem: "output.txt": write: contents: actions.test.export.files["/hello.txt"]
actions: {
_image: alpine.#Build & {
packages: bash: {}
}
test: bash.#Run & {
input: _image.output
script: contents: "echo Hello World! > /hello.txt"
export: files: "/hello.txt": string
}
}
}

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@ -53,6 +53,8 @@ module.exports = {
"guides/custom-buildkit",
"guides/self-signed-certificates",
"guides/pushing-plan-dependencies",
"guides/coding-style",
"guides/handling-outputs",
],
},
{