Is it possible to split the build_args across multiple lines?

[wilmardo]

For some build I use a delimited string as input to loop over and do some action on in the Dockerfile. For example:
https://github.com/LANsible/docker-home-assistant/blob/main/.github/workflows/docker.yml#L19
https://github.com/LANsible/docker-home-assistant/blob/main/Dockerfile#L49

This now becomes one line, it would be nice to be able to split this across multiple lines, anyone an idea?
Something like this?

      build_args: |
        COMPONENTS=mqtt|buienradar|denonavr|androidtv|opentherm_gw|utility_meter|season|unifi|home_connect|stookwijzer
        CUSTOM_COMPONENTS=
           https://github.com/golles/ha-knmi/archive/refs/tags/v3.0.4.tar.gz|
           https://github.com/danielrivard/homeassistant-innova/archive/refs/tags/v1.5.1.tar.gz|
           https://github.com/marcolivierarsenault/moonraker-home-assistant/archive/refs/tags/1.11.1.tar.gz|
           https://github.com/kamaradclimber/heishamon-homeassistant/archive/refs/tags/1.18.3.tar.gz|
           https://github.com/mampfes/hacs_waste_collection_schedule/archive/refs/tags/2.10.0.tar.gz|
           # would be cool if comments in between are possible as well, to setup renovate
           https://github.com/PhantomPhoton/S3-Compatible/archive/refs/tags/v1.0.2.tar.gz

I tried a couple different things but couldn't get it to work, anyone some input? If refactoring the build-args is required that is fine by me as well, I am open for suggestion.

Thanks all <3

[ideacatlab]

Two ways, depending on whether you mind the newlines ending up in the value.

The action splits the input on newlines, but it parses it with a CSV parser, and a double-quoted field is allowed to span lines. So quoting the whole KEY=value keeps it as one build arg:

build-args: |
  COMPONENTS=mqtt|buienradar|denonavr
  "CUSTOM_COMPONENTS=https://github.com/golles/ha-knmi/archive/refs/tags/v3.0.4.tar.gz|
  https://github.com/danielrivard/homeassistant-innova/archive/refs/tags/v1.5.1.tar.gz"

That does give you a single CUSTOM_COMPONENTS, but the line breaks survive inside the value, so you'd have to strip them in the Dockerfile before splitting on |.

If you want it readable in the workflow and clean when it arrives, fold it in YAML instead. In a double-quoted scalar a trailing backslash eats the newline completely — no space, no \n:

env:
  CUSTOM_COMPONENTS: "https://github.com/golles/ha-knmi/archive/refs/tags/v3.0.4.tar.gz|\
    https://github.com/danielrivard/homeassistant-innova/archive/refs/tags/v1.5.1.tar.gz|\
    https://github.com/marcolivierarsenault/moonraker-home-assistant/archive/refs/tags/v1.2.0.tar.gz"

jobs:
  build:
    steps:
      - uses: docker/build-push-action@v6
        with:
          build-args: |
            COMPONENTS=mqtt|buienradar|denonavr
            CUSTOM_COMPONENTS=${{ env.CUSTOM_COMPONENTS }}

The arg reaches the Dockerfile as one unbroken a|b|c string, and your existing loop keeps working unchanged. Note it's >- that people usually reach for first, but that joins the lines with spaces, which you don't want with a | delimiter.