Improve docs about ARG in FROM #333
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| @@ -530,8 +530,10 @@ FROM extras:${CODE_VERSION} | |||
| CMD /code/run-extras | |||
| ``` | |||
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| To use the default value of an `ARG` declared before the first `FROM` use an | |||
| `ARG` instruction without a value: | |||
| An `ARG` declared before a `FROM` is outside of a build stage, so it | |||
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Maybe better to mention that every stage has individual args, then it is better to understand that "arg-in-from" is not an exception but just follows the rule.
How about this example:
ARG VERSION=latest
FROM busybox:$VERSION
ARG VERSION
RUN echo $VERSION > image_version
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Maybe something like "An ARG instructions is only relevant for the next FROM instruction that comes after it in the Dockerfile, and then using this example to illustrate that.
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Maybe something like "An ARG instructions is only relevant for the next FROM instruction that comes after it in the Dockerfile,
That's not exactly correct. There are two cases:
- any
ARGbefore the firstFROMcan be used in anyFROMline - any
ARGwithin a build stage (after aFROM) can be used in that build stage
I can add more details to the ARG reference section as well (this stuff is under FROM) , but I think this line needs to be updated as well something along the lines of what I have.
| @@ -530,8 +530,10 @@ FROM extras:${CODE_VERSION} | |||
| CMD /code/run-extras | |||
| ``` | |||
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| To use the default value of an `ARG` declared before the first `FROM` use an | |||
| `ARG` instruction without a value: | |||
| An `ARG` declared before a `FROM` is outside of a build stage, so it | |||
There was a problem hiding this comment.
Maybe something like "An ARG instructions is only relevant for the next FROM instruction that comes after it in the Dockerfile, and then using this example to illustrate that.
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I've updated to include more details, and added some more structure to the |
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The text lgtm but the examples could be better. The image_version example was specifically for the case where it may make sense to use the same variable in FROM and inside the stage. I would switch the examples and make "arg-in-from" use the image_version and arguments in multiple stages use ARG SETTINGS.
Signed-off-by: Daniel Nephin <dnephin@docker.com>
Signed-off-by: Daniel Nephin <dnephin@docker.com>
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Makes sense, I've swapped the examples. |
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LGTM |
See docker/for-linux#59 and moby/moby#31352 (comment) and moby/moby#34008