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Distinguish ENV from setting environment inline

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It's ambiguous to say that `ENV` is _functionally equivalent to prefixing the command with `<key>=<value>`_. `ENV` sets the environment for all future commands, but `RUN` can take chained commands like `RUN foo=bar bash -c 'echo $foo' && bash -c 'echo $foo $bar'`. Users with a solid understanding of `exec` may grok this without confusion, but less experienced users may need this distinction.

Signed-off-by: Michael A. Smith <msmith3@ebay.com>

Improve Environment Handling Descriptions

- Link `ENV` and `Environment Replacement`
- Improve side-effects of `ENV` text
- Rearrange avoiding side effects text

Signed-off-by: Michael A. Smith <msmith3@ebay.com>
This commit is contained in:
Michael A. Smith 2015-01-22 10:09:50 -05:00 committed by Michael A. Smith
parent 0d5a1cbaae
commit 9f6e7e9aed
1 changed files with 7 additions and 7 deletions
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14
docs/sources/reference/builder.md
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@ -113,7 +113,7 @@ was no formal definition on as to which instructions handled environment
replacement at the time. After 1.3 this behavior will be preserved and
canonical.
Environment variables (declared with the `ENV` statement) can also be used in
Environment variables (declared with [the `ENV` statement](#env)) can also be used in
certain instructions as variables to be interpreted by the `Dockerfile`. Escapes
are also handled for including variable-like syntax into a statement literally.
@ -349,9 +349,8 @@ accessible from the host by default. To expose ports to the host, at runtime,
ENV <key>=<value> ...
The `ENV` instruction sets the environment variable `<key>` to the value
`<value>`. This value will be passed to all future
`RUN`, `ENTRYPOINT`, and `CMD` instructions. This is
functionally equivalent to prefixing the command with `<key>=<value>`
`<value>`. This value will be in the environment of all "descendent" `Dockerfile`
commands and can be [replaced inline](#environment-replacement) in many as well.
The `ENV` instruction has two forms. The first form, `ENV <key> <value>`,
will set a single variable to a value. The entire string after the first
@ -382,9 +381,10 @@ from the resulting image. You can view the values using `docker inspect`, and
change them using `docker run --env <key>=<value>`.
> **Note**:
> One example where this can cause unexpected consequences, is setting
> `ENV DEBIAN_FRONTEND noninteractive`. Which will persist when the container
> is run interactively; for example: `docker run -t -i image bash`
> Environment persistence can cause unexpected effects. For example,
> setting `ENV DEBIAN_FRONTEND noninteractive` may confuse apt-get
> users on a Debian-based image. To set a value for a single command, use
> `RUN <key>=<value> <command>`.
## ADD