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Minor edits to Environment variables section

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* Clarify the list of supported instructions.
* Clarify behavior of ONBUILD, based on comments by @SvenDowideit, @theJeztah in PR #14735.
* Reorder list of instructions in alphabetical order.

Signed-off-by: Charles Chan <charleswhchan@users.noreply.github.com>
Upstream-commit: 42263dafcf05dc598fd98d1b9dd098acb09a4e72
Component: engine
This commit is contained in:
Charles Chan
2015-07-18 21:09:48 -07:00
parent 2138eae5bf
commit d726a9a751
1 changed files with 12 additions and 6 deletions
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18
components/engine/docs/reference/builder.md
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@ -152,18 +152,24 @@ Example (parsed representation is displayed after the `#`):
ADD . $foo # ADD . /bar
COPY \$foo /quux # COPY $foo /quux
The instructions that handle environment variables in the `Dockerfile` are:
Environment variables are supported by the following list of instructions in
the `Dockerfile`:
* `ENV`
* `ADD`
* `COPY`
* `WORKDIR`
* `ENV`
* `EXPOSE`
* `VOLUME`
* `USER`
* `WORKDIR`
* `VOLUME`
`ONBUILD` instructions are **NOT** supported for environment replacement, even
the instructions above.
as well as:
* `ONBUILD` (when combined with one of the supported instructions above)
> **Note**:
> prior to 1.4, `ONBUILD` instructions did **NOT** support environment
> variable, even when combined with any of the instructions listed above.
Environment variable substitution will use the same value for each variable
throughout the entire command. In other words, in this example: