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build.md: Document --build-arg without value 

This use case is currently _working correctly_, which is nice, but there is no documentation to be found about it. This PR fixes that.

Signed-off-by: Per Lundberg <perlun@gmail.com>
This commit is contained in:
Per Lundberg 2018-04-12 11:58:13 +03:00
parent 3d0fc8d309
commit 82c23208ee
1 changed files with 14 additions and 2 deletions
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16
docs/reference/commandline/build.md
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@ -425,6 +425,18 @@ Dockerfile are echoed during the build process.
For detailed information on using `ARG` and `ENV` instructions, see the For detailed information on using `ARG` and `ENV` instructions, see the
[Dockerfile reference](../builder.md). [Dockerfile reference](../builder.md).
You may also use the `--build-arg` flag without a value, in which case the value
from the local environment will be propagated into the Docker container being
built:
```bash
$ export HTTP_PROXY=http://10.20.30.2:1234
$ docker build --build-arg HTTP_PROXY .
```
This is similar to how `docker run -e` works. Refer to the [`docker run` documentation](https://docs.docker.com/engine/reference/commandline/run/#set-environment-variables--e---env---env-file)
for more information.
### Optional security options (--security-opt) ### Optional security options (--security-opt)
This flag is only supported on a daemon running on Windows, and only supports This flag is only supported on a daemon running on Windows, and only supports
@ -504,7 +516,7 @@ section in the userguide for more information.
The `--squash` option has a number of known limitations: The `--squash` option has a number of known limitations:
- When squashing layers, the resulting image cannot take advantage of layer - When squashing layers, the resulting image cannot take advantage of layer
sharing with other images, and may use significantly more space. Sharing the sharing with other images, and may use significantly more space. Sharing the
base image is still supported. base image is still supported.
- When using this option you may see significantly more space used due to - When using this option you may see significantly more space used due to
@ -581,7 +593,7 @@ $ docker build --squash -t test .
If everything is right, the history will look like this: If everything is right, the history will look like this:
```bash ```bash
$ docker history test $ docker history test
IMAGE CREATED CREATED BY SIZE COMMENT IMAGE CREATED CREATED BY SIZE COMMENT
4e10cb5b4cac 3 seconds ago 12 B merge sha256:88a7b0112a41826885df0e7072698006ee8f621c6ab99fca7fe9151d7b599702 to sha256:47bcc53f74dc94b1920f0b34f6036096526296767650f223433fe65c35f149eb 4e10cb5b4cac 3 seconds ago 12 B merge sha256:88a7b0112a41826885df0e7072698006ee8f621c6ab99fca7fe9151d7b599702 to sha256:47bcc53f74dc94b1920f0b34f6036096526296767650f223433fe65c35f149eb