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

View File

@ -425,6 +425,18 @@ Dockerfile are echoed during the build process.
For detailed information on using `ARG` and `ENV` instructions, see the
[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)
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:
- 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
base image is still supported.
- 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:
```bash
$ docker history test
$ docker history test
IMAGE CREATED CREATED BY SIZE COMMENT
4e10cb5b4cac 3 seconds ago 12 B merge sha256:88a7b0112a41826885df0e7072698006ee8f621c6ab99fca7fe9151d7b599702 to sha256:47bcc53f74dc94b1920f0b34f6036096526296767650f223433fe65c35f149eb