Description
Is this a docs issue?
- My issue is about the documentation content or website
Type of issue
Information is incorrect
Description
In the documentation for the ENV instruction, there is an example that reads:
If an environment variable is only needed during build, and not in the final image, consider setting a value for a single command instead:
RUN DEBIAN_FRONTEND=noninteractive apt-get update && apt-get install -y ...
I think that suggestion is misleading, as IIUC DEBIAN_FRONTEND is only defined for the first command apt-get update and not for the apt-get install step. It is therefore not equivalent to the examples that use ENV or ARG.
Example demonstrating the problem:
$ FOO=bar printenv FOO PATH && echo 123 && printenv FOO PATH
bar
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
123
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/binIn the above example, FOO is defined only in the first call to printenv.
Location
https://docs.docker.com/reference/dockerfile/
Suggestion
Perhaps the most obvious solution is to repeat DEBIAN_FRONTEND:
RUN DEBIAN_FRONTEND=noninteractive apt-get update && DEBIAN_FRONTEND=noninteractive apt-get install -y ...
For this particular use case in which the environment variable needs to be available to multiple commands but not be persistent in the final image, I'd emphasize the use of ARG instead, as it is less error-prone.