Docker echo环境变量 [英] Docker echo environment variable

问题描述

我正在尝试编写一个小的docker文件，该文件设置了一个User，只是回显了当前用户，作为一个小例子来向自己证明它正在运行。我尝试了许多变体，但在文档中找不到太多帮助。

I'm trying to write a little docker file that sets a User and just echos the current user as a little example to prove to myself it is working. I've tried a number of variants and couldn't find much help in the documentation.

FROM ubuntu
USER daemon
# ENTRYPOINT ["echo", "$USER"]
# just gives "$USER"
# ENTRYPOINT ["echo", "-e", "${USER}"]
# just gives "$USER"
# ENTRYPOINT echo $USER
# gives empty string
# ENTRYPOINT ["/bin/echo", "$USER"]
# just gives "$USER"

我正在运行 docker build 。在dockerfile上，然后运行 docker run< image-id> 并获取结果

I'm running docker build . on the dockerfile and then running docker run <image-id> and getting the results

预期结果是守护程序，或者没有 USER守护程序行，我希望根。

Expected result is daemon, or without the USER daemon line, I expect root. Probably a really simple answer.

推荐答案

这是预期的行为，看起来很奇怪！

This is the expected behavior, as weird as it seems!

当 ENTRYPOINT 是列表时（如 ENTRYPOINT [ echo， $ USER] ），按原样使用，无需进一步解析或解释。因此， $ USER 仍然是 $ USER ，因为在此过程中没有涉及用Shell值替换它的shell。 USER 环境变量。

When ENTRYPOINT is a list (as in ENTRYPOINT ["echo", "$USER"]), it is used as-is, without further parsing or interpretation. So $USER remains $USER, because there is no shell involved in the process to replace it with the value of the USER environment variable.

现在，当 ENTRYPOINT 为一个字符串（如 ENTRYPOINT echo $ USER ），实际执行的是 sh -c echo $ USER ，并且 $ USER 被环境变量的值替换（如您所愿）。

Now, when ENTRYPOINT is a string (as in ENTRYPOINT echo $USER), what is actually executed is sh -c "echo $USER", and $USER is replaced with the value of the environment variable (as you would expect).

但是，默认情况下未设置环境变量 USER 。它由登录过程设置；而当您只运行 sh -c ... 时，不涉及登录过程。

However, the environment variable USER is not set by default. It is set by the login process; and when you just run sh -c ... the login process is not involved.

比较环境时运行 docker run -t -i ubuntu bash 和 docker run -t -i ubuntu login -f root 。在前一种情况下，您将获得一个非常基本的环境。在后一种情况下，您将获得习惯的完整环境（包括 USER 变量）。

Compare the environment when running docker run -t -i ubuntu bash and docker run -t -i ubuntu login -f root. In the former case, you will get a very basic environment; in the latter case, you will get the complete environment that you are used to (including USERvariable).

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