參考教程：https://docs.docker.com/engine/reference/builder/

環境

1. virtual box 6.1
2. centos 7.8
3. docker 19.03

ENV

ENV <key>=<value> ...

The ENV instruction sets the environment variable <key> to the value <value>. This value will be in the environment for all subsequent instructions in the build stage and can be

ENV 指令將環境變數 <key> 設定為值 <value>。此值將在構建階段的所有後續指令的環境中使用，也可以在很多情況下

Example:

例如：

ENV MY_NAME="John Doe"
ENV MY_DOG=Rex\ The\ Dog
ENV MY_CAT=fluffy

The ENV instruction allows for multiple <key>=<value> ... variables to be set at one time, and the example below will yield the same net results in the final image:

ENV 指令允許一次設定多個 <key> = <value> ... 變數，下面的示例將在最終映象中產生相同的最終結果：

ENV MY_NAME="John Doe" MY_DOG=Rex\ The\ Dog \
    MY_CAT=fluffy

The environment variables set using ENV will persist when a container is run from the resulting image. You can view the values using docker inspect, and change them using docker run --env <key>=<value>.

當從結果映象執行容器時，使用 ENV 設定的環境變數將保留。您可以使用 docker inspect 檢視值，並使用 docker run --env <key> = <value> 更改它們。

Environment variable persistence can cause unexpected side effects. For example, setting ENV DEBIAN_FRONTEND=noninteractive changes the behavior of apt-get, and may confuse users of your image.

環境變數的永續性可能導致意外的副作用。例如，設定 ENV DEBIAN_FRONTEND=noninteractive 會更改 apt-get 的行為，並可能使映象使用者感到困惑。

If an environment variable is only needed during build, and not in the final image, consider setting a value for a single command instead:

如果僅在構建過程中需要環境變數，而在最終映像中則不需要，請考慮為單個命令設定一個值：

RUN DEBIAN_FRONTEND=noninteractive apt-get update && apt-get install -y ...

Or using ARG, which is not persisted in the final image:

或使用 ARG，它不會保留在最終映象中：

ARG DEBIAN_FRONTEND=noninteractive
RUN apt-get update && apt-get install -y ...

Alternative syntax

替代語法

The ENV instruction also allows an alternative syntax ENV <key> <value>, omitting the =. For example:

ENV 指令還允許使用替代語法 ENV <key> <value>，而忽略 =。例如：

ENV MY_VAR my-value

This syntax does not allow for multiple environment-variables to be set in a single ENV instruction, and can be confusing. For example, the following sets a single environment variable (ONE) with value "TWO= THREE=world":

這種語法不允許在單個 ENV 指令中設定多個環境變數，這可能會造成混淆。例如，以下程式碼將單個環境變數（ONE）的值設定為 "TWO= THREE=world"：

ENV ONE TWO= THREE=world

The alternative syntax is supported for backward compatibility, but discouraged for the reasons outlined above, and may be removed in a future release.

支援備用語法以實現向後相容，但出於上述原因，不建議使用該語法，並且在將來的版本中可能會刪除該語法。

示例

Dockerfile 檔案

FROM busybox
LABEL author=jiangbo
ENV name=jiangbo
CMD echo $name

構建結果

[root@master env]# docker build -t jiangbo:0.0.1 .
Sending build context to Docker daemon  3.584kB
Step 1/4 : FROM busybox
 ---> dc3bacd8b5ea
Step 2/4 : LABEL author=jiangbo
 ---> Running in e7a093e0fc49
Removing intermediate container e7a093e0fc49
 ---> 8129cae696ad
Step 3/4 : ENV name=jiangbo
 ---> Running in 8bdcffbe711e
Removing intermediate container 8bdcffbe711e
 ---> c8a646bfdab3
Step 4/4 : CMD echo $name
 ---> Running in 9cfc4f234843
Removing intermediate container 9cfc4f234843
 ---> b6f80c7fac3f
Successfully built b6f80c7fac3f
Successfully tagged jiangbo:0.0.1

檢視結果

[root@master env]# docker run jiangbo:0.0.1
jiangbo

總結

介紹了 Dockerfile 中 ENV 指令的使用。