Dockerfile CMD Shell与exec形式 [英] Dockerfile CMD shell versus exec form

问题描述

docker RUN和CMD语句的shell形式和exec形式之间有什么区别。

What's the difference between the shell form and exec form of docker RUN and CMD statements.

例如：

RUN [ "npm", "start" ]

vs：

RUN npm start 

eg2 ：

CMD ["python","my_script.py","argument"]

vs：

CMD python my_script.py argument 

推荐答案

shell窗体和exec窗体之间有两个区别。根据文档，exec表单是首选形式。这是两个区别：

There are two differences between the shell form and the exec form. According to the documentation, the exec form is the preferred form. These are the two differences:

exec表单被解析为JSON数组，这意味着您必须在非单字周围使用双引号（） -quotes（'）。

The exec form is parsed as a JSON array, which means that you must use double-quotes (") around words not single-quotes (‘).

与shell表单不同，exec表单不会调用命令shell。这意味着正常的外壳处理不会发生。例如，CMD [ echo， $ HOME ]不会在$ HOME上进行变量替换。如果要外壳处理，则可以使用外壳形式，也可以直接执行外壳，例如：CMD [ sh，-c， echo $ HOME）。 ]。在使用exec表单并直接执行shell时（例如在shell表单中），是由shell进行环境变量扩展，而不是docker。

Unlike the shell form, the exec form does not invoke a command shell. This means that normal shell processing does not happen. For example, CMD [ "echo", "$HOME" ] will not do variable substitution on $HOME. If you want shell processing then either use the shell form or execute a shell directly, for example: CMD [ "sh", "-c", "echo $HOME" ]. When using the exec form and executing a shell directly, as in the case for the shell form, it is the shell that is doing the environment variable expansion, not docker.

这里还有其他一些细微之处：

Some additional subtleties here are:

exec形式可以避免shell字符串混乱，并可以使用执行以下操作的基本映像运行命令不包含指定的shell可执行文件。

The exec form makes it possible to avoid shell string munging, and to RUN commands using a base image that does not contain the specified shell executable.

在shell形式中，您可以使用\（反斜杠）将一条RUN指令继续到下一行。

In the shell form you can use a \ (backslash) to continue a single RUN instruction onto the next line.

对于 CMD ：

CMD [ param1， param2]（默认ENTRYPOINT的参数）

CMD ["param1","param2"] (as default parameters to ENTRYPOINT)

此外，如果使用 CMD ，则需要exec表单作为 ENTRYPOINT 的参数/自变量被覆盖。

Additionally, the exec form is required for CMD if you are using it as parameters/arguments to ENTRYPOINT that are intended to be overwritten.

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