Shell 和 Exec 形式的 Dockerfile 指令的区别 [英] Differences Between Dockerfile Instructions in Shell and Exec Form
问题描述
shell和exec表单有什么区别
CMD:
CMD python my_script.py arg
对比
CMD ["python", "my_script.py", "arg"]
入口点:
ENTRYPOINT ./bin/main
对比
ENTRYPOINT ["./bin/main"]
和运行:
RUN npm start
对比
RUN ["npm", "start"]
Dockerfile 指令?
推荐答案
shell形式和exec形式有两个区别.根据文档，exec 形式是首选形式.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 形式被解析为 JSON 数组，这意味着您必须在单词周围使用双引号 () 而不是单引号 (‘).
The exec form is parsed as a JSON array, which means that you must use double-quotes (") around words not single-quotes (‘).
与 shell 形式不同，exec 形式不调用命令 shell.这意味着不会发生正常的外壳处理.例如，CMD [echo"、$HOME";] 不会对 $HOME 进行变量替换.如果你想要 shell 处理，那么要么使用 shell 形式，要么直接执行 shell，例如:CMD [ "sh", "-c", "echo $HOME";].当使用 exec 形式并直接执行 shell 时，与 shell 形式一样，是 shell 进行环境变量扩展，而不是 docker.
Unlike the shell form, the exec form does not invoke a command shell. This means that normal shell processing does not happen. For example, CMD [ "echo", "$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.
这里还有一些细微之处:
Some additional subtleties here are:
exec 形式可以避免 shell 字符串修改，并使用不包含指定 shell 可执行文件的基本映像运行命令.
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)将单个 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.
There is also a third form for CMD:
CMD [param1",param2"](作为 ENTRYPOINT 的默认参数)
CMD ["param1","param2"] (as default parameters to ENTRYPOINT)
此外，如果您将 CMD 用作要被覆盖的 ENTRYPOINT 的参数/参数，则需要 exec 形式.
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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