【Docker】Dockerfile 格式

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

环境

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

格式

Here is the format of the Dockerfile:

这是 Dockerfile 的格式：

# Comment
INSTRUCTION arguments

The instruction is not case-sensitive. However, convention is for them to be UPPERCASE to distinguish them from arguments more easily.

指令不区分大小写。但是，按约定将它们大写，以便更轻松地将它们与参数区分开。

Docker runs instructions in a Dockerfile in order. A Dockerfile must begin with a FROM instruction. This may be after parser directives, comments, and globally scoped ARGs. The FROM instruction specifies the Parent Image from which you are building. FROM may only be preceded by one or more ARG instructions, which declare arguments that are used in FROM lines in the Dockerfile.

Docker 依次运行在 Dockerfile 中的指令。Dockerfile 必须以 FROM 指令开头。这可能在parser directives，注释和全局范围内的 ARG 之后。FROM 指令指定基础镜像。在 FROM 之前只能有一个或多个 ARG 指令，这些指令声明在 Dockerfile 的 FROM 行中使用的参数。

Docker treats lines that begin with # as a comment, unless the line is a valid parser directive. A # marker anywhere else in a line is treated as an argument. This allows statements like:

除非该行是有效的 parser directives，否则 Docker 会将以 ＃ 号开头的行作为注释。一行中其他任何地方的 ＃ 标记都被视为参数。这允许如下语句：

# Comment
RUN echo 'we are running some # of cool things'

Comment lines are removed before the Dockerfile instructions are executed, which means that the comment in the following example is not handled by the shell executing the echo command, and both examples below are equivalent:

在执行 Dockerfile 指令之前会删除注释行，这意味着以下示例中的注释不会由执行echo 命令的 shell 处理，并且以下两个示例是等效的：

RUN echo hello 
# comment
world

RUN echo hello 
world

Line continuation characters are not supported in comments.

注释中不支持换行符。

空格注意事项

For backward compatibility, leading whitespace before comments (#) and instructions (such as RUN) are ignored, but discouraged. Leading whitespace is not preserved in these cases, and the following examples are therefore equivalent:

为了向后兼容，注释（＃）和指令（例如 RUN）之前的空格将被忽略，但不鼓励使用。在这些情况下，不保留前导空格，因此以下示例是等效的：

        # this is a comment-line
    RUN echo hello
RUN echo world

# this is a comment-line
RUN echo hello
RUN echo world

Note however, that whitespace in instruction arguments, such as the commands following RUN, are preserved, so the following example prints ` hello world` with leading whitespace as specified:

但是请注意，指令参数中的空格（例如 RUN 命令之后的空格）被保留，因此以下示例使用指定的前导空格打印` hello world`：

RUN echo "
     hello
     world

总结

介绍了 Dockerfile 的格式。