參考教程：https://docs.docker.com/engine/reference/builder/
環境
- virtual box 6.1
- centos 7.8
- docker 19.03
RUN
RUN has 2 forms:
RUN 有 2 種格式：
-
RUN <command>(shell form, the command is run in a shell, which by default is/bin/sh -con Linux orcmd /S /Con Windows) -
RUN ["executable", "param1", "param2"](exec form) -
RUN <command>（shell 形式，該命令在 shell 中運行，在 Linux 上默認為/ bin/sh -c，在 Windows 上默認為cmd / S / C） -
RUN ["executable", "param1", "param2"]（exec 形式）
The RUN instruction will execute any commands in a new layer on top of the current image and commit the results. The resulting committed image will be used for the next step in the Dockerfile.
RUN 指令將在當前鏡像頂部的新層中執行所有命令，並提交結果。生成的提交鏡像將用於 Dockerfile 中的下一步。
Layering RUN instructions and generating commits conforms to the core concepts of Docker where commits are cheap and containers can be created from any point in an image’s history, much like source control.
分層運行 RUN 指令並生成提交符合 Docker 的核心概念，在 Docker 上，提交很廉價，並且可以從鏡像歷史記錄的任何位置創建容器，就像源代碼控制一樣。
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.
exec 形式可以避免破壞 shell 字符串，並可以使用不包含指定 shell 可執行文件的基礎鏡像執行 RUN 命令。
The default shell for the shell form can be changed using the SHELL command.
可以使用 SHELL 命令更改 shell 格式的默認 shell。
In the shell form you can use a \ (backslash) to continue a single RUN instruction onto the next line. For example, consider these two lines:
在 shell 格式中，您可以使用 \（反斜杠）將一條 RUN 指令繼續到下一行。例如，考慮以下兩行：
RUN /bin/bash -c 'source $HOME/.bashrc; \
echo $HOME'
Together they are equivalent to this single line:
它們在一起等效於以下這一行：
RUN /bin/bash -c 'source $HOME/.bashrc; echo $HOME'
To use a different shell, other than ‘/bin/sh’, use the exec form passing in the desired shell. For example:
要使用 /bin/sh 以外的其他 shell，請使用 exec 形式傳入所需的 shell。例如：
RUN ["/bin/bash", "-c", "echo hello"]
Note
The exec form is parsed as a JSON array, which means that you must use double-quotes (“) around words not single-quotes (‘).
注意
exec 形式被解析為 JSON 數組，這意味着您必須使用雙引號（"）而不是單引號（'）來包圍單詞。
Unlike the shell form, the exec form does not invoke a command shell. This means that normal shell processing does not happen. For example, RUN [ "echo", "$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: RUN [ "sh", "-c", "echo $HOME" ]. When using the exec form and executing a shell directly, as in the case for the shell form, it is the shell that is doing the environment variable expansion, not docker.
與 shell 格式不同，exec 格式不調用命令外殼程序。這意味着不會進行常規的外殼處理。例如，RUN [ "echo", "$HOME" ] 不會在 $HOME 上進行變量替換。如果要進行 shell 處理，則可以使用 shell 形式或直接執行 shell，例如： RUN [ "sh", "-c", "echo $HOME" ]。當使用 exec 格式並直接執行 shell 時，是由 shell 進行環境變量擴展，而不是 docker。
Note
In the JSON form, it is necessary to escape backslashes. This is particularly relevant on Windows where the backslash is the path separator. The following line would otherwise be treated as shell form due to not being valid JSON, and fail in an unexpected way:
RUN ["c:\windows\system32\tasklist.exe"]The correct syntax for this example is:
RUN ["c:\\windows\\system32\\tasklist.exe"]
注意
在 JSON 格式中，必須轉義反斜杠。這在 Windows 中特別有用，在 Windows 中反斜杠是路徑分隔符。由於無效的 JSON，以下行否則將被視為 shell 形式，並以意外的方式失敗：
RUN ["c:\windows\system32\tasklist.exe"]此示例的正確語法為：
RUN ["c:\\windows\\system32\\tasklist.exe"]
The cache for RUN instructions isn’t invalidated automatically during the next build. The cache for an instruction like RUN apt-get dist-upgrade -y will be reused during the next build. The cache for RUN instructions can be invalidated by using the --no-cache flag, for example docker build --no-cache.
在下次構建期間，RUN 指令的緩存不會自動失效。諸如 RUN apt-get dist-upgrade -y 之類的指令的緩存將在下一次構建中重用。可以通過使用 --no-cache 標志來使 RUN 指令的緩存無效，例如 docker build --no-cache。
See the Dockerfile Best Practices guide for more information.
有關更多信息，請參閱 Dockerfile 最佳實踐指南。
The cache for RUN instructions can be invalidated by ADD and COPY instructions.
示例
Dockerfile 文件
FROM busybox
ENV name=jiangbo
RUN echo $name
RUN echo "---------------"
RUN ["/bin/sh","-c","echo $name"]
構建結果
[root@master env]# docker build . --no-cache
Sending build context to Docker daemon 3.584kB
Step 1/5 : FROM busybox
---> dc3bacd8b5ea
Step 2/5 : ENV name=jiangbo
---> Running in eee44fef26f6
Removing intermediate container eee44fef26f6
---> 947038c832dc
Step 3/5 : RUN echo $name
---> Running in 26e9d42ced2a
jiangbo
Removing intermediate container 26e9d42ced2a
---> a55b1d062caa
Step 4/5 : RUN echo "---------------"
---> Running in 2b3455b3b565
---------------
Removing intermediate container 2b3455b3b565
---> 314567362777
Step 5/5 : RUN ["/bin/sh","-c","echo $name"]
---> Running in 7ebe6c03686d
jiangbo
Removing intermediate container 7ebe6c03686d
---> 2c6b18b8be36
Successfully built 2c6b18b8be36
[root@master env]#
總結
介紹了 Dockerfile 中 RUN 指令的使用。