Dockerfile：将RUN指令输出到变量中 [英] Dockerfile: Output of RUN instruction into a Variable

问题描述

我正在编写一个dockerfile，并希望将 ls命令的输出放入一个变量，如下所示：

I am writing a dockerfile and want to put the output of the "ls" command into a variable as shown below:

$file = ls /tmp/dir

这里， dir中只有一个文件。

Here, "dir" only has one file inside it.

docker文件中的以下RUN指令不起作用

The following RUN instruction within a dockerfile is not working

RUN $file = ls /tmp/dir

推荐答案

您无法保存一个变量，供以后在其他 Dockerfile 命令中使用（如果您打算这样做）。这是因为每个 RUN 都发生在新的shell中。

You cannot save a variable for later use in other Dockerfile commands (if that is your intention). This is because each RUN happens in a new shell.

但是，如果您只想捕获 ls ，您应该可以在一个 RUN 复合命令中完成此操作。例如：

However, if you just want to capture the output of ls you should be able to do it in one RUN compound command. For example:

RUN file="$(ls -1 /tmp/dir)" && echo $file

或者仅使用subshel​​l内联：

Or just using the subshell inline:

RUN echo $(ls -1 /tmp/dir)

希望这有助于您理解。如果您要解决实际的错误或问题，我可以在此范围内进行扩展，而不是假设的答案。

Hope this helps your understanding. If you have an actual error or problem to solve I could expand on this instead of a hypothetical answer.

完整示例 Dockerfile 表明这将是：

FROM alpine:3.7
RUN mkdir -p /tmp/dir && touch /tmp/dir/file1 /tmp//dir/file2
RUN file="$(ls -1 /tmp/dir)" && echo $file
RUN echo $(ls -1 /tmp/dir)

在构建时您应该看到步骤3和4输出变量（其中包含在步骤2中创建的 file1 和 file2 的列表） ：

When building you should see steps 3 and 4 output the variable (which contains the list of file1 and file2 creating in step 2):

$ docker build --no-cache -t test .
Sending build context to Docker daemon  2.048kB
Step 1/4 : FROM alpine:3.7
 ---> 3fd9065eaf02
Step 2/4 : RUN mkdir -p /tmp/dir && touch /tmp/dir/file1 /tmp//dir/file2
 ---> Running in abb2fe683e82
Removing intermediate container abb2fe683e82
 ---> 2f6dfca9385c
Step 3/4 : RUN file="$(ls -1 /tmp/dir)" && echo $file
 ---> Running in 060a285e3d8a
file1 file2
Removing intermediate container 060a285e3d8a
 ---> 2e4cc2873b8c
Step 4/4 : RUN echo $(ls -1 /tmp/dir)
 ---> Running in 528fc5d6c721
file1 file2
Removing intermediate container 528fc5d6c721
 ---> 1be7c54e1f29
Successfully built 1be7c54e1f29
Successfully tagged test:latest

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