Maybe you can use ARG to help you, like this:
Dockerfile:
FROM jfloff/alpine-python:2.7
ARG src="https://stackoverflow.com/questions/56420386/Folder 1/File.txt"
ARG target="Dir 1/"
COPY ${src} ${target}
BTW, a / has to be add at the end of Dir 1 if you treat really want to treat it as a folder.
And, JSON format is also ok, just you miss ,, it should be:
FROM jfloff/alpine-python:2.7
COPY ["https://stackoverflow.com/questions/56420386/Folder 1/File.txt", "Dir 1/"]
Update for your comments:
In official guide, it said:
When copying files or directories that contain special characters (such as [ and ]), you need to escape those paths following the Golang rules to prevent them from being treated as a matching pattern.
So, for your case, it should be:
FROM jfloff/alpine-python:2.7
ARG src="https://stackoverflow.com/questions/56420386/[[]Folder 1]/__SLIM_TEMPLATE.mm"
ARG target="[Folder 1]/"
COPY ${src} ${target}
Or:
FROM jfloff/alpine-python:2.7
COPY ["https://stackoverflow.com/questions/56420386/[[]Folder 1]/__SLIM_TEMPLATE.mm", "[Folder 1]/"]