Conditional COPY/ADD in Dockerfile?

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Here is a simple workaround:

COPY foo file-which-may-exist* /target

Make sure foo exists, since COPY needs at least one valid source.

If file-which-may-exist is present, it will also be copied.

NOTE:
You should take care to ensure that your wildcard doesn’t pick up other files which you don’t intend to copy. To be more careful, you could use file-which-may-exist? instead (? matches just a single character).

Or even better, use a character class like this to ensure that only one file can be matched:

COPY foo file-which-may-exis[t] /target

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