Dockerfile

FROM alpine

RUN ls /etc/profile.d /usr/local/bin /usr

COPY resources/etc/ /etc
COPY resources/usr/ /usr

RUN ls /etc/profile.d/ /usr/local/bin /usr

run.sh

mkdir -p resources/etc/profile.d/ resources/usr/local/bin
touch resources/etc/profile.d/my_vars.sh resources/usr/local/bin/my-script

docker build -t test .

Docker behaves really oddly (or at least not how I wanted) when copying a directory under the src of COPY (ADD behaves the same).

This is slightly hard to describe, but essentially when docker is copying in a nested directory it replaces it, rather than copying the files in one-by-one. This means you can't easily copy in many files and merge them with ones existing in the layer for many directories at once.

The output of the first RUN shows some existing files in /etc/profile.d:

 ---> Running in c44e4d25c8f7
/etc/profile.d:
color_prompt

/usr:
bin
lib
local
sbin
share

/usr/local/bin:
 ---> 22b5892e616d
Removing intermediate container 17afb2eae3ba```

Notice how there is a file in `/etc/profile.d` and many under `/usr`.

After we have copied we run the list commands again:

Step 5 : RUN ls /etc/profile.d/ /usr/local/bin /usr
---> Running in dca4ed2024f7
/etc/profile.d/:
color_prompt
my_vars.sh

/usr:
bin
lib
local
sbin
share

/usr/local/bin:
my-script
---> 8bf17bf8dd66

The other dirs in `/usr` are kept, but the whole of `/etc/profile.d` was replaced with just the one we copied in.