> I noticed you start to find every operating system quirk ever when you start writing Dockerfiles.

I've been using Dockerfiles extensively for years and I'm yet to find anything that fits the definition of a OS quirk.

The quirkiest thing I've noticed in Dockerfiles is the ADD vs COPY thing.

> I've run into so many strange things just converting a simple predictable shell script into a Dockerfile.

What exactly are you trying to do setting up a Dockerfile that requires a full blown shell script?

A Dockerfile should have little more beyond updating/installing system packages with a package manager, and copying files into the container image. First you run a build to get your artifacts ready for packaging, and afterwards you package those artifacts by running your Dockerfile.