DietPi-PREP | Feature/automated build

[FredericGuilbault]

Status Proof of concept

Add the capability to declare environment variables before script execution to have a non-interactive build. #2745

[MichaIng]

@FredericGuilbault
Many thanks for opening this PR.

I added checks to verify the set environment variables have valid values, otherwise it is reverted to interactive input. This is important since otherwise when some typo or invalid value was set, the script runs into very hard to debug errors or even worse: It runs through without any obvious error and the final image will then run into follow-up errors.

The last 2 commits you did are included as well. We were coding concurrently here 😉.

Testing required:

• Add all environment variables with valid values
• Add all environment variables with invalid values => Revert to interactive input expected
• Add no environment variables

Just a minor side note:

• When coding via editor outside of GitHub, please assure that "tabs" are as well added as tabs with 8 character space. This is our default for scripts on GitHub and also matches the defaults of nano and vim and such.
• Otherwise the alignment will look ugly/broken on GitHub and when opening/editing the script on the DietPi system via cmdline editor.

[MichaIng]

Okay we cannot use G_HW_MODEL, G_GITOWNER etc.
These are set do defaults when dietpi-globals are sourced. So skip the "G_" for environment variables, assign to "G_" values when set and passed validity check.

[MichaIng]

Okay passed tests with all combinations. I will merge.

Changelog: 02e15dc

Many thanks again to @FredericGuilbault for adding this 👍.

[FredericGuilbault]

Cool,
Sorry for the tabs, Looked good on atom and I didin't checked before commit. My bad.

[MichaIng]

@FredericGuilbault
No problem, just a minor visual thing 😉.