Please add a note that you can't use '-' in variable names

[MattJaccino]

Spent a crazy long time debugging a gitlab script where I tried to assign "exit-code=$?" and had no idea why bash wasn't accepting it. A buddy sent me this repo as a joke, and I noticed it didn't mention this in the VARIABLES section. Definitely would confuse new users since hyphens are allowed in command names.
Thank you.

[ghost]

Good idea. Valid names are, in REGEX: ^(_|[^[:digit:]][[:alnum:]_]+)$