Conventions for bash/shell code and one-off commands, in scripts or ad-hoc terminal use.
Use lowercase (or snake_case) for ordinary shell variables: block=$(cat file.json), not BLOCK=$(cat file.json). Reserve all-caps names for variables that are actually exported as environment variables (export PATH=..., NOTES_URL read by a script via os.getenv, etc.) or that are genuine shell built-ins/conventions (HOME, PATH).
Why: all-caps is the long-standing convention for environment variables specifically. Using it for a plain local variable (a temp holder for a JSON blob, a loop counter, a path) is misleading -- it signals "this is exported / read by another process" when it isn't.