Are URI's a regular language?
Here are some checks you can perform for yourself:


Is there any recursion in the rules?
No: The language is finite, hence regular.
Can the recursions all be written in the form of $A \to \alpha B$, with $\alpha$ a terminal string and $A$, $B$ non-terminals?
Yes: The grammar is (or can be transformed into an equivalent) right-regular (one), hence the language is regular.


If there are constructs like $A \to \alpha B \beta$ or even $A \to \alpha A \beta B \gamma$, then you'll have to look more closely, and there's no easy way: deciding whether a context-free grammar generates a regular language is, in general, undecidable (cf. Greibach's theorem).
See our reference questions for techniques for showing either direction.