how do I parse literals?

[Shadowblitz16]

How do I parse literals like these..
u8
u16
u32
u64
s8
s16
s32
s64

I tried testing my versions of u8 and u16 on a regex site and it doesn't seem to work...

U8 : [0-2][0-2]?[0-5]?;
U16: [0-6][0-5]?[0-5]?[0-3]?[0-5]?;