Create unique random numbers (UUIDs) in bash

I want to create random unique numbers (UUIDs) as the following node.id=ffffffff-ffff-ffff-ffff-ffffffffffff First I tried this $ rndnum= echo $RANDOM"-"echo $RANDOM"-"echo $RANDOM"-"echo $RANDOM"-"echo $RANDOM $ echo $rndnum 30380-echo 21875-echo 14791-echo 32193-echo 11503 What is the right way to create the following (where f is any number)? ffffffff-ffff-ffff-ffff-ffffffffffff