A Survey of $RANDOM
> Most Bourne shell clones support a special RANDOM environment variable that evaluates to a random value between 0 and 32,767 (e.g. 15 bits). Assigment to the variable seeds the generator. This variable is an extension and did not appear in the original Unix Bourne shell. Despite this, the different Bourne-like shells that implement it have converged to the same interface, but only the interface. Each implementation differs in interesting ways. In this article we’ll explore how $RANDOM is implemented in various Bourne-like shells.