How to find manual doc for bash $RANDOM special variable?

In Bash there are some variables (like $RANDOM) which are builtin functions. My understanding is that $RANDOM uses the C function random (e.g. man random).

But I had to stumble across that information. What I wanted to be able to do was something like man $RANDOM or type $RANDOM (or even help $RANDOM).

The problem with trying that is $RANDOM gets evaluated to the actual random number :-)

So how do you identify what the implementation is for a special builtin variable like $RANDOM? Other than sifting through Bash source code, which I just don't have the brain capacity for.

Surely there's a way to get the shell to indicate what implementation a special variable has (e.g. "this is a builtin variable that points to a C function of <N> name")

Or maybe there isn't? *shrugs*

Any help/info on this would be appreciated :-)

Thanks!

Solution

from man bash, /RANDOM

RANDOM Each time this parameter is referenced, a random integer between 0 and 32767 is generated.  The sequence of random numbers may be initialized by assigning a value to RANDOM.  If RANDOM is unset, it loses its
       special properties, even if it is subsequently reset.

manual doesn't say how it is implemented.

Otherwise from sources : variables.c shows that RANDOM is linked to function get_random

INIT_DYNAMIC_VAR ("RANDOM", (char *)NULL, get_random, assign_random);

which calls get_random_number, seedrand and brand

/* A linear congruential random number generator based on the example
   one in the ANSI C standard.  This one isn't very good, but a more
   complicated one is overkill. */

/* Returns a pseudo-random number between 0 and 32767. */
static int
brand ()
{
  /* From "Random number generators: good ones are hard to find",
     Park and Miller, Communications of the ACM, vol. 31, no. 10,
     October 1988, p. 1195. filtered through FreeBSD */
  long h, l;

  /* Can't seed with 0. */
  if (rseed == 0)
    rseed = 123459876;
  h = rseed / 127773;
  l = rseed % 127773;
  rseed = 16807 * l - 2836 * h;
#if 0
  if (rseed < 0)
    rseed += 0x7fffffff;
#endif
  return ((unsigned int)(rseed & 32767));       /* was % 32768 */
}