A UUIDv4 generator in REXX.

uuid.rexx

/* A UUIDv4 generator.
 * By [email protected]
 * This should work with any ANSI REXX interpreter,
 * and I *think* it would work with ARexx, but I
 * haven't checked.
 */

/* Store the 16 bytes of random data in a string called bits
 * We will populate this using either using the RANDOM function
 * or by reading from /dev/random, whichever the user requests.
 */
bits = ''

/* Parse the argument to the program. We expect to be invoked
 * either as
 *
 *	generate-uuid RANDOM
 *
 * to generate a UUID pulling randomness from /dev/random, or
 * like
 *
 *	generate-uuid 393820
 *
 * where the provided number is the seed for the internal
 * RANDOM function.
 *
 * For testing purposes, being called with NULL will generate a
 * NULL "random" UUID.
 */
PARSE UPPER ARG mode
SELECT
	WHEN mode = NULL THEN
		CALL GenerateNull

	WHEN mode = RANDOM THEN
		CALL GenerateRandom

	WHEN DATATYPE(mode) = NUM THEN
		CALL GenerateSeeded mode

	OTHERWISE
		SAY "Expected random seed, RANDOM, or NULL"
		EXIT 1
END

/* Our string of bits is populated, so now we can the bits
 * that specify the UUID variant and version.
 *
 * To do this, let's split the string into the parts that
 * are random and the parts that are informational. This
 * illustrates REXX's powerful PARSE instruction.
 */
PARSE VAR bits first +48 version +4 mid +12 variant +2 rest 

/* Recombine everything, specifying version and variant.
 * Note that we use the explicit concatenation operator
 * here.
 */
bits = first || 0100 || mid || 10 || rest

/* Parse it out into the constituent bits. */
PARSE VAR bits first +32 second +16 third +16 fourth +16 rest

/* And output the UUID. This uses REXX's automatic concatenation.
 * Note that we can't have spaces around the quoted dashes, or
 * else we'd have spaces in our output.
 *
 * Also note that ANSI REXX specifically guarantees that we don't
 * suppress left-padding with zeroes when converting from binary
 * to hex. If it didn't, we'd have to do zero padding on the left
 * for each of the segments here.
 */
SAY B2X(first)"-"B2X(second)"-"B2X(third)"-"B2X(fourth)"-"B2X(rest) 

/* And we're done... */
EXIT

/* Our procedure definitoions that get called above. These were
 * factored out as a way to show how to create procedures in REXX;
 * they equally could have been functions or just included inline
 * above.
 */
GenerateNull: PROCEDURE EXPOSE bits
	bits = COPIES(0, 128)
	RETURN

GenerateRandom: PROCEDURE EXPOSE bits
	/* What to do on IO errors... */
	SIGNAL ON NOTREADY

	/* Populate the bit string... */
	DO i = 1 TO 16
		bits = bits || X2B(C2X(CHARIN('/dev/random')))
	END
	RETURN

GenerateSeeded: PROCEDURE EXPOSE bits
	/* Grab our argument. */
	PARSE ARG seed

	/* Seed the random number generator. */
	CALL RANDOM 1, 255, seed

	/* Populate the bitstring... */
	DO i = 1 TO 16
		bits = bits || X2B(C2X(RANDOM(0, 255)))
	END
	RETURN

NOTREADY:
	SAY "Error reading /dev/random"
	EXIT