Generate version 4 UUID using only /dev/urandom and Bash built-ins

uuidV4.sh

#!/usr/bin/env bash

uuidV4() {
	local LC_ALL=C IFS=
	local byte i
	local -a bytes

	for ((i = 0; i < 16; i++)); do
		read -r -d '' -n1 byte && printf -v byte '%d' "'$byte"
		bytes[i]=$byte
	done </dev/urandom

	bytes[6]=$(( (bytes[6] & 0xf) | 0x40 ))
	bytes[8]=$(( (bytes[8] & 0x3f) | 0x80 ))

	printf '%02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-%02x%02x%02x%02x%02x%02x\n' "${bytes[@]}"
}

uuidV4