Cool ways to generate a UUID

OK, may be not cool enough for Linux veterans, but cool enough for me!

There are two ways, in the order of coolness:

1. On Linux only: cat /proc/sys/kernel/random/uuid

   $ cat /proc/sys/kernel/random/uuid
   fa199476-f6f3-4a32-ab89-91d81d9cc319

2. On Linux and macOS: uuidgen

   $ uuidgen
   6180fa98-ddd7-4777-a40d-b548db1f3444

   On macOS, uuidgen gives a UUID in uppercase. You can pipe it to tr command to translate it to lowercase.

   # On macOS
   $ uuidgen
   58D8D68C-B64D-4E1E-AC0F-B00AFAC1E895
   
   $ uuidgen | tr "[:upper:]" "[:lower:]"
   919ae848-df9c-41fa-b59f-de4b933c927c