Generating Random 15-Character User Name

Generating random 15-character:

$ cat /dev/urandom | env LC_CTYPE=C tr -dc 'a-z0-9' | fold -w 15 | head -n 1

This is the same:

$ $ cat /dev/urandom | env LC_CTYPE=C tr -cd '[:lower:][:digit:]' | fold -w 15 | head -n 1