UUIDv4 in swift

import Foundation

guard let f = FileHandle(forReadingAtPath: "/dev/random") else {
    print("Could not open /dev/random")
    exit(1)
}

guard let read = try f.read(upToCount: 16) else {
    print("Could not read any bytes")
    exit(1)
}

if read.count != 16 {
    print("Could not read 16 bytes")
    exit(1)
}

var buf: [UInt8] = Array(read)

// Set bit 6 to 0
buf[8] &= ~(1 << 6)
// Set bit 7 to 1
buf[8] |= 1 << 7

// Set version
buf[6] &= ~(1 << 4)
buf[6] &= ~(1 << 5)
buf[6] |= 1 << 6
buf[6] &= ~(1 << 7)

print(String(format: "%02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-%02x%02x%02x%02x%02x%02x",
             buf[0],
             buf[1],
             buf[2],
             buf[3],
             // -
             buf[4],
             buf[5],
             // -
             buf[6],
             buf[7],
             // -
             buf[8],
             buf[9],
             // -
             buf[10],
             buf[11],
             buf[12],
             buf[13],
             buf[14],
             buf[15]))