Clutch is fine for a mile or two and then no pedal?

Can I ask if the clutch fluid is full? If so, this will be a clutch master cylinder failure because it is bypassing internally. If the fluid level is low, I would check the rear of the clutch master and the bellhousing of the transmission, if fluid is present then the secondary cylinder part has failed. Here is how to change the clutch master out. Check out the images (below). Let us know how it goes.