In R, what's the simplest way to scale a vector to a unit vector?

Question

In R, what's the simplest way to scale a vector to a unit vector?

For example, suppose

>vec
[1] 1 0 2 1

And

>vec / sqrt(sum(vec^2)) 
[1] 0.4082483 0.0000000 0.8164966 0.4082483

is its unit vector.

Is there some built-in function in R for this?