How to obtain the execution time of a function in Julia?

I want to obtain the execution time of a function in Julia. Here is a minimum working example:

function raise_to(n)
    for i in 1:n
        y = (1/7)^n
    end
end

How to obtain the time it took to execute raise_to(10) ?

The recommended way to benchmark a function is to use BenchmarkTools:

julia> function raise_to(n)
           y = (1/7)^n
       end
raise_to (generic function with 1 method)

julia> using BenchmarkTools

julia> @btime raise_to(10)
  1.815 ns (0 allocations: 0 bytes)

Note that repeating the computation numerous times (like you did in your example) is a good idea to get more accurate measurements. But BenchmarkTools does it for you.

Also note that BenchmarkTools avoids many pitfalls of merely using @time. Most notably with @time, you're likely to measure compilation time in addition to run time. This is why the first invocation of @time often displays larger times/allocations:

# First invocation: the method gets compiled
# Large resource consumption
julia> @time raise_to(10)
  0.007901 seconds (7.70 k allocations: 475.745 KiB)
3.5401331746414338e-9

# Subsequent invocations: stable and low timings
julia> @time raise_to(10)
  0.000003 seconds (5 allocations: 176 bytes)
3.5401331746414338e-9

julia> @time raise_to(10)
  0.000002 seconds (5 allocations: 176 bytes)
3.5401331746414338e-9

julia> @time raise_to(10)
  0.000001 seconds (5 allocations: 176 bytes)
3.5401331746414338e-9