Match an Array in F#

The closest thing you'll get without converting to a list is:

match argv with
| arr when argv.Length > 0 ->
    let first = arr.[0]
    printfn "%s" first
| _ -> printfn "none"

If you convert argv to a list using Array.toList, you can then pattern match on it as a list using the cons operator, :::

match argv |> Array.toList with
    | x::[]  -> printfn "%s" x
    | x::xs  -> printfn "%s, plus %i more" x (xs |> Seq.length)
    | _  -> printfn "nothing"

You can use truncate:

match args |> Array.truncate 1 with
| [| x |] -> x
| _       -> "No arguments"