macOS binaries do not have -amd64 or other arch suffix (yet)

[sudo6si]

As of Nov 2020 installation of istio-v1.{7,8}.x or asdf install istioctl latest fails because the generated download link is invalid.

You are greeted with following error (because curl -L $download_url yields a Not Found string):

$ asdf install istioctl latest --verbose
Downloading istioctl from https://github.com/istio/istio/releases/download/1.7.4/istio-1.7.4-osx-amd64.tar.gz
bin_install_path: /Users/wadkar/.asdf/installs/istioctl/1.7.4/bin
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100     9  100     9    0     0      6      0  0:00:01  0:00:01 --:--:--     6
tar: Error opening archive: Unrecognized archive format

Following patch works on macOS:

M bin/install
@@ -60,13 +60,17 @@ verlt() {
 }
 
 get_arch() {
-  verlt "$1" 1.6.0 && echo "" || echo "-amd64"
+  if [ "$2" = osx ]; then
+    echo ""
+  else
+    verlt "$1" 1.6.0 && echo "" || echo "-amd64"
+  fi
 }
 
 get_download_url() {
   local version="$1"
   local os_dist="$(get_platform)"
-  local arch="$(get_arch $version)"
+  local arch="$(get_arch "$version" "$os_dist")"
   echo "https://github.com/istio/istio/releases/download/${version}/istio-${version}-${os_dist}${arch}.tar.gz"
 }
 

Of course, feel free to flex your shell-foo and shorten the if conditional to your liking.