Add support for readlink on macOS

rsync_ui.sh

@@ -2,7 +2,15 @@
 
 set -e
 
-ATTRACT_DIR="$(dirname "$(readlink -f "$0")")"
+# macOS does not support readlink -f, so we use greadlink instead
+if [[ `uname` == 'Darwin' ]]; then
+    ash greadlink 2>/dev/null || { echo >&2 "Install greadlink using brew."; exit 1; }
+    readlink='grealink'
+else
+    readlink='readlink'
+fi
+
+ATTRACT_DIR="$(dirname "$($readlink -f "$0")")"
 if [ ! -d "$ATTRACT_DIR" ]; then
     echo "Unable to find Attract dir '$ATTRACT_DIR'"
     exit 1