Use sudo for symlinks if necessary.

Library/Homebrew/cask/artifact/moved.rb

@@ -82,13 +82,7 @@ module Cask
 
         ohai "Moving #{self.class.english_name} '#{source.basename}' to '#{target}'"
 
-        unless target.dirname.exist?
-          if target.dirname.ascend.find(&:directory?).writable?
-            target.dirname.mkpath
-          else
-            command.run!("/bin/mkdir", args: ["-p", target.dirname], sudo: true)
-          end
-        end
+        Utils.gain_permissions_mkpath(target.dirname, command: command) unless target.dirname.exist?
 
         if target.directory?
           if target.writable?

Library/Homebrew/cask/artifact/symlinked.rb

@@ -43,7 +43,7 @@ module Cask
 
       private
 
-      def link(force: false, **options)
+      def link(force: false, command: nil, **_options)
         unless source.exist?
           raise CaskError,
                 "It seems the #{self.class.link_type_english_name.downcase} " \
@@ -57,26 +57,29 @@ module Cask
           if force && target.symlink? &&
              (target.realpath == source.realpath || target.realpath.to_s.start_with?("#{cask.caskroom_path}/"))
             opoo "#{message}; overwriting."
-            target.delete
+            Utils.gain_permissions_remove(target, command: command)
           else
             raise CaskError, "#{message}."
           end
         end
 
         ohai "Linking #{self.class.english_name} '#{source.basename}' to '#{target}'"
-        create_filesystem_link(**options)
+        create_filesystem_link(command: command)
       end
 
-      def unlink(**)
+      def unlink(command: nil, **)
         return unless target.symlink?
 
         ohai "Unlinking #{self.class.english_name} '#{target}'"
-        target.delete
+        Utils.gain_permissions_remove(target, command: command)
       end
 
-      def create_filesystem_link(command: nil, **_)
-        target.dirname.mkpath
-        command.run!("/bin/ln", args: ["-h", "-f", "-s", "--", source, target])
+      def create_filesystem_link(command: nil)
+        Utils.gain_permissions_mkpath(target.dirname, command: command)
+
+        command.run! "/bin/ln", args: ["-h", "-f", "-s", "--", source, target],
+                                sudo: !target.dirname.writable?
+
         add_altname_metadata(source, target.basename, command: command)
       end
     end

Library/Homebrew/cask/utils.rb

@@ -11,6 +11,17 @@ module Cask
   #
   # @api private
   module Utils
+    def self.gain_permissions_mkpath(path, command: SystemCommand)
+      dir = path.ascend.find(&:directory?)
+      return if path == dir
+
+      if dir.writable?
+        path.mkpath
+      else
+        command.run!("/bin/mkdir", args: ["-p", path], sudo: true)
+      end
+    end
+
     def self.gain_permissions_remove(path, command: SystemCommand)
       if path.respond_to?(:rmtree) && path.exist?
         gain_permissions(path, ["-R"], command) do |p|