src/Pure/System/isabelle_system.scala

 
     if (gnutar_check) bash("tar " + options + args, redirect = redirect)
     else error("Expected to find GNU tar executable")
   }
 
+  def extract(archive: Path, dir: Path): Unit =
+    archive.get_ext match {
+      case "zip" =>
+        Isabelle_System.bash("unzip -x " + File.bash_path(archive.absolute), cwd = dir.file).check
+      case "tar.gz" | "tgz" =>
+        Isabelle_System.gnutar("-xzf " + File.bash_path(archive), dir = dir).check
+      case _ => error("Cannot extract " + archive)
+    }
+
   def make_patch(base_dir: Path, src: Path, dst: Path, diff_options: String = ""): String = {
     with_tmp_file("patch") { patch =>
       Isabelle_System.bash(
         "diff -ru " + diff_options + " -- " + File.bash_path(src) + " " + File.bash_path(dst) +
           " > " + File.bash_path(patch),