src/Pure/System/isabelle_system.scala

     val (result, rc) = bash_output(script)
     if (rc == 0) result
     else error(result)
   }
 
-  def rm_fifo(fifo: String)
-  {
-    bash_output("rm -f '" + fifo + "'")
-  }
+  def rm_fifo(fifo: String): Boolean =
+    (new File(jvm_path(if (Platform.is_windows) fifo + ".lnk" else fifo))).delete
 
   def fifo_input_stream(fifo: String): InputStream =
   {
     if (Platform.is_windows) { // Cygwin fifo as Windows/Java input stream
       val proc = execute(false, expand_path("$ISABELLE_HOME/lib/scripts/raw_dump"), fifo, "-")