title: What does $$@ and the pipe symbol in Makefile stand for?
body: <p>In the following Makefile definition:</p>
  <ol>
  <li>What does the <code>$$@</code> in the second last line stand for?</li>
  <li>What about the <code>|</code> symbol in the middle line?</li>
  </ol>
  
  <pre><code>define KERNEL_RULE
  $(DESTDIR)/$(1) : kernel_modules
  $(DEST_DIR)/$(1) : $(SOURCE_DIR)/$(1) | $(DEST_DIR)
      cp $(SOURCE_DIR)/$(1) $$@
  endef
  </code></pre>