title: How not to remake pre-requisites when final target exists with Make
body: <p>In the following Makefile, I would like make not to remake the ALL md5 files when the final file: checksums.md5 already exists:</p>
  
  <pre><code>SOURCEDIR := .
  SOURCES := $(shell find $(SOURCEDIR) -name '*.gz')
  STAGES := .md5
  CAT := checksums.md5
  ALL := $(foreach I, $(STAGES), $(addsuffix $I, $(SOURCES)))
  
  all : ${CAT}
  
  %.md5: %
      md5sum $&lt; &gt; $@
  
  ${CAT} : ${ALL}
      cat $^ &gt;&gt; $@
      rm *gz.md5
  </code></pre>