anchor.diff:  { lib, fetchFromGitHub, makeWrapper, gawk
   , makeFontsConf, freefont_ttf, gnuplot, perl, perlPackages
  +, stdenv, shortenPerlShebang
   }:
   
   let
  
positive.code: 
    outputs = [ "out" ];
  
    nativeBuildInputs = [ makeWrapper gawk ];
  
    buildInputs = [ gnuplot perl ]
      ++ (with perlPackages; [ ListMoreUtils IPCRun StringShellQuote ]);
  
negative.code:   # Tests require gnuplot 4.6.4 and are completely skipped with gnuplot 5.
    doCheck = false;
  
    postInstall = lib.optionalString stdenv.isDarwin ''
      shortenPerlShebang $out/bin/feedgnuplot
    '' + ''
      wrapProgram $out/bin/feedgnuplot \
          --prefix "PATH" ":" "$PATH" \
          --prefix "PERL5LIB" ":" "$PERL5LIB"
  