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