anchor.diff: -{ lib, fetchFromGitHub, makeWrapper
  -, makeFontsConf, freefont_ttf, gnuplot, perl, perlPackages
  -, stdenv, shortenPerlShebang
  +{ lib
  +, fetchFromGitHub
  +, makeWrapper
  +, makeFontsConf
  +, freefont_ttf
  +, gnuplot
  +, perl
  +, perlPackages
  +, stdenv
  +, shortenPerlShebang
  +, installShellFiles
   }:
   
   let
  
positive.code:     wrapProgram $out/bin/feedgnuplot \
          --prefix "PATH" ":" "$PATH" \
          --prefix "PERL5LIB" ":" "$PERL5LIB"
      install -D -m 444 -t $out/share/bash-completion/completions \
          completions/bash/feedgnuplot
      install -D -m 444 -t $out/share/zsh/site-functions \
          completions/zsh/_feedgnuplot
    '';
  
    meta = with lib; {
  
negative.code: 
  perlPackages.buildPerlPackage rec {
    pname = "feedgnuplot";
    version = "1.61";
  
    src = fetchFromGitHub {
      owner = "dkogan";
      repo = "feedgnuplot";
      rev = "v${version}";
      sha256 = "sha256-r5rszxr65lSozkUNaqfBn4I4XjLtvQ6T/BG366JXLRM=";
    };
  
    outputs = [ "out" ];
  
    nativeBuildInputs = [ makeWrapper installShellFiles ] ++ lib.optional stdenv.isDarwin shortenPerlShebang;
  
    buildInputs = [ gnuplot perl ]
      ++ (with perlPackages; [ ListMoreUtils IPCRun StringShellQuote ]);
  