anchor.diff:      sha256 = checksum;
     };
   
  -  buildInputs = [ wget perl MojoIOLoopForkCall-0-17 perlPackages.TAPParserSourceHandlerpgTAP ];
  +  buildInputs = [ wget perl MojoIOLoopForkCall-0-20 perlPackages.TAPParserSourceHandlerpgTAP ];
   
  -  nativeBuildInputs = [ autoconf automake ];
  +  nativeBuildInputs = [ autoconf automake autoreconfHook ];
   
     preConfigure = ''
       sed -i 's/^SUBDIRS =.*$/SUBDIRS = lib/' Makefile.am
  
positive.code: { stdenv, fetchFromGitHub, fetchurl, perl, perlPackages, wget, autoconf, automake }:
  
  let
    # when upgrade znapzend, check versions of Perl libs here: https://github.com/oetiker/znapzend/blob/master/PERL_MODULES
    Mojolicious-6-46 = perlPackages.buildPerlPackage rec {
      pname = "Mojolicious";
      version = "6.46";
      src = fetchurl {
        url = "mirror://cpan/authors/id/S/SR/SRI/${pname}-${version}.tar.gz";
        sha256 = "0i3axmx4506fx5gms148pj65x6ys7flaz1aqjd8hd9zfkd8pzdfr";
      };
    };
    MojoIOLoopForkCall-0-17 = perlPackages.buildPerlModule rec {
      pname = "Mojo-IOLoop-ForkCall";
      version = "0.17";
      src = fetchurl {
        url = "mirror://cpan/authors/id/J/JB/JBERGER/${pname}-${version}.tar.gz";
        sha256 = "090qxz1nbah2qxvfg4whl6yp6q03qkx7a42751iai521nk1yavc8";
      };
      propagatedBuildInputs = [ perlPackages.IOPipely Mojolicious-6-46 ];
    };
  
    version = "0.18.0";
    checksum = "1nlvw56viwgafma506slywfg54z6009jmzc9q6wljgr6mqfmmchd";
  in
  stdenv.mkDerivation {
    pname = "znapzend";
  
negative.code:   postInstall = ''
      substituteInPlace $out/bin/znapzend --replace "${perl}/bin/perl" \
        "${perl}/bin/perl \
        -I${Mojolicious-8-35}/${perl.libPrefix} \
        -I${perlPackages.TAPParserSourceHandlerpgTAP}/${perl.libPrefix} \
        -I${MojoIOLoopForkCall-0-20}/${perl.libPrefix} \
        -I${perlPackages.IOPipely}/${perl.libPrefix} \
        "
      substituteInPlace $out/bin/znapzendzetup --replace "${perl}/bin/perl" \
        "${perl}/bin/perl \
        -I${Mojolicious-8-35}/${perl.libPrefix} \
        -I${perlPackages.TAPParserSourceHandlerpgTAP}/${perl.libPrefix} \
        -I${MojoIOLoopForkCall-0-20}/${perl.libPrefix} \
        -I${perlPackages.IOPipely}/${perl.libPrefix} \
        "
      substituteInPlace $out/bin/znapzendztatz --replace "${perl}/bin/perl" \
        "${perl}/bin/perl \
        -I${Mojolicious-8-35}/${perl.libPrefix} \
        -I${perlPackages.TAPParserSourceHandlerpgTAP}/${perl.libPrefix} \
        -I${MojoIOLoopForkCall-0-20}/${perl.libPrefix} \
        -I${perlPackages.IOPipely}/${perl.libPrefix} \
        "
    '';
  