anchor.diff:  
     buildPhase = ''
       set -x
  -    mkdir -p "$out/dev-envs" "$out/nix-support"
  +    mkdir -p "$out/dev-envs" "$out/nix-support" "$out/bin"
       s="$out/nix-support/setup-new-modified"
       cp "$setupNew" "$s"
       # shut some warning up.., do not use set -e
  
positive.code:   # the buildNativeInputs environment variable.
    buildNativeInputs = [ ] ++ buildInputs ;
    name = "env-${name}";
    phases = [ "buildPhase" ];
    setupNew = substituteAll {
      src = ../../stdenv/generic/setup.sh;
      preHook="";
  
negative.code:       export PATH
        echo $name loaded
      EOF
  
      cat >> "$out/bin/load-''${name/env-/}-env" << EOF
      #!/bin/sh
  
      source "$out/dev-envs/''${name/env-/}"
      EOF
      chmod +x "$out/bin/load-''${name/env-/}-env" 
    '';
  }
  