anchor.diff:            echo -n "$text" > "$n"
           fi
   
  +        ${checkPhase}
  +
           (test -n "$executable" && chmod +x "$n") || true
         '';
   
  
positive.code:   writeScript = name: text: writeTextFile {inherit name text; executable = true;};
    writeScriptBin = name: text: writeTextFile {inherit name text; executable = true; destination = "/bin/${name}";};
  
  
    # Create a forest of symlinks to the files in `paths'.
    symlinkJoin =
  
negative.code:     , text
      , executable ? false # run chmod +x ?
      , destination ? ""   # relative path appended to $out eg "/bin/foo"
      , checkPhase ? ""    # syntax checks, e.g. for scripts
      }:
      runCommand name
        { inherit text executable;
  