execlineb.nix

let
  execlineb-with-builtins =
    let eldir = "${pkgs.execline}/bin";
    in pkgs.writeScriptBin "execlineb" ''
      #!${eldir}/execlineb -s0
      # appends the execlineb bin dir to PATH if not yet in PATH
      ${eldir}/define eldir ${eldir}
      ''${eldir}/ifelse
      {
        # since this is nix, we can grep for the execline drv hash in PATH
        # to see whether it’s already in there
        ''${eldir}/pipeline
        { ${pkgs.coreutils}/bin/printenv PATH }
        ${pkgs.gnugrep}/bin/grep --quiet "${eldir}"
      }
      # it’s there already
      { ''${eldir}/execlineb $@ }
      # not there yet, add it
      ''${eldir}/importas oldpath PATH
      ''${eldir}/export PATH "''${eldir}:''${oldpath}"
      ''${eldir}/execlineb $@
    '';
in {}