Como tornar o binário no pacote Nix já existente capaz de executar um script de shell em outro pacote?

Atualmente estou empacotando um driver de impressora, que usa um script de shell como filtro CUPS. Obviamente, o CUPS precisa ser capaz de executar esse script. Atualmente, no entanto, está me dando um erro de formato exec ao tentar. O script shell começa com um #!/bin/shshebang.

O código a seguir para o pacote vai ser muito feio/hacky porque meu conhecimento do Nix é muito básico, então desculpe antecipadamente. Se você quiser fornecer sugestões para torná-lo melhor, vá em frente, mas estou mais preocupado em como fazê-lo funcionar por enquanto.

with import <nixpkgs> {};

let
  srcs = {
    lpr-deb = fetchurl {
      url = "http://download.brother.com/welcome/dlf101620/mfc9332cdwlpr-1.1.3-0.i386.deb";
      sha256 = "0mmqcwpbw4dx2hqaxhnvm52jm84vq8c55xrixsvapxwrdbpkdcca";
      name = "mfc9332cdwlpr-1.1.3-0.i386.deb";
    };
    cupswrapper-deb = fetchurl {
      url = "http://download.brother.com/welcome/dlf101621/mfc9332cdwcupswrapper-1.1.4-0.i386.deb";
      sha256 = "1q9y90hdrgl80zwqk2vn7b1znjvf15l8q0zg868sv0by6rdq8r5w";
      name = "mfc9332cdwcupswrapper-1.1.4-0.i386.deb";
    };
  };
in stdenv.mkDerivation rec {
  name="brother-mfc9332cdw";
  rev = "1.1.4-0";

  buildInputs = [ pkgs.wget pkgs.dpkg pkgs.perl pkgs.bash ];

  unpackPhase = ''
    dpkg-deb -x ${srcs.lpr-deb} .
    dpkg-deb -x ${srcs.cupswrapper-deb} .
    '';

  dontBuild = true;

  installPhase = ''
    perl -i -pe 's#printcap\.local#printcap#g' opt/brother/Printers/mfc9332cdw/inf/setupPrintcapij
    cp -rf usr $out/
    cp -rf opt $out/
    mkdir -p $out/share/cups/model/Brother
    cp $out/opt/brother/Printers/mfc9332cdw/cupswrapper/brother_mfc9332cdw_printer_en.ppd $out/share/cups/model/Brother
    chmod 644 $out/share/cups/model/Brother/brother_mfc9332cdw_printer_en.ppd
    cat $out/opt/brother/Printers/mfc9332cdw/cupswrapper/cupswrappermfc9332cdw | sed -n "/ENDOFWFILTER/,/ENDOFWFILTER/p" | tail -n +2 | sed "$ d" > brother_lpdwrapper_mfc9332cdw
    perl -i -pe 's#/usr/#$out/#g' brother_lpdwrapper_mfc9332cdw && perl -i -pe 's#/opt/#$out/opt/#g' brother_lpdwrapper_mfc9332cdw
    cat <<!ENDOFWFILTER! > brother_lpdwrapper_mfc9332cdw
      #!/bin/sh
      #
      # Copyright (C) 2005-2016 Brother. Industries, Ltd.
      #                                    Ver1.10

      # This program is free software; you can redistribute it and/or modify it
      # under the terms of the GNU General Public License as published by the Free
      # Software Foundation; either version 2 of the License, or (at your option)
      # any later version.
      #
      # This program is distributed in the hope that it will be useful, but WITHOUT
      # ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
      # FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
      # more details.
      #
      # You should have received a copy of the GNU General Public License along with
      # this program; if not, write to the Free Software Foundation, Inc., 59 Temple
      # Place, Suite 330, Boston, MA  02111-1307  USA
      #

      LOGFILE="/dev/null"
      LOGLEVEL="1"
      LOGCLEVEL="7"
      DEBUG=0
      NUPENABLE=1
      LOG_LATESTONLY=1


      touch /tmp/mfc9332cdw_latest_print_info
      chmod 600 -R /tmp/mfc9332cdw_latest_print_info

      errorcode=0

      if [ \$DEBUG != 0 ]; then
          LOGFILE=/tmp/br_cupsfilter_debug_log
      fi

      PPDC=\`printenv | grep "PPD="\`
      PPDC=\`echo \$PPDC | sed -e 's/PPD=//'\`

      if [ "\$PPDC" = "" ]; then
          PPDC="$out/share/cups/model/Brother/brother_mfc9332cdw_printer_en.ppd"
      fi


      if [ \$LOGFILE != "/dev/null" ]; then
        if [ \$LOG_LATESTONLY == "1" ]; then
          rm -f \$LOGFILE
          date                                                           >\$LOGFILE
        else
          if [ -e \$LOGFILE ]; then
              date                                                        >>\$LOGFILE
          else
              date                                                        >\$LOGFILE
          fi
        fi
          echo "arg0 = \$0"                                           >>\$LOGFILE
          echo "arg1 = \$1"                                           >>\$LOGFILE
          echo "arg2 = \$2"                                           >>\$LOGFILE
          echo "arg3 = \$3"                                           >>\$LOGFILE
          echo "arg4 = \$4"                                           >>\$LOGFILE
          echo "arg5 = \$5"                                           >>\$LOGFILE
          echo "arg6 = \$6"                                           >>\$LOGFILE
          echo "PPD  = \$PPD"                                         >>\$LOGFILE
      fi

      cp  $out/opt/brother/Printers/mfc9332cdw/inf/brmfc9332cdwrc  /tmp/brmfc9332cdwrc_\$$
      chmod 777 -R /tmp/brmfc9332cdwrc_\$$
      export BRPRINTERRCFILE=/tmp/brmfc9332cdwrc_\$$

      INPUT_TEMP_PS=\`mktemp /tmp/br_input_ps.XXXXXX\`

      nup="cat"
      if [ "\`echo \$5 | grep 'Nup='\`" != "" ] && [ \$NUPENABLE != 0 ]; then

          if   [ "\`echo \$5 | grep 'Nup=64'\`" != "" ]; then
              nup="psnup -64"
          elif [ "\`echo \$5 | grep 'Nup=32'\`" != "" ]; then
              nup="psnup -32"
          elif [ "\`echo \$5 | grep 'Nup=25'\`" != "" ]; then
              nup="psnup -25"
          elif [ "\`echo \$5 | grep 'Nup=16'\`" != "" ]; then
              nup="psnup -16"
          elif [ "\`echo \$5 | grep 'Nup=8'\`" != "" ]; then
              nup="psnup -8"
          elif [ "\`echo \$5 | grep 'Nup=6'\`" != "" ]; then
              nup="psnup -6"
          elif [ "\`echo \$5 | grep 'Nup=4'\`" != "" ]; then
              nup="psnup -4"
          elif [ "\`echo \$5 | grep 'Nup=2'\`" != "" ]; then
              nup="psnup -2"
          elif [ "\`echo \$5 | grep 'Nup=1'\`" != "" ]; then
              nup="cat"
          fi
          echo   "NUP=\$nup"                                      >>\$LOGFILE
         if [ -e /usr/bin/psnup ]; then
             if [ \$# -ge 7 ]; then
                 cat \$6  | \$nup > \$INPUT_TEMP_PS
             else
                 cat       | \$nup > \$INPUT_TEMP_PS
             fi
         else
             if [ \$# -ge 7 ]; then
                 cp \$6  \$INPUT_TEMP_PS
             else
                 cat    > \$INPUT_TEMP_PS
             fi
         fi
      else
         if [ \$# -ge 7 ]; then
            cp \$6  \$INPUT_TEMP_PS
         else
            cat    > \$INPUT_TEMP_PS
         fi
      fi
      if [ -e "$out/opt/brother/Printers/mfc9332cdw/lpd/filtermfc9332cdw" ]; then
             :
      else
          echo "ERROR: /opt/brother/Printers/mfc9332cdw/lpd/filtermfc9332cdw does not exist"   >>\$LOGFILE
          echo "ERROR: /opt/brother/Printers/mfc9332cdw/lpd/filtermfc9332cdw does not exist"   >>/tmp/mfc9332cdw_latest_print_info
          errorcode=30
          exit
      fi

      CUPSOPTION=\`echo "\$5 Copies=1" | sed -e 's/BrMirror=OFF/MirrorPrint=OFF/' -e 's/BrMirror=ON/MirrorPrint=ON/' -e 's/BrChain/Chain/' -e 's/BrBrightness/Brightness/' -e 's/BrContrast/Contrast/' -e 's/BrHalfCut/HalfCut/' -e 's/BrAutoTapeCut/AutoCut/' -e 's/BrHalftonePattern/Halftone/' -e 's/Binary/Binary/' -e 's/Dither/Dither/' -e 's/ErrorDiffusion/ErrorDiffusion/' -e 's/BrSheets/Sheets/' -e 's/multiple-document-handling/Collate/' -e 's/separate-documents-collated-copies/ON/' -e 's/separate-documents-uncollated-copies/OFF/'\`
      if [ -e "$out/opt/brother/Printers/mfc9332cdw/cupswrapper/brcupsconfpt1" ]; then

        if [ \$DEBUG = 0 ]; then
           $out/opt/brother/Printers/mfc9332cdw/cupswrapper/brcupsconfpt1  MFC9332CDW  \$PPDC 0 "\$CUPSOPTION" "mfc9332cdw" \$BRPRINTERRCFILE>> /dev/null
        else
           $out/opt/brother/Printers/mfc9332cdw/cupswrapper/brcupsconfpt1  MFC9332CDW  \$PPDC \$LOGCLEVEL "\$CUPSOPTION" "mfc9332cdw" \$BRPRINTERRCFILE>>\$LOGFILE
        fi
      fi

      if [ \$DEBUG -lt 10 ]; then
          cat    \$INPUT_TEMP_PS | $out/opt/brother/Printers/mfc9332cdw/lpd/filtermfc9332cdw 
          echo brmfc9332cdwrc_\$$   > /tmp/mfc9332cdw_latest_print_info
          cat  /tmp/brmfc9332cdwrc_\$$  >> /tmp/mfc9332cdw_latest_print_info
          rm -f /tmp/brmfc9332cdwrc_\$$

          if [ \$LOGLEVEL -gt 2 ];  then
             if [ \$LOGFILE != "/dev/null" ]; then
               echo ""                                                >>\$LOGFILE
               echo "    ------PostScript Data-------"                >>\$LOGFILE
               cat    \$INPUT_TEMP_PS                                  >>\$LOGFILE
             fi
          fi
      fi
      rm -f  \$INPUT_TEMP_PS

      exit $errorcode
    !ENDOFWFILTER!
    chmod 755 brother_lpdwrapper_mfc9332cdw
    mkdir -p $out/lib/cups/filter
    cp brother_lpdwrapper_mfc9332cdw $out/lib/cups/filter
    '';
}

O script bash de que estou falando é aquele que está configurado cat( installPhaseeu sei, sinto muito, mas na verdade é apenas uma versão modificada do que eles fizeram no script de instalação original do irmão, então essa é a minha desculpa).

Além disso, aqui está a parte relevante do log do CUPS:

Jan 29 15:43:22 kenix-vaio cupsd[11674]: Started filter /nix/store/v0vlk9dni6kn077i3ilfkml4cr8w979b-cups-progs/lib/cups/filter/pdftopdf (PID 11799)
Jan 29 15:43:22 kenix-vaio cupsd[11674]: Started filter /nix/store/v0vlk9dni6kn077i3ilfkml4cr8w979b-cups-progs/lib/cups/filter/pdftops (PID 11800)
Jan 29 15:43:22 kenix-vaio cupsd[11674]: Started filter /nix/store/v0vlk9dni6kn077i3ilfkml4cr8w979b-cups-progs/lib/cups/filter/brother_lpdwrapper_mfc9332cdw (PID 11801)
Jan 29 15:43:22 kenix-vaio cupsd[11674]: Started backend /nix/store/v0vlk9dni6kn077i3ilfkml4cr8w979b-cups-progs/lib/cups/backend/lpd (PID 11802)
Jan 29 15:43:22 kenix-vaio cupsd[11674]: REQUEST localhost - - POST /printers/MFC9332CDW HTTP/1.1 200 127388 Send-Document successful-ok
Jan 29 15:43:22 kenix-vaio cupsd[11674]: execv failed: Exec format error
Jan 29 15:43:22 kenix-vaio cupsd[11674]: PID 11801 (/nix/store/v0vlk9dni6kn077i3ilfkml4cr8w979b-cups-progs/lib/cups/filter/brother_lpdwrapper_mfc9332cdw) stopped with status 108 (Exec format error)