nixpkgs should be the one provided in the command line

run.sh

@@ -1,11 +1,13 @@
 #!/bin/sh
 
 NIXPKGS='<nixpkgs/maintainers/scripts/find-tarballs.nix>'
+NIX='<nixpkgs>'
 
 while getopts "f:" arg; do
   case ${arg} in
     f)
       NIXPKGS="${OPTARG}/maintainers/scripts/find-tarballs.nix"
+      NIX="${OPTARG}"
       shift
       shift
       ;;
@@ -24,4 +26,4 @@ fi
 
 echo "DOWNLOADING SOURCES TO BUILD $@" > /dev/stderr
 mkdir -p "distfiles"
-nix-instantiate --json --eval --strict "${NIXPKGS}" --arg expr "with import <nixpkgs>{}; [$*]" # | ./mirror.pl
+nix-instantiate --json --eval --strict "${NIXPKGS}" --arg expr "with import ${NIX}{}; [$*]" # | ./mirror.pl