improve test script for emulation station

launch_es.sh

@@ -1,5 +1,21 @@
 export NIXPKGS_ALLOW_UNFREE=1
 
-RESULT=$(nix-build -E 'import ((import ./npins).nixpkgs + "/nixos")'  -A config.retronix.emulationstation.cli -I nixos-config=configuration.nix --no-out-link $@)
+# get script dir
+#
+SOURCE=${BASH_SOURCE[0]}
+while [ -L "$SOURCE" ]; do # resolve $SOURCE until the file is no longer a symlink
+  DIR=$( cd -P "$( dirname "$SOURCE" )" >/dev/null 2>&1 && pwd )
+  SOURCE=$(readlink "$SOURCE")
+  [[ $SOURCE != /* ]] && SOURCE=$DIR/$SOURCE # if $SOURCE was a relative symlink, we need to resolve it relative to the path where the symlink file was located
+done
+DIR=$( cd -P "$( dirname "$SOURCE" )" >/dev/null 2>&1 && pwd )
+
+pushd "$DIR" || exit 1
+
+RESULT=$(nix-build -E 'import ((import ./npins).nixpkgs + "/nixos")'  -A config.retronix.emulationstation.cli -I nixos-config=configuration.nix --no-out-link $@) || popd || exit 1
+
+popd || exit 1
+
+echo -e "Running: $RESULT\n"
 
 $RESULT