diff --git a/flupdt/flake_build.py b/flupdt/flake_build.py
index 3821396..1a57d55 100644
--- a/flupdt/flake_build.py
+++ b/flupdt/flake_build.py
@@ -11,6 +11,7 @@ from flupdt.common import bash_wrapper
 drv_re = re.compile(r".*(/nix/store/.*\.drv).*")
 
 OUTPUT_DIR = mkdtemp(prefix="flupdt-outputs-")
+logger = logging.getLogger(__name__)
 
 
 def build_output(path: str, output: str) -> str | None:
@@ -20,16 +21,16 @@ def build_output(path: str, output: str) -> str | None:
     :param output: flake output to be built
     :returns the .drv path on success or None on failure
     """
-    logging.info(f"build {output}")
-    logging.debug(f"outputting to {OUTPUT_DIR}/{output}.nixoutput")
+    logger.info(f"build {output}")
+    logger.debug(f"outputting to {OUTPUT_DIR}/{output}.nixoutput")
     out = bash_wrapper(f"nix build {path}#{output} -o {OUTPUT_DIR}/{output}.nixoutput")
-    logging.debug("output")
-    logging.debug(out[0])
-    logging.debug("error")
-    logging.debug(out[1])
-    logging.debug("statuscode")
-    logging.debug(out[2])
+    logger.debug("output")
+    logger.debug(out[0])
+    logger.debug("error")
+    logger.debug(out[1])
+    logger.debug("statuscode")
+    logger.debug(out[2])
     if out[2] != 0:
-        logging.warning(f"output {output} did not build correctly")
+        logger.warning(f"output {output} did not build correctly")
         return None
     return ""
diff --git a/flupdt/flake_diff.py b/flupdt/flake_diff.py
index fa16c80..52d5de2 100644
--- a/flupdt/flake_diff.py
+++ b/flupdt/flake_diff.py
@@ -5,6 +5,8 @@ import shutil
 
 from flupdt.common import bash_wrapper
 
+logger = logging.getLogger(__name__)
+
 
 def compare_derivations(
     path_to_flake: str, path_to_pre_drv: str, path_to_post_drv: str, *, soft_failure: bool = True
@@ -24,10 +26,10 @@ def compare_derivations(
     )
 
     if returncode != 0:
-        log_func = logging.error
+        log_func = logger.error
         if soft_failure:
-            log_func = logging.warning
-        logging.warning(f"diff failed for {path_to_pre_drv} and {path_to_post_drv}")
+            log_func = logger.warning
+        logger.warning(f"diff failed for {path_to_pre_drv} and {path_to_post_drv}")
         log_func(stderr)
 
     return stdout
diff --git a/flupdt/flake_eval.py b/flupdt/flake_eval.py
index 99caba9..e88d03c 100644
--- a/flupdt/flake_eval.py
+++ b/flupdt/flake_eval.py
@@ -9,6 +9,8 @@ from flupdt.common import bash_wrapper
 
 drv_re = re.compile(r".*(/nix/store/.*\.drv).*")
 
+logger = logging.getLogger(__name__)
+
 
 def evaluate_output(path: str, output: str) -> str | None:
     """Evaluates a given output in a flake.
@@ -18,19 +20,19 @@ def evaluate_output(path: str, output: str) -> str | None:
     :returns the .drv path on success or None on failure
     :raises RuntimeError: evaluation succeeds but no derivation is found
     """
-    logging.info(f"evaluating {output}")
+    logger.info(f"evaluating {output}")
     out = bash_wrapper(f"nix eval {path}#{output}")
-    logging.debug(out[0])
-    logging.debug(out[1])
-    logging.debug(out[2])
+    logger.debug(out[0])
+    logger.debug(out[1])
+    logger.debug(out[2])
     if out[2] != 0:
-        logging.warning(f"output {output} did not evaluate correctly")
+        logger.warning(f"output {output} did not evaluate correctly")
         return None
     drv_match = drv_re.match(out[0])
     if drv_match is None:
         out_msg = "derivation succeeded but output derivation does not contain a derivation"
         raise RuntimeError(out_msg)
     drv = drv_match.group(1)
-    logging.debug(f"derivation evaluated to {drv}")
+    logger.debug(f"derivation evaluated to {drv}")
 
     return drv
diff --git a/flupdt/flake_show.py b/flupdt/flake_show.py
index aea4170..9704f3c 100644
--- a/flupdt/flake_show.py
+++ b/flupdt/flake_show.py
@@ -12,6 +12,7 @@ output_regexes = [
     re.compile(r"checking derivation (.*)..."),
     re.compile(r"checking NixOS configuration \'(nixosConfigurations.*)\'\.\.\."),
 ]
+logger = logging.getLogger(__name__)
 
 
 def traverse_json_base(json_dict: dict[str, typing.Any], path: list[str]) -> list[str]:
@@ -54,7 +55,7 @@ def get_derivations_from_check(nix_path: str, path_to_flake: str) -> list[str]:
     """
     flake_check = bash_wrapper(f"{nix_path} flake check --verbose --keep-going", path=path_to_flake)
     if flake_check[2] != 0:
-        logging.warning(
+        logger.warning(
             "nix flake check returned non-zero exit code, collecting all available outputs"
         )
     error_out = flake_check[1].split("\n")
@@ -62,10 +63,10 @@ def get_derivations_from_check(nix_path: str, path_to_flake: str) -> list[str]:
     derivations = []
     for output in possible_outputs:
         for r in output_regexes:
-            logging.debug(f"{output} {r.pattern}")
+            logger.debug(f"{output} {r.pattern}")
             match = r.match(output)
             if match is not None:
-                logging.debug(match.groups())
+                logger.debug(match.groups())
                 derivations += [match.groups()[0]]
     return derivations
 
@@ -84,8 +85,8 @@ def get_derivations(path_to_flake: str) -> list[str]:
         raise RuntimeError(status_msg)
     flake_show = bash_wrapper(f"{nix_path} flake show --json", path=path_to_flake)
     if flake_show[2] != 0:
-        logging.error("flake show returned non-zero exit code")
-        logging.warning("falling back to full evaluation via nix flake check")
+        logger.error("flake show returned non-zero exit code")
+        logger.warning("falling back to full evaluation via nix flake check")
         derivations = get_derivations_from_check(nix_path, path_to_flake)
     else:
         flake_show_json = json.loads(flake_show[0])
diff --git a/flupdt/main.py b/flupdt/main.py
index edff707..151f4de 100755
--- a/flupdt/main.py
+++ b/flupdt/main.py
@@ -4,6 +4,7 @@
 
 import logging
 import os
+import sys
 from argparse import Namespace
 from pathlib import Path
 
@@ -14,6 +15,8 @@ from flupdt.flake_diff import compare_derivations
 from flupdt.flake_eval import evaluate_output
 from flupdt.flake_show import get_derivations
 
+logger = logging.getLogger(__name__)
+
 
 def batch_eval(args: Namespace, flake_path: str, derivations: list[str]) -> None:
     """Bulk run evaluations or builds on a derivation set.
@@ -28,12 +31,14 @@ def batch_eval(args: Namespace, flake_path: str, derivations: list[str]) -> None
         if args.evaluate:
             drv_map[d] = evaluate_output(flake_path, d)
         if args.build:
-            build_output(flake_path, d)
+            drv_map[d] = build_output(flake_path, d)
     if args.json:
         with Path.open(args.json, "w+") as f:
             from json import dump
 
             dump(drv_map, f)
+    if any(x is None for x in drv_map.values()):
+        sys.exit(1)
 
 
 def compare_drvs(args: Namespace) -> None:
@@ -52,8 +57,8 @@ def compare_drvs(args: Namespace) -> None:
         pre_json_dict = load(pre)
         post_json_dict = load(post)
 
-    logging.debug(f"pre-snapshot derivations: {pre_json_dict}")
-    logging.debug(f"post-snapshot derivations: {post_json_dict}")
+    logger.debug(f"pre-snapshot derivations: {pre_json_dict}")
+    logger.debug(f"post-snapshot derivations: {post_json_dict}")
 
     pre_json_keys = set(pre_json_dict.keys())
     post_json_keys = set(post_json_dict.keys())
@@ -64,11 +69,11 @@ def compare_drvs(args: Namespace) -> None:
     missing_pre_keys = post_json_keys.difference(common_keys_to_eval)
 
     if missing_pre_keys:
-        logging.warning(f"Following outputs are missing from pre-snapshot: {missing_pre_keys}")
+        logger.warning(f"Following outputs are missing from pre-snapshot: {missing_pre_keys}")
     if missing_post_keys:
-        logging.warning(f"Following outputs are missing from post-snapshot: {missing_post_keys}")
+        logger.warning(f"Following outputs are missing from post-snapshot: {missing_post_keys}")
 
-    logging.info(f"Evaluating the following outputs for differences: {common_keys_to_eval}")
+    logger.info(f"Evaluating the following outputs for differences: {common_keys_to_eval}")
 
     out_file: str = os.devnull
     if args.compare_output_to_file:
@@ -97,11 +102,11 @@ def build_or_eval(args: Namespace) -> None:
         lambda s: s.startswith("hydraJobs"), get_derivations(flake_path)
     )
     derivations, hydra_jobs = list(derivations), list(hydra_jobs)
-    logging.info(f"derivations: {list(derivations)}")
+    logger.info(f"derivations: {list(derivations)}")
     batch_eval(args, flake_path, derivations)
 
     if not args.keep_hydra:
-        logging.info("--keep-hydra flag is not specified, removing Hydra jobs")
+        logger.info("--keep-hydra flag is not specified, removing Hydra jobs")
     else:
         batch_eval(args, flake_path, hydra_jobs)
 
@@ -112,7 +117,7 @@ def main() -> None:
     :returns: None
 
     """
-    configure_logger("DEBUG")
+    configure_logger("INFO")
     args = parse_inputs()
     if args.compare_drvs:
         compare_drvs(args)