diff --git a/src/alas.janet b/src/alas.janet
index db33079..6ded593 100644
--- a/src/alas.janet
+++ b/src/alas.janet
@@ -5,13 +5,11 @@
 
 (import ./commands :prefix "")
 
+(import ./errors)
 (import ./file_repository)
 (import ./plan/parser :as plan_parser)
 (import ./plan/serializer :as plan_serializer)
 
-(defn- print-errors [errors]
-  (each error errors (print (string error "."))))
-
 # Keep commands sorted alphabetically.
 (def argparse-params
   ["A command line utility for planning your days"
@@ -42,19 +40,21 @@
   (def load-file-result (file_repository/load file-path))
   (def errors (load-file-result :errors))
   (if errors
-    (print-errors errors)
+    (errors/print-errors errors (errors/exit-status-codes :file-error))
     (let [plan-string (load-file-result :text)
           parse-result (plan_parser/parse plan-string)
           parse-errors (parse-result :errors)
           plan (parse-result :plan)]
       (if parse-errors
-        (print-errors parse-errors)
-        (let [serialize-empty-inbox (plan_parser/serialize-empty-inbox? plan-string)
-              new-plan (run-commands plan file-path arguments)
-              new-plan-string (plan_serializer/serialize
+        (errors/print-errors parse-errors (errors/exit-status-codes :parse-error))
+        (let [{:plan new-plan :errors run-errors} (run-commands plan file-path arguments)]
+          (if (empty? run-errors)
+            (let [serialize-empty-inbox (plan_parser/serialize-empty-inbox? plan-string)
+                  new-plan-string (plan_serializer/serialize
                                 new-plan
                                 {:serialize-empty-inbox serialize-empty-inbox})]
-          (file_repository/save new-plan-string file-path))))))
+              (file_repository/save new-plan-string file-path))
+            (errors/print-errors run-errors (errors/exit-status-codes :command-error))))))))
 
 (defn- run-with-arguments [arguments]
   (def file-path (arguments :default))
@@ -62,7 +62,8 @@
     (run-with-file-path arguments file-path)
     (if (arguments "version")
       (print-version)
-      (print "Plan file path missing."))))
+      (errors/print-errors ["Plan file path is missing"]
+                           (errors/exit-status-codes :plan-path-missing)))))
 
 ## —————————————————————————————————————————————————————————————————————————————————————————————————
 ## Public Interface
diff --git a/src/commands.janet b/src/commands.janet
index dbafa10..69c9ecc 100644
--- a/src/commands.janet
+++ b/src/commands.janet
@@ -12,6 +12,7 @@
 (import ./commands/stats)
 
 (import ./date :as d)
+(import ./errors)
 (import ./schedule_parser)
 
 # backup command needs to be first
@@ -27,10 +28,6 @@
                schedule_tasks/build-command
                stats/build-command])
 
-(defn- print-errors [errors]
-  (loop [error :in errors]
-    (print error)))
-
 ## —————————————————————————————————————————————————————————————————————————————————————————————————
 ## Public Interface
 
@@ -49,13 +46,12 @@
 (defn run-commands [plan file-path arguments]
   (def commands (build-commands arguments file-path))
   (def errors (filter identity (flatten (map (fn [c] (c :errors)) commands))))
-  (if (any? errors)
-    (do
-      (print-errors errors)
-      plan)
-    (reduce (fn [new-plan command-and-arguments]
-              (def command (first (command-and-arguments :command)))
-              (def arguments (drop 1 (command-and-arguments :command)))
-              (apply command new-plan arguments))
-            plan
-            commands)))
+  (var new-plan plan)
+  (if (empty? errors)
+    (set new-plan (reduce (fn [new-plan command-and-arguments]
+                            (def command (first (command-and-arguments :command)))
+                            (def arguments (drop 1 (command-and-arguments :command)))
+                            (apply command new-plan arguments))
+                         plan
+                         commands)))
+  {:plan new-plan :errors errors})
diff --git a/src/commands/list_contacts.janet b/src/commands/list_contacts.janet
index 121ede2..eb7a51a 100644
--- a/src/commands/list_contacts.janet
+++ b/src/commands/list_contacts.janet
@@ -3,6 +3,7 @@
 
 (import ../utils :prefix "")
 (import ../date :as d)
+(import ../errors)
 (import ../contact/repository :as contacts_repository)
 
 (defn- to-csv-line [contact]
@@ -35,6 +36,6 @@
     (let [load-result (contacts_repository/load-contacts argument)
           errors (load-result :errors)]
       (if errors
-        {:errors (format-command-errors "--list-contacts" errors)}
+        {:errors (errors/format-command-errors "--list-contacts" errors)}
         {:command [print-contacts (load-result :contacts)]}))
     {}))
diff --git a/src/commands/schedule_contacts.janet b/src/commands/schedule_contacts.janet
index 6ef4b73..9f3f1eb 100644
--- a/src/commands/schedule_contacts.janet
+++ b/src/commands/schedule_contacts.janet
@@ -1,6 +1,7 @@
 ### ————————————————————————————————————————————————————————————————————————————————————————————————
 ### This module implements a command for scheduling contacts for today in a plan.
 
+(import ../errors)
 (import ../utils :prefix "")
 
 (import ../contact)
@@ -69,6 +70,6 @@
           errors (load-result :errors)
           contacts (load-result :contacts)]
       (if errors
-        {:errors (format-command-errors "--schedule-contacts" errors)}
+        {:errors (errors/format-command-errors "--schedule-contacts" errors)}
         {:command [schedule-contacts contacts (date/today)]}))
     {}))
diff --git a/src/commands/schedule_tasks.janet b/src/commands/schedule_tasks.janet
index e384fc2..0f63c20 100644
--- a/src/commands/schedule_tasks.janet
+++ b/src/commands/schedule_tasks.janet
@@ -8,6 +8,7 @@
 (import ../plan)
 (import ../task)
 
+(import ../errors)
 (import ../file_repository)
 (import ../schedule_parser)
 
@@ -84,10 +85,10 @@
     (let [load-file-result (file_repository/load argument)
           errors (load-file-result :errors)]
       (if errors
-        {:errors (format-command-errors command errors)}
+        {:errors (errors/format-command-errors command errors)}
         (let [parse-result (schedule_parser/parse (load-file-result :text))
               errors (parse-result :errors)]
           (if errors
-            {:errors (format-command-errors command errors)}
+            {:errors (errors/format-command-errors command errors)}
             {:command [schedule-tasks (parse-result :tasks) (date/today)]}))))
     {}))
diff --git a/src/errors.janet b/src/errors.janet
new file mode 100644
index 0000000..781249d
--- /dev/null
+++ b/src/errors.janet
@@ -0,0 +1,19 @@
+### ————————————————————————————————————————————————————————————————————————————————————————————————
+### Errors.
+
+## —————————————————————————————————————————————————————————————————————————————————————————————————
+## Public Interface
+
+(def exit-status-codes
+  {:error 1
+   :plan-path-missing 2
+   :file-error 3
+   :parse-error 4
+   :command-error 5})
+
+(defn format-command-errors [command errors]
+  (map (fn [error] (string command " " (string/ascii-lower error))) errors))
+
+(defn print-errors [errors exit-status-code]
+  (each error errors (print (string error ".")))
+  (os/exit exit-status-code))
diff --git a/src/utils.janet b/src/utils.janet
index 873a099..b4b5ff1 100644
--- a/src/utils.janet
+++ b/src/utils.janet
@@ -13,6 +13,3 @@
   (if (string/has-suffix? "/" path)
     (string/trimr path "/")
     path))
-
-(defn format-command-errors [command errors]
-  (map (fn [error] (string command " " (string/ascii-lower error) ".")) errors))
diff --git a/test/commands/list_contacts_test.janet b/test/commands/list_contacts_test.janet
index 27deb40..ee531c9 100644
--- a/test/commands/list_contacts_test.janet
+++ b/test/commands/list_contacts_test.janet
@@ -32,4 +32,4 @@
 (deftest "when the directory doesn't exist"
   (def arguments {"list-contacts" "test/missing-directory"})
   (def result (build-command arguments))
-  (test (first (result :errors)) "--list-contacts directory does not exist."))
+  (test (first (result :errors)) "--list-contacts directory does not exist"))
diff --git a/test/commands/schedule_contacts_test.janet b/test/commands/schedule_contacts_test.janet
index 5516b8d..d4008c4 100644
--- a/test/commands/schedule_contacts_test.janet
+++ b/test/commands/schedule_contacts_test.janet
@@ -127,4 +127,4 @@
   (def arguments {"schedule-contacts" "test/examples/people"})
   (def result (build-command arguments))
   (test (nil? (result :command)) true)
-  (test (first (result :errors)) "--schedule-contacts directory does not exist."))
+  (test (first (result :errors)) "--schedule-contacts directory does not exist"))
diff --git a/test/commands/schedule_tasks_test.janet b/test/commands/schedule_tasks_test.janet
index b637e7f..f7bf229 100644
--- a/test/commands/schedule_tasks_test.janet
+++ b/test/commands/schedule_tasks_test.janet
@@ -225,16 +225,16 @@
   (def arguments {"schedule-tasks" "test/examples/missing-schedule.md"})
   (def result (build-command arguments))
   (test (nil? (result :command)) true)
-  (test (first (result :errors)) "--schedule-tasks file does not exist."))
+  (test (first (result :errors)) "--schedule-tasks file does not exist"))
 
 (deftest "returns an error when the schedule cannot be parsed"
   (def arguments {"schedule-tasks" "test/examples/unparsable-schedule.md"})
   (def result (build-command arguments))
   (test (nil? (result :command)) true)
-  (test (first (result :errors)) "--schedule-tasks schedule can not be parsed."))
+  (test (first (result :errors)) "--schedule-tasks schedule can not be parsed"))
 
 (deftest "returns an error when the schedule is empty"
   (def arguments {"schedule-tasks" "test/examples/empty-schedule.md"})
   (def result (build-command arguments))
   (test (nil? (result :command)) true)
-  (test (first (result :errors)) "--schedule-tasks schedule is empty."))
+  (test (first (result :errors)) "--schedule-tasks schedule is empty"))
diff --git a/test/commands_test.janet b/test/commands_test.janet
index 72ee8ad..83a06ca 100644
--- a/test/commands_test.janet
+++ b/test/commands_test.janet
@@ -54,8 +54,9 @@
                       (day/build-day (d/date 2020 8 2) @[]
                                      @[(task/build-task "Buy milk" true)])]))
   (def arguments {"skip-backup" true "remove-empty-days" true "insert-days" "3"})
-  (def new-plan (run-commands plan file-path arguments))
+  (def {:plan new-plan :errors errors} (run-commands plan file-path arguments))
   (def days (new-plan :days))
+  (test (empty? errors) true)
   (test (length days) 4)
   (test (= (d/+days today 2) ((days 0) :date)) true)
   (test (= (d/+days today 1) ((days 1) :date)) true)
@@ -70,9 +71,10 @@
                       (day/build-day (d/date 2020 8 2) @[]
                                      @[(task/build-task "Buy milk" true)])]))
   (def arguments {"skip-backup" true "remove-empty-days" true "insert-days" "three"})
-  (def new-plan (run-commands plan file-path arguments))
+  (def {:plan new-plan :errors errors} (run-commands plan file-path arguments))
   (def days (new-plan :days))
   (test (length days) 3)
   (test (= today ((days 0) :date)) true)
   (test (= (d/date 2020 8 4) ((days 1) :date)) true)
-  (test (= (d/date 2020 8 2) ((days 2) :date)) true))
+  (test (= (d/date 2020 8 2) ((days 2) :date)) true)
+  (test (= (first errors) "--insert-days argument is not a number.") true))
diff --git a/test/examples/my-plan.md b/test/examples/my-plan.md
deleted file mode 100644
index f22af81..0000000
--- a/test/examples/my-plan.md
+++ /dev/null
@@ -1,3 +0,0 @@
-# My Plan
-
-## 2022-05-12
diff --git a/test/examples/todo-2022-02-10.md b/test/examples/todo-2022-02-10.md
deleted file mode 100644
index 713d15e..0000000
--- a/test/examples/todo-2022-02-10.md
+++ /dev/null
@@ -1,13 +0,0 @@
-# Main TODO
-
-## Inbox
-
-## 2020-08-01, Saturday
-
-- [ ] Develop photos for the grandmother
-- [X] Pay bills
-
-## 2020-07-31, Friday
-
-- [X] Review open pull requests
-- [X] Fix flaky test