diff --git a/tests/test_check_zkdir.sh b/tests/test_check_zkdir.sh
new file mode 100644
index 0000000..a0302b0
--- /dev/null
+++ b/tests/test_check_zkdir.sh
@@ -0,0 +1,19 @@
+#!/bin/bash
+
+setup() {
+    source ../zk
+}
+
+test_check_zkdir_does_not_error_if_ZKDIR_exists() {
+	export ZKDIR="/"
+
+	assert_status_code 0 check_zkdir
+}
+
+
+test_check_zkdir_errors_if_ZKDIR_does_not_exist() {
+	export ZKDIR="/this/is/a/fake/directory/"
+
+	assert_status_code 1 check_zkdir
+}
+
diff --git a/tests/test_get_command.sh b/tests/test_get_command.sh
index 378da92..1086ed4 100644
--- a/tests/test_get_command.sh
+++ b/tests/test_get_command.sh
@@ -4,6 +4,18 @@ setup() {
 	source ../zk
 }
 
+test_get_command_returns_empty_if_no_input_given() {
+	result="$(get_command "$ZKCOMMANDS" "")"
+
+	assert_equals "" "$result"
+}
+
+test_get_command_returns_empty_if_unrecognized_input_given() {
+	result="$(get_command "$ZKCOMMANDS" "lkjdsaas")"
+
+	assert_equals "" "$result"
+}
+
 test_get_command_returns_list_for_substring() {
 	expected="list"
 
diff --git a/tests/test_main.sh b/tests/test_main.sh
index 7fdf590..387a774 100644
--- a/tests/test_main.sh
+++ b/tests/test_main.sh
@@ -5,6 +5,7 @@ setup() {
 }
 
 test_main_calls_list_when_list_command_passed() {
+	fake check_zkdir test
 	expected="_zk_list"
 	fake get_command 'echo list'
 	fake _zk_list "echo $expected"
@@ -15,6 +16,7 @@ test_main_calls_list_when_list_command_passed() {
 }
 
 test_main_calls_search_when_search_command_passed() {
+	fake check_zkdir test
 	expected="_zk_search"
 	fake get_command 'echo search'
 	fake _zk_search "echo $expected"
@@ -25,6 +27,7 @@ test_main_calls_search_when_search_command_passed() {
 }
 
 test_main_calls_new_when_new_command_passed() {
+	fake check_zkdir test
 	expected="_zk_new"
 	fake get_command 'echo new'
 	fake _zk_new "echo $expected"
@@ -35,6 +38,7 @@ test_main_calls_new_when_new_command_passed() {
 }
 
 test_main_calls_edit_when_edit_command_passed() {
+	fake check_zkdir test
 	expected="_zk_edit"
 	fake get_command 'echo edit'
 	fake _zk_edit "echo $expected"
@@ -43,3 +47,10 @@ test_main_calls_edit_when_edit_command_passed() {
 
 	assert_equals "$expected" "$result"
 }
+
+test_main_errors_if_unrecognized_command_given() {
+	fake check_zkdir test
+	fake get_command echo ""
+
+	assert_status_code 2 main 
+}
diff --git a/zk b/zk
index 392b77b..c9f6df6 100755
--- a/zk
+++ b/zk
@@ -1,15 +1,30 @@
 #!/bin/sh
 
+set -e
+
 ZKDIR="$HOME/.local/share/zk/"
 ZKCOMMANDS='list search new edit'
 
+check_zkdir() {
+	if ! test -d "$ZKDIR"; then
+		echo "zk: $ZKDIR directory does not exist" 1>&2
+		exit 1
+	fi
+}
+
 get_command() {
 	commands="$1"
 	input="$2"
 
+	if test -z "$input"; then
+		echo ""
+		return 0
+	fi
+
 	for c in $commands; do
 		if echo "$c" | grep "^$input" >/dev/null; then
 			echo "$c"
+			return 0
 		fi
 	done
 }
@@ -49,7 +64,15 @@ _zk_edit() {
 }
 
 main() {
+	check_zkdir
+
 	subcommand="$(get_command "$ZKCOMMANDS" "$1")"
+
+	if test -z "$subcommand"; then
+		echo "zk: $1 not recognized" 1>&2
+		exit 2
+	fi
+
 	_zk_"$subcommand"
 }