7 files changed, 86 insertions, 2 deletions
diff --git a/internal/cmd/config.go b/internal/cmd/config.go
index 1fae0346..7f071417 100644
--- a/internal/cmd/config.go
+++ b/internal/cmd/config.go
@@ -160,6 +160,11 @@ func cobraConfig(cmd *cobra.Command, args []string) (cfg *config.Config, err err
 		return nil, err
 	}
 
+	cfg.MissingKey, err = getString(cmd, "missing-key")
+	if err != nil {
+		return nil, err
+	}
+
 	ds, err := getStringSlice(cmd, "datasource")
 	if err != nil {
 		return nil, err
diff --git a/internal/cmd/main.go b/internal/cmd/main.go
index 7533f855..3cce83e2 100644
--- a/internal/cmd/main.go
+++ b/internal/cmd/main.go
@@ -156,6 +156,8 @@ func InitFlags(command *cobra.Command) {
 	command.Flags().String("left-delim", ldDefault, "override the default left-`delimiter` [$GOMPLATE_LEFT_DELIM]")
 	command.Flags().String("right-delim", rdDefault, "override the default right-`delimiter` [$GOMPLATE_RIGHT_DELIM]")
 
+	command.Flags().String("missing-key", "error", "Control the behavior during execution if a map is indexed with a key that is not present in the map. error (default) - return an error, zero - fallback to zero value, default/invalid - print <no value>")
+
 	command.Flags().Bool("experimental", false, "enable experimental features [$GOMPLATE_EXPERIMENTAL]")
 
 	command.Flags().BoolP("verbose", "V", false, "output extra information about what gomplate is doing")
diff --git a/internal/config/configfile.go b/internal/config/configfile.go
index 712d7310..1ed266b3 100644
--- a/internal/config/configfile.go
+++ b/internal/config/configfile.go
@@ -13,6 +13,8 @@ import (
 	"strings"
 	"time"
 
+	"golang.org/x/exp/slices"
+
 	"github.com/hairyhenderson/gomplate/v4/internal/datafs"
 	"github.com/hairyhenderson/gomplate/v4/internal/iohelpers"
 	"github.com/hairyhenderson/yaml"
@@ -60,6 +62,8 @@ type Config struct {
 	LDelim string `yaml:"leftDelim,omitempty"`
 	RDelim string `yaml:"rightDelim,omitempty"`
 
+	MissingKey string `yaml:"missingKey,omitempty"`
+
 	PostExec []string `yaml:"postExec,omitempty,flow"`
 
 	PluginTimeout time.Duration `yaml:"pluginTimeout,omitempty"`
@@ -465,6 +469,13 @@ func (c Config) Validate() (err error) {
 		}
 	}
 
+	if err == nil {
+		missingKeyValues := []string{"", "error", "zero", "default", "invalid"}
+		if !slices.Contains(missingKeyValues, c.MissingKey) {
+			err = fmt.Errorf("not allowed value for the 'missing-key' flag: %s. Allowed values: %s", c.MissingKey, strings.Join(missingKeyValues, ","))
+		}
+	}
+
 	return err
 }
 
@@ -533,6 +544,9 @@ func (c *Config) ApplyDefaults() {
 	if c.RDelim == "" {
 		c.RDelim = "}}"
 	}
+	if c.MissingKey == "" {
+		c.MissingKey = "error"
+	}
 
 	if c.ExecPipe {
 		pipe := &bytes.Buffer{}
diff --git a/internal/config/configfile_test.go b/internal/config/configfile_test.go
index e99fc8b4..449c379b 100644
--- a/internal/config/configfile_test.go
+++ b/internal/config/configfile_test.go
@@ -539,6 +539,7 @@ inputFiles: ['-']
 outputFiles: ['-']
 leftDelim: '{{'
 rightDelim: '}}'
+missingKey: error
 pluginTimeout: 5s
 `
 		assert.Equal(t, expected, c.String())
diff --git a/internal/tests/integration/config_test.go b/internal/tests/integration/config_test.go
index d56616ae..00ab4f89 100644
--- a/internal/tests/integration/config_test.go
+++ b/internal/tests/integration/config_test.go
@@ -275,3 +275,23 @@ templates:
 	o, e, err := cmd(t).withDir(tmpDir.Path()).run()
 	assertSuccess(t, o, e, err, "12345")
 }
+
+func TestConfig_MissingKeyDefault(t *testing.T) {
+	tmpDir := setupConfigTest(t)
+	writeConfig(t, tmpDir, `inputFiles: [in]
+missingKey: default
+`)
+	writeFile(t, tmpDir, "in", `{{ .name }}`)
+
+	o, e, err := cmd(t).withDir(tmpDir.Path()).run()
+	assertSuccess(t, o, e, err, `<no value>`)
+}
+
+func TestConfig_MissingKeyNotDefined(t *testing.T) {
+	tmpDir := setupConfigTest(t)
+	writeConfig(t, tmpDir, `inputFiles: [in]`)
+	writeFile(t, tmpDir, "in", `{{ .name }}`)
+
+	o, e, err := cmd(t).withDir(tmpDir.Path()).run()
+	assertFailed(t, o, e, err, `map has no entry for key \"name\"`)
+}
diff --git a/internal/tests/integration/integration_test.go b/internal/tests/integration/integration_test.go
index bc79862a..a57d8d0b 100644
--- a/internal/tests/integration/integration_test.go
+++ b/internal/tests/integration/integration_test.go
@@ -25,13 +25,22 @@ import (
 const isWindows = runtime.GOOS == "windows"
 
 // a convenience...
-func inOutTest(t *testing.T, i, o string) {
+func inOutTest(t *testing.T, i, o string, args ...string) {
 	t.Helper()
 
-	stdout, stderr, err := cmd(t, "-i", i).run()
+	args = append(args, "-i", i)
+	stdout, stderr, err := cmd(t, args...).run()
 	assertSuccess(t, stdout, stderr, err, o)
 }
 
+func inOutContainsError(t *testing.T, i, e string, args ...string) {
+	t.Helper()
+
+	args = append(args, "-i", i)
+	stdout, stderr, err := cmd(t, args...).run()
+	assertFailed(t, stdout, stderr, err, e)
+}
+
 func inOutTestExperimental(t *testing.T, i, o string) {
 	t.Helper()
 
@@ -56,6 +65,14 @@ func assertSuccess(t *testing.T, o, e string, err error, expected string) {
 	require.NoError(t, err)
 }
 
+func assertFailed(t *testing.T, o, e string, err error, expected string) {
+	t.Helper()
+
+	assert.Contains(t, e, expected)
+	assert.Equal(t, "", o)
+	require.Error(t, err)
+}
+
 // mirrorHandler - reflects back the HTTP headers from the request
 func mirrorHandler(w http.ResponseWriter, r *http.Request) {
 	type Req struct {
diff --git a/internal/tests/integration/missing_key_test.go b/internal/tests/integration/missing_key_test.go
new file mode 100644
index 00000000..076ff236
--- /dev/null
+++ b/internal/tests/integration/missing_key_test.go
@@ -0,0 +1,25 @@
+package integration
+
+import (
+	"testing"
+)
+
+func TestMissingKey_Default(t *testing.T) {
+	inOutTest(t, `{{ .name }}`, "<no value>", "--missing-key", "default")
+}
+
+func TestMissingKey_Zero(t *testing.T) {
+	inOutTest(t, `{{ .name }}`, "<no value>", "--missing-key", "zero")
+}
+
+func TestMissingKey_Fallback(t *testing.T) {
+	inOutTest(t, `{{ .name | default "Alex" }}`, "Alex", "--missing-key", "default")
+}
+
+func TestMissingKey_NotSpecified(t *testing.T) {
+	inOutContainsError(t, `{{ .name | default "Alex" }}`, `map has no entry for key \"name\"`)
+}
+
+func TestMissingKey_Error(t *testing.T) {
+	inOutContainsError(t, `{{ .name | default "Alex" }}`, `map has no entry for key \"name\"`, "--missing-key", "error")
+}