Fix: read flags from environment variables, as documented

pkg/cmd/cmd.go

@@ -97,16 +97,16 @@ func NewCommand() *cobra.Command {
 		Use:  "kubetrigger",
 		Long: cmdLongHelp,
 		RunE: runCli,
-		PreRunE: func(_ *cobra.Command, _ []string) error {
+		PreRunE: func(c *cobra.Command, _ []string) error {
 			logger.Infof("kube-trigger version=%s", version.Version)
-			return nil
+			if err := applyEnv(c.Flags()); err != nil {
+				return err
+			}
+			return opt.validate()
 		},
 	}
 	c.AddCommand(newVersionCommand())
 	addFlags(opt, c.Flags())
-	if err := opt.validate(); err != nil {
-		panic(err)
-	}
 	return c
 }
 

pkg/cmd/env.go

@@ -0,0 +1,51 @@
+/*
+Copyright 2026 The KubeVela Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package cmd
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"strings"
+
+	"github.com/spf13/pflag"
+)
+
+// applyEnv sets each flag not given on the command line from its environment
+// variable, so the order is command line, then environment, then default.
+func applyEnv(fs *pflag.FlagSet) error {
+	var errs []error
+	fs.VisitAll(func(f *pflag.Flag) {
+		if f.Changed || f.Name == "help" {
+			return
+		}
+		name := envName(f.Name)
+		v, ok := os.LookupEnv(name)
+		if !ok {
+			return
+		}
+		if err := fs.Set(f.Name, v); err != nil {
+			errs = append(errs, fmt.Errorf("$%s: %w", name, err))
+		}
+	})
+	return errors.Join(errs...)
+}
+
+// envName is a flag's environment variable: its name in capitals, with - as _.
+func envName(flag string) string {
+	return strings.ToUpper(strings.ReplaceAll(flag, "-", "_"))
+}

pkg/cmd/env_test.go

@@ -0,0 +1,79 @@
+/*
+Copyright 2026 The KubeVela Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package cmd
+
+import (
+	"testing"
+	"time"
+
+	"github.com/spf13/pflag"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// parse reads args into a fresh option, then applies the environment.
+func parse(t *testing.T, args ...string) (*option, error) {
+	o := newOption()
+	fs := pflag.NewFlagSet("kubetrigger", pflag.ContinueOnError)
+	addFlags(o, fs)
+	require.NoError(t, fs.Parse(args))
+	return o, applyEnv(fs)
+}
+
+func TestEnvSetsAFlagNotGiven(t *testing.T) {
+	t.Setenv("MAX_RETRY", "9")
+	o, err := parse(t)
+	require.NoError(t, err)
+	assert.Equal(t, 9, o.MaxRetry)
+}
+
+func TestFlagBeatsEnv(t *testing.T) {
+	t.Setenv("MAX_RETRY", "9")
+	o, err := parse(t, "--max-retry=3")
+	require.NoError(t, err)
+	assert.Equal(t, 3, o.MaxRetry)
+}
+
+func TestDefaultWithoutEither(t *testing.T) {
+	o, err := parse(t)
+	require.NoError(t, err)
+	assert.Equal(t, defaultMaxRetry, o.MaxRetry)
+}
+
+func TestEnvNames(t *testing.T) {
+	t.Setenv("PER_WORKER_QPS", "7")
+	t.Setenv("LEADER_ELECT", "true")
+	t.Setenv("LEADER_ELECTION_LEASE_DURATION", "42s")
+	o, err := parse(t)
+	require.NoError(t, err)
+	assert.Equal(t, 7, o.PerWorkerQPS)
+	assert.True(t, enableLeaderElection)
+	assert.Equal(t, 42*time.Second, leaseDuration)
+}
+
+func TestBadEnvValueNamesItsVariable(t *testing.T) {
+	t.Setenv("MAX_RETRY", "lots")
+	_, err := parse(t)
+	assert.ErrorContains(t, err, "MAX_RETRY")
+}
+
+func TestValidationSeesFlagsAndEnv(t *testing.T) {
+	t.Setenv("WORKERS", "0")
+	c := NewCommand()
+	require.NoError(t, c.ParseFlags(nil))
+	assert.ErrorContains(t, c.PreRunE(c, nil), "workers")
+}