support writing run output to files

so that it isn't necessary to wrap in bash to redirect to a file

cmd/config/cmd/cat.go

@@ -5,9 +5,11 @@ package cmd
 
 import (
 	"fmt"
+	"os"
 
 	"github.com/spf13/cobra"
 	"sigs.k8s.io/kustomize/cmd/config/cmddocs/commands"
+	"sigs.k8s.io/kustomize/kyaml/errors"
 	"sigs.k8s.io/kustomize/kyaml/kio"
 	"sigs.k8s.io/kustomize/kyaml/kio/filters"
 	"sigs.k8s.io/kustomize/kyaml/yaml"
@@ -45,6 +47,8 @@ func GetCatRunner(name string) *CatRunner {
 		"if true, include local-config in the output.")
 	c.Flags().BoolVar(&r.ExcludeNonLocal, "exclude-non-local", false,
 		"if true, exclude non-local-config in the output.")
+	c.Flags().StringVar(&r.OutputDest, "dest", "",
+		"if specified, write output to a file rather than stdout")
 	r.Command = c
 	return r
 }
@@ -61,6 +65,7 @@ type CatRunner struct {
 	WrapKind           string
 	WrapApiVersion     string
 	FunctionConfig     string
+	OutputDest         string
 	Styles             []string
 	StripComments      bool
 	IncludeLocal       bool
@@ -106,9 +111,19 @@ func (r *CatRunner) runE(c *cobra.Command, args []string) error {
 		fltr = append(fltr, filters.StripCommentsFilter{})
 	}
 
+	var out = c.OutOrStdout()
+	if r.OutputDest != "" {
+		o, err := os.Create(r.OutputDest)
+		if err != nil {
+			return handleError(c, errors.Wrap(err))
+		}
+		defer o.Close()
+		out = o
+	}
+
 	var outputs []kio.Writer
 	outputs = append(outputs, kio.ByteWriter{
-		Writer:                c.OutOrStdout(),
+		Writer:                out,
 		KeepReaderAnnotations: r.KeepAnnotations,
 		WrappingKind:          r.WrapKind,
 		WrappingApiVersion:    r.WrapApiVersion,

cmd/config/cmd/cat_test.go

@@ -325,3 +325,246 @@ spec:
 		return
 	}
 }
+
+func TestCmd_outputTruncateFile(t *testing.T) {
+	d, err := ioutil.TempDir("", "kustomize-cat-test")
+	if !assert.NoError(t, err) {
+		return
+	}
+	defer os.RemoveAll(d)
+
+	err = ioutil.WriteFile(filepath.Join(d, "f1.yaml"), []byte(`
+kind: Deployment
+metadata:
+  labels:
+    app: nginx2
+  name: foo
+  annotations:
+    app: nginx2
+spec:
+  replicas: 1
+---
+kind: Service
+metadata:
+  name: foo
+  annotations:
+    app: nginx
+spec:
+  selector:
+    app: nginx
+`), 0600)
+	if !assert.NoError(t, err) {
+		return
+	}
+	err = ioutil.WriteFile(filepath.Join(d, "f2.yaml"), []byte(`
+apiVersion: v1
+kind: Abstraction
+metadata:
+  name: foo
+  configFn:
+    container:
+      image: gcr.io/example/reconciler:v1
+  annotations:
+    config.kubernetes.io/local-config: "true"
+spec:
+  replicas: 3
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  labels:
+    app: nginx
+  name: bar
+  annotations:
+    app: nginx
+spec:
+  replicas: 3
+`), 0600)
+	if !assert.NoError(t, err) {
+		return
+	}
+
+	f, err := ioutil.TempFile("", "kustomize-cat-test-dest")
+	if !assert.NoError(t, err) {
+		return
+	}
+	defer os.RemoveAll(d)
+
+	// fmt the files
+	b := &bytes.Buffer{}
+	r := cmd.GetCatRunner("")
+	r.Command.SetArgs([]string{d, "--dest", f.Name()})
+	r.Command.SetOut(b)
+	if !assert.NoError(t, r.Command.Execute()) {
+		return
+	}
+
+	if !assert.Equal(t, ``, b.String()) {
+		return
+	}
+
+	actual, err := ioutil.ReadFile(f.Name())
+	if !assert.NoError(t, err) {
+		return
+	}
+	if !assert.Equal(t, `kind: Deployment
+metadata:
+  labels:
+    app: nginx2
+  name: foo
+  annotations:
+    app: nginx2
+    config.kubernetes.io/package: .
+    config.kubernetes.io/path: f1.yaml
+spec:
+  replicas: 1
+---
+kind: Service
+metadata:
+  name: foo
+  annotations:
+    app: nginx
+    config.kubernetes.io/package: .
+    config.kubernetes.io/path: f1.yaml
+spec:
+  selector:
+    app: nginx
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: bar
+  labels:
+    app: nginx
+  annotations:
+    app: nginx
+    config.kubernetes.io/package: .
+    config.kubernetes.io/path: f2.yaml
+spec:
+  replicas: 3
+`, string(actual)) {
+		return
+	}
+}
+
+func TestCmd_outputCreateFile(t *testing.T) {
+	d, err := ioutil.TempDir("", "kustomize-cat-test")
+	if !assert.NoError(t, err) {
+		return
+	}
+	defer os.RemoveAll(d)
+
+	err = ioutil.WriteFile(filepath.Join(d, "f1.yaml"), []byte(`
+kind: Deployment
+metadata:
+  labels:
+    app: nginx2
+  name: foo
+  annotations:
+    app: nginx2
+spec:
+  replicas: 1
+---
+kind: Service
+metadata:
+  name: foo
+  annotations:
+    app: nginx
+spec:
+  selector:
+    app: nginx
+`), 0600)
+	if !assert.NoError(t, err) {
+		return
+	}
+	err = ioutil.WriteFile(filepath.Join(d, "f2.yaml"), []byte(`
+apiVersion: v1
+kind: Abstraction
+metadata:
+  name: foo
+  configFn:
+    container:
+      image: gcr.io/example/reconciler:v1
+  annotations:
+    config.kubernetes.io/local-config: "true"
+spec:
+  replicas: 3
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  labels:
+    app: nginx
+  name: bar
+  annotations:
+    app: nginx
+spec:
+  replicas: 3
+`), 0600)
+	if !assert.NoError(t, err) {
+		return
+	}
+
+	d2, err := ioutil.TempDir("", "kustomize-cat-test-dest")
+	if !assert.NoError(t, err) {
+		return
+	}
+	defer os.RemoveAll(d2)
+	f := filepath.Join(d2, "output.yaml")
+
+	// fmt the files
+	b := &bytes.Buffer{}
+	r := cmd.GetCatRunner("")
+	r.Command.SetArgs([]string{d, "--dest", f})
+	r.Command.SetOut(b)
+	if !assert.NoError(t, r.Command.Execute()) {
+		return
+	}
+
+	if !assert.Equal(t, ``, b.String()) {
+		return
+	}
+
+	actual, err := ioutil.ReadFile(f)
+	if !assert.NoError(t, err) {
+		return
+	}
+	if !assert.Equal(t, `kind: Deployment
+metadata:
+  labels:
+    app: nginx2
+  name: foo
+  annotations:
+    app: nginx2
+    config.kubernetes.io/package: .
+    config.kubernetes.io/path: f1.yaml
+spec:
+  replicas: 1
+---
+kind: Service
+metadata:
+  name: foo
+  annotations:
+    app: nginx
+    config.kubernetes.io/package: .
+    config.kubernetes.io/path: f1.yaml
+spec:
+  selector:
+    app: nginx
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: bar
+  labels:
+    app: nginx
+  annotations:
+    app: nginx
+    config.kubernetes.io/package: .
+    config.kubernetes.io/path: f2.yaml
+spec:
+  replicas: 3
+`, string(actual)) {
+		return
+	}
+}