feat: add 'cat' command for displaying package resources

Signed-off-by: Aravindhan Ayyanathan <aravindhan.a@est.tech>

Author: aravindtga

commands/pkg/pkgcmd.go

@@ -1,4 +1,4 @@
-// Copyright 2019 The kpt Authors
+// Copyright 2019-2026 The kpt Authors
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -22,6 +22,7 @@ import (
 	initialization "github.com/kptdev/kpt/commands/pkg/init"
 	"github.com/kptdev/kpt/commands/pkg/update"
 	"github.com/kptdev/kpt/internal/docs/generated/pkgdocs"
+	"github.com/kptdev/kpt/thirdparty/cmdconfig/commands/cmdcat"
 	"github.com/kptdev/kpt/thirdparty/cmdconfig/commands/cmdtree"
 	"github.com/spf13/cobra"
 )
@@ -47,7 +48,7 @@ func GetCommand(ctx context.Context, name string) *cobra.Command {
 	pkg.AddCommand(
 		get.NewCommand(ctx, name), initialization.NewCommand(ctx, name),
 		update.NewCommand(ctx, name), diff.NewCommand(ctx, name),
-		cmdtree.NewCommand(ctx, name),
+		cmdtree.NewCommand(ctx, name), cmdcat.NewCommand(ctx, name),
 	)
 	return pkg
 }

thirdparty/cmdconfig/commands/cmdcat/cmdcat.go

@@ -0,0 +1,161 @@
+// Copyright 2019-2026 The Kpt Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package cmdcat
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/kptdev/kpt/internal/docs/generated/pkgdocs"
+	kptfilev1 "github.com/kptdev/kpt/pkg/api/kptfile/v1"
+	"github.com/kptdev/kpt/thirdparty/cmdconfig/commands/runner"
+	"github.com/spf13/cobra"
+	"sigs.k8s.io/kustomize/kyaml/kio"
+	"sigs.k8s.io/kustomize/kyaml/kio/filters"
+	"sigs.k8s.io/kustomize/kyaml/yaml"
+)
+
+// GetCatRunner returns a command CatRunner.
+func GetCatRunner(ctx context.Context, _ string) *CatRunner {
+	r := &CatRunner{
+		Ctx:       ctx,
+		errWriter: os.Stderr,
+	}
+	c := &cobra.Command{
+		Use:     "cat [FILE | DIR]",
+		Short:   pkgdocs.CatShort,
+		Long:    pkgdocs.CatLong,
+		Example: pkgdocs.CatExamples,
+		RunE:    r.runE,
+		Args:    cobra.MaximumNArgs(1),
+	}
+	c.Flags().BoolVar(&r.Format, "format", true,
+		"format resource config yaml before printing.")
+	c.Flags().BoolVar(&r.KeepAnnotations, "annotate", false,
+		"annotate resources with their file origins.")
+	c.Flags().StringSliceVar(&r.Styles, "style", []string{},
+		"yaml styles to apply.  may be 'TaggedStyle', 'DoubleQuotedStyle', 'LiteralStyle', "+
+			"'FoldedStyle', 'FlowStyle'.")
+	c.Flags().BoolVar(&r.StripComments, "strip-comments", false,
+		"remove comments from yaml.")
+	c.Flags().BoolVarP(&r.RecurseSubPackages, "recurse-subpackages", "R", true,
+		"print resources recursively in all the nested subpackages")
+	r.Command = c
+	return r
+}
+
+func NewCommand(ctx context.Context, name string) *cobra.Command {
+	return GetCatRunner(ctx, name).Command
+}
+
+// CatRunner contains the run function
+type CatRunner struct {
+	Command            *cobra.Command
+	Ctx                context.Context
+	Format             bool
+	KeepAnnotations    bool
+	Styles             []string
+	StripComments      bool
+	RecurseSubPackages bool
+	errWriter          io.Writer
+}
+
+func (r *CatRunner) runE(c *cobra.Command, args []string) error {
+	var writer = c.OutOrStdout()
+	if len(args) == 0 {
+		args = append(args, ".")
+	}
+
+	if info, err := os.Stat(args[0]); err == nil && !info.IsDir() {
+		switch strings.ToLower(filepath.Ext(args[0])) {
+		case ".yaml", ".yml", ".json":
+		default:
+			return fmt.Errorf("%q is not a YAML/JSON file; no resources will be read", args[0])
+		}
+	}
+
+	out := &bytes.Buffer{}
+	e := runner.ExecuteCmdOnPkgs{
+		Writer:             out,
+		NeedOpenAPI:        false,
+		RecurseSubPackages: r.RecurseSubPackages,
+		CmdRunner:          r,
+		RootPkgPath:        filepath.Clean(args[0]),
+		SkipPkgPathPrint:   true,
+	}
+
+	err := e.Execute()
+	if err != nil {
+		return err
+	}
+
+	res := strings.TrimSuffix(out.String(), "---\n")
+	res = strings.TrimSuffix(res, "---")
+	fmt.Fprintf(writer, "%s", res)
+
+	return nil
+}
+
+func (r *CatRunner) ExecuteCmd(w io.Writer, pkgPath string) error {
+	input := kio.LocalPackageReader{PackagePath: pkgPath, PackageFileName: kptfilev1.KptFileName}
+	out := &bytes.Buffer{}
+	err := kio.Pipeline{
+		Inputs:  []kio.Reader{input},
+		Filters: r.catFilters(),
+		Outputs: r.out(out),
+	}.Execute()
+
+	if err != nil {
+		// Emit a contextual diagnostic on stderr so the user knows which
+		// package failed; the runner currently aborts on the first error.
+		fmt.Fprintf(r.errWriter, "kpt pkg cat: %s in package %q\n", err.Error(), pkgPath)
+		return err
+	}
+	fmt.Fprint(w, out.String())
+	if out.String() != "" {
+		fmt.Fprint(w, "---")
+	}
+	return nil
+}
+
+func (r *CatRunner) catFilters() []kio.Filter {
+	var fltrs []kio.Filter
+	if r.Format {
+		fltrs = append(fltrs, filters.FormatFilter{})
+	}
+	if r.StripComments {
+		fltrs = append(fltrs, filters.StripCommentsFilter{})
+	}
+	return fltrs
+}
+
+func (r *CatRunner) out(w io.Writer) []kio.Writer {
+	var outputs []kio.Writer
+	var functionConfig *yaml.RNode
+
+	// remove these annotations explicitly; the ByteWriter won't clear them by
+	// default because they were set by the LocalPackageReader, not by it.
+	clear := []string{
+		"config.kubernetes.io/path",
+		"internal.config.kubernetes.io/path",
+	}
+	if r.KeepAnnotations {
+		clear = nil
+	}
+
+	outputs = append(outputs, kio.ByteWriter{
+		Writer:                w,
+		KeepReaderAnnotations: r.KeepAnnotations,
+		FunctionConfig:        functionConfig,
+		Style:                 yaml.GetStyle(r.Styles...),
+		ClearAnnotations:      clear,
+	})
+
+	return outputs
+}