New --exec-pipe output option

cmd/gomplate/main.go

@@ -5,6 +5,7 @@ The gomplate command
 package main
 
 import (
+	"bytes"
 	"fmt"
 	"os"
 	"os/exec"
@@ -19,8 +20,11 @@ import (
 var (
 	printVer bool
 	verbose  bool
+	execPipe bool
 	opts     gomplate.Config
 	includes []string
+
+	postRunInput *bytes.Buffer
 )
 
 func printVersion(name string) {
@@ -34,7 +38,11 @@ func postRunExec(cmd *cobra.Command, args []string) error {
 		args = args[1:]
 		// nolint: gosec
 		c := exec.Command(name, args...)
-		c.Stdin = os.Stdin
+		if execPipe {
+			c.Stdin = postRunInput
+		} else {
+			c.Stdin = os.Stdin
+		}
 		c.Stderr = os.Stderr
 		c.Stdout = os.Stdout
 
@@ -101,6 +109,10 @@ func newGomplateCmd() *cobra.Command {
 			// support --include
 			opts.ExcludeGlob = processIncludes(includes, opts.ExcludeGlob)
 
+			if execPipe {
+				postRunInput = &bytes.Buffer{}
+				opts.Out = postRunInput
+			}
 			err := gomplate.RunTemplates(&opts)
 			cmd.SilenceErrors = true
 			cmd.SilenceUsage = true
@@ -140,6 +152,8 @@ func initFlags(command *cobra.Command) {
 	command.Flags().StringVar(&opts.OutputMap, "output-map", "", "Template `string` to map the input file to an output path")
 	command.Flags().StringVar(&opts.OutMode, "chmod", "", "set the mode for output file(s). Omit to inherit from input file(s)")
 
+	command.Flags().BoolVar(&execPipe, "exec-pipe", false, "pipe the output to the post-run exec command")
+
 	ldDefault := env.Getenv("GOMPLATE_LEFT_DELIM", "{{")
 	rdDefault := env.Getenv("GOMPLATE_RIGHT_DELIM", "}}")
 	command.Flags().StringVar(&opts.LDelim, "left-delim", ldDefault, "override the default left-`delimiter` [$GOMPLATE_LEFT_DELIM]")

cmd/gomplate/validate.go

@@ -47,6 +47,10 @@ func validateOpts(cmd *cobra.Command, args []string) (err error) {
 		err = fmt.Errorf("must provide same number of --out (%d) as --file (%d) options", len(opts.OutputFiles), len(opts.InputFiles))
 	}
 
+	if err == nil && cmd.Flag("exec-pipe").Changed && len(args) == 0 {
+		err = fmt.Errorf("--exec-pipe may only be used with a post-exec command after --")
+	}
+
 	if err == nil {
 		err = mustTogether(cmd, "output-dir", "input-dir")
 	}

cmd/gomplate/validate_test.go

@@ -42,6 +42,41 @@ func TestValidateOpts(t *testing.T) {
 	))
 	assert.Error(t, err)
 
+	err = validateOpts(parseFlags("--exec-pipe"))
+	assert.Error(t, err)
+
+	err = validateOpts(parseFlags("--exec-pipe", "--"))
+	assert.Error(t, err)
+
+	err = validateOpts(parseFlags(
+		"--exec-pipe",
+		"--", "echo", "foo",
+	))
+	assert.NoError(t, err)
+
+	err = validateOpts(parseFlags(
+		"--exec-pipe",
+		"--out", "foo",
+		"--", "echo",
+	))
+	assert.Error(t, err)
+
+	err = validateOpts(parseFlags(
+		"--input-dir", "in",
+		"--exec-pipe",
+		"--output-dir", "foo",
+		"--", "echo",
+	))
+	assert.Error(t, err)
+
+	err = validateOpts(parseFlags(
+		"--input-dir", "in",
+		"--exec-pipe",
+		"--output-map", "foo",
+		"--", "echo",
+	))
+	assert.Error(t, err)
+
 	err = validateOpts(parseFlags(
 		"--input-dir", "in",
 		"--output-map", "bar",

config.go

@@ -1,6 +1,7 @@
 package gomplate
 
 import (
+	"io"
 	"os"
 	"strconv"
 	"strings"
@@ -17,6 +18,7 @@ type Config struct {
 	OutputDir   string
 	OutputMap   string
 	OutMode     string
+	Out         io.Writer
 
 	DataSources       []string
 	DataSourceHeaders []string

docs/content/usage.md

@@ -232,6 +232,21 @@ By default, plugins will time out after 5 seconds. To adjust this, set the
 `GOMPLATE_PLUGIN_TIMEOUT` environment variable to a valid [duration](../functions/time/#time-parseduration)
 such as `10s` or `3m`.
 
+### `--exec-pipe`
+
+When using [post-template command execution](#post-template-command-execution),
+it may be useful to pipe gomplate's rendered output directly into the command's
+standard input.
+
+To do this, simply use `--exec-pipe` instead of `--out` or any other output flag:
+
+```console
+$ gomplate -i 'hello world' --exec-pipe -- tr a-z A-Z
+HELLO WORLD
+```
+
+Note that multiple inputs are not yet supported when using this option.
+
 ## Post-template command execution
 
 Gomplate can launch other commands when template execution is successful. Simply
@@ -242,6 +257,9 @@ $ gomplate -i 'hello world' -o out.txt -- cat out.txt
 hello world
 ```
 
+See also [`--exec-pipe`](#exec-pipe) for piping output directly into the
+post-exec command.
+
 ## Suppressing empty output
 
 Sometimes it can be desirable to suppress empty output (i.e. output consisting of only whitespace). To do so, set `GOMPLATE_SUPPRESS_EMPTY=true` in your environment:

gomplate_test.go

@@ -2,7 +2,6 @@ package gomplate
 
 import (
 	"bytes"
-	"io"
 	"net/http/httptest"
 	"os"
 	"path/filepath"
@@ -19,15 +18,6 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
-// like ioutil.NopCloser(), except for io.WriteClosers...
-type nopWCloser struct {
-	io.Writer
-}
-
-func (n *nopWCloser) Close() error {
-	return nil
-}
-
 func testTemplate(g *gomplate, tmpl string) string {
 	var out bytes.Buffer
 	err := g.runTemplate(&tplate{name: "testtemplate", contents: tmpl, target: &out})

template.go

@@ -103,6 +103,11 @@ func gatherTemplates(o *Config, outFileNamer func(string) (string, error)) (temp
 		return nil, err
 	}
 
+	// --exec-pipe redirects standard out to the out pipe
+	if o.Out != nil {
+		Stdout = &nopWCloser{o.Out}
+	}
+
 	switch {
 	// the arg-provided input string gets a special name
 	case o.Input != "":
@@ -336,3 +341,12 @@ func allWhitespace(p []byte) bool {
 	}
 	return true
 }
+
+// like ioutil.NopCloser(), except for io.WriteClosers...
+type nopWCloser struct {
+	io.Writer
+}
+
+func (n *nopWCloser) Close() error {
+	return nil
+}

tests/integration/basic_test.go

@@ -184,6 +184,17 @@ func (s *BasicSuite) TestExecCommand(c *C) {
 	})
 }
 
+func (s *BasicSuite) TestPostRunExecPipe(c *C) {
+	result := icmd.RunCmd(icmd.Command(GomplateBin,
+		"-i", `{{print "hello world"}}`,
+		"--exec-pipe",
+		"--", "tr", "a-z", "A-Z"))
+	result.Assert(c, icmd.Expected{
+		ExitCode: 0,
+		Out:      "HELLO WORLD",
+	})
+}
+
 func (s *BasicSuite) TestEmptyOutputSuppression(c *C) {
 	out := s.tmpDir.Join("out")
 	result := icmd.RunCmd(icmd.Command(GomplateBin,