Execute additional command after --

Signed-off-by: Dave Henderson <dhenderson@gmail.com>

3 files changed, 49 insertions, 2 deletions

diff --git a/cmd/gomplate/main.go b/cmd/gomplate/main.go
index 256bed1f..1fcb1a5b 100644
--- a/cmd/gomplate/main.go
+++ b/cmd/gomplate/main.go
@@ -4,6 +4,7 @@ import (
 	"errors"
 	"fmt"
 	"os"
+	"os/exec"
 
 	"github.com/hairyhenderson/gomplate"
 	"github.com/hairyhenderson/gomplate/env"
@@ -45,6 +46,29 @@ func printVersion(name string) {
 	fmt.Printf("%s version %s\n", name, version.Version)
 }
 
+// postRunExec - if templating succeeds, the command following a '--' will be executed
+func postRunExec(cmd *cobra.Command, args []string) error {
+	if len(args) > 0 {
+		name := args[0]
+		args = args[1:]
+		c := exec.Command(name, args...)
+		c.Stdin = os.Stdin
+		c.Stderr = os.Stderr
+		c.Stdout = os.Stdout
+		return c.Run()
+	}
+	return nil
+}
+
+// optionalExecArgs - implements cobra.PositionalArgs. Allows extra args following
+// a '--', but not otherwise.
+func optionalExecArgs(cmd *cobra.Command, args []string) error {
+	if cmd.ArgsLenAtDash() == 0 {
+		return nil
+	}
+	return cobra.NoArgs(cmd, args)
+}
+
 func newGomplateCmd() *cobra.Command {
 	rootCmd := &cobra.Command{
 		Use:     "gomplate",
@@ -57,7 +81,8 @@ func newGomplateCmd() *cobra.Command {
 			}
 			return gomplate.RunTemplates(&opts)
 		},
-		Args: cobra.NoArgs,
+		PostRunE: postRunExec,
+		Args:     optionalExecArgs,
 	}
 	return rootCmd
 }
diff --git a/docs/content/usage.md b/docs/content/usage.md
index de4ec93b..30f931dd 100644
--- a/docs/content/usage.md
+++ b/docs/content/usage.md
@@ -74,3 +74,13 @@ A few different forms are valid:
 
 Sometimes it's necessary to override the default template delimiters (`{{`/`}}`).
 Use `--left-delim`/`--right-delim` or set `$GOMPLATE_LEFT_DELIM`/`$GOMPLATE_RIGHT_DELIM`.
+
+## Post-template command execution
+
+Gomplate can launch other commands when template execution is successful. Simply
+add the command to the command-line after a `--` argument:
+
+```console
+$ gomplate -i 'hello world' -o out.txt -- cat out.txt
+hello world
+```
diff --git a/test/integration/basic_test.go b/test/integration/basic_test.go
index c0a52a0b..2565341b 100644
--- a/test/integration/basic_test.go
+++ b/test/integration/basic_test.go
@@ -1,4 +1,4 @@
-//+build integration
+// +build integration
 //+build !windows
 
 package integration
@@ -152,3 +152,15 @@ func (s *BasicSuite) TestUnknownArgErrors(c *C) {
 	result := icmd.RunCommand(GomplateBin, "-in", "flibbit")
 	result.Assert(c, icmd.Expected{ExitCode: 1, Out: `unknown command "flibbit" for "gomplate"`})
 }
+
+func (s *BasicSuite) TestExecCommand(c *C) {
+	out := s.tmpDir.Join("out")
+	result := icmd.RunCmd(icmd.Command(GomplateBin,
+		"-i", `{{print "hello world"}}`,
+		"-o", out,
+		"--", "cat", out))
+	result.Assert(c, icmd.Expected{
+		ExitCode: 0,
+		Out:      "hello world",
+	})
+}