borrow wrappedreadline workarounds from terraform and implement a similar check for piped commands; this makes the cli experience much cleaner

command/console.go

@@ -1,11 +1,14 @@
 package command
 
 import (
+	"bufio"
 	"errors"
 	"fmt"
 	"io"
 	"strings"
 
+	"github.com/chzyer/readline"
+	"github.com/hashicorp/packer/helper/wrappedreadline"
 	"github.com/hashicorp/packer/packer"
 	"github.com/hashicorp/packer/template"
 	"github.com/hashicorp/packer/template/interpolate"
@@ -70,6 +73,11 @@ func (c *ConsoleCommand) Run(args []string) int {
 		Core: core,
 	}
 
+	// Determine if stdin is a pipe. If so, we evaluate directly.
+	if c.StdinPiped() {
+		return c.modePiped(session)
+	}
+
 	return c.modeInteractive(session)
 }
 
@@ -105,12 +113,45 @@ func (*ConsoleCommand) AutocompleteFlags() complete.Flags {
 	}
 }
 
-func (c *ConsoleCommand) modeInteractive(session *REPLSession) int {
+func (c *ConsoleCommand) modePiped(session *REPLSession) int {
+	var lastResult string
+	scanner := bufio.NewScanner(wrappedreadline.Stdin())
+	for scanner.Scan() {
+		result, err := session.Handle(strings.TrimSpace(scanner.Text()))
+		if err != nil {
+			return 0
+		}
+		// Store the last result
+		lastResult = result
+	}
+
+	// Output the final result
+	c.Ui.Message(lastResult)
+	return 0
+}
+
+func (c *ConsoleCommand) modeInteractive(session *REPLSession) int { // Setup the UI so we can output directly to stdout
+	l, err := readline.NewEx(wrappedreadline.Override(&readline.Config{
+		Prompt:            "> ",
+		InterruptPrompt:   "^C",
+		EOFPrompt:         "exit",
+		HistorySearchFold: true,
+	}))
+	if err != nil {
+		c.Ui.Error(fmt.Sprintf(
+			"Error initializing console: %s",
+			err))
+		return 1
+	}
 	for {
 		// Read a line
-		line, err := c.Ui.Ask("> ")
-		if err == packer.ErrInterrupted {
-			break
+		line, err := l.Readline()
+		if err == readline.ErrInterrupt {
+			if len(line) == 0 {
+				break
+			} else {
+				continue
+			}
 		} else if err == io.EOF {
 			break
 		}
@@ -144,6 +185,8 @@ type REPLSession struct {
 // The return value is the output and the error to show.
 func (s *REPLSession) Handle(line string) (string, error) {
 	switch {
+	case strings.TrimSpace(line) == "":
+		return "", nil
 	case strings.TrimSpace(line) == "exit":
 		return "", ErrSessionExit
 	case strings.TrimSpace(line) == "help":

command/meta.go

@@ -5,9 +5,11 @@ import (
 	"flag"
 	"fmt"
 	"io"
+	"os"
 
 	kvflag "github.com/hashicorp/packer/helper/flag-kv"
 	sliceflag "github.com/hashicorp/packer/helper/flag-slice"
+	"github.com/hashicorp/packer/helper/wrappedreadline"
 	"github.com/hashicorp/packer/packer"
 	"github.com/hashicorp/packer/template"
 )
@@ -140,3 +142,14 @@ func (m *Meta) ValidateFlags() error {
 	// TODO
 	return nil
 }
+
+// StdinPiped returns true if the input is piped.
+func (m *Meta) StdinPiped() bool {
+	fi, err := wrappedreadline.Stdin().Stat()
+	if err != nil {
+		// If there is an error, let's just say its not piped
+		return false
+	}
+
+	return fi.Mode()&os.ModeNamedPipe != 0
+}

go.mod

@@ -22,6 +22,7 @@ require (
 	github.com/biogo/hts v0.0.0-20160420073057-50da7d4131a3
 	github.com/c2h5oh/datasize v0.0.0-20171227191756-4eba002a5eae
 	github.com/cheggaaa/pb v1.0.27
+	github.com/chzyer/readline v0.0.0-20180603132655-2972be24d48e
 	github.com/creack/goselect v0.1.0 // indirect
 	github.com/dgrijalva/jwt-go v3.2.0+incompatible
 	github.com/digitalocean/godo v1.11.1

go.sum

@@ -76,6 +76,8 @@ github.com/census-instrumentation/opencensus-proto v0.2.0 h1:LzQXZOgg4CQfE6bFvXG
 github.com/census-instrumentation/opencensus-proto v0.2.0/go.mod h1:f6KPmirojxKA12rnyqOA5BBL4O983OfeGPqjHWSTneU=
 github.com/cheggaaa/pb v1.0.27 h1:wIkZHkNfC7R6GI5w7l/PdAdzXzlrbcI3p8OAlnkTsnc=
 github.com/cheggaaa/pb v1.0.27/go.mod h1:pQciLPpbU0oxA0h+VJYYLxO+XeDQb5pZijXscXHm81s=
+github.com/chzyer/readline v0.0.0-20180603132655-2972be24d48e h1:fY5BOSpyZCqRo5OhCuC+XN+r/bBCmeuuJtjz+bCNIf8=
+github.com/chzyer/readline v0.0.0-20180603132655-2972be24d48e/go.mod h1:nSuG5e5PlCu98SY8svDHJxuZscDgtXS6KTTbou5AhLI=
 github.com/client9/misspell v0.3.4/go.mod h1:qj6jICC3Q7zFZvVWo7KLAzC3yx5G7kyvSDkc90ppPyw=
 github.com/coreos/go-systemd v0.0.0-20181012123002-c6f51f82210d/go.mod h1:F5haX7vjVVG0kc13fIWeqUViNPyEJxv/OmvnBo0Yme4=
 github.com/creack/goselect v0.1.0 h1:4QiXIhcpSQF50XGaBsFzesjwX/1qOY5bOveQPmN9CXY=

helper/wrappedreadline/wrappedreadline.go

@@ -0,0 +1,125 @@
+// Shamelessly copied from the Terraform repo because it wasn't worth vendoring
+// out two hundred lines of code so Packer could use it too.
+//
+// wrappedreadline is a package that has helpers for interacting with
+// readline from a panicwrap executable.
+//
+// panicwrap overrides the standard file descriptors so that the child process
+// no longer looks like a TTY. The helpers here access the extra file descriptors
+// passed by panicwrap to fix that.
+//
+// panicwrap should be checked for with panicwrap.Wrapped before using this
+// librar, since this library won't adapt if the binary is not wrapped.
+package wrappedreadline
+
+import (
+	"os"
+	"runtime"
+
+	"github.com/chzyer/readline"
+	"github.com/mitchellh/panicwrap"
+)
+
+// Override overrides the values in readline.Config that need to be
+// set with wrapped values.
+func Override(cfg *readline.Config) *readline.Config {
+	cfg.Stdin = Stdin()
+	cfg.Stdout = Stdout()
+	cfg.Stderr = Stderr()
+
+	cfg.FuncGetWidth = TerminalWidth
+	cfg.FuncIsTerminal = IsTerminal
+
+	rm := RawMode{StdinFd: int(Stdin().Fd())}
+	cfg.FuncMakeRaw = rm.Enter
+	cfg.FuncExitRaw = rm.Exit
+
+	return cfg
+}
+
+// IsTerminal determines if this process is attached to a TTY.
+func IsTerminal() bool {
+	// Windows is always a terminal
+	if runtime.GOOS == "windows" {
+		return true
+	}
+
+	// Same implementation as readline but with our custom fds
+	return readline.IsTerminal(int(Stdin().Fd())) &&
+		(readline.IsTerminal(int(Stdout().Fd())) ||
+			readline.IsTerminal(int(Stderr().Fd())))
+}
+
+// TerminalWidth gets the terminal width in characters.
+func TerminalWidth() int {
+	if runtime.GOOS == "windows" {
+		return readline.GetScreenWidth()
+	}
+
+	return getWidth()
+}
+
+// RawMode is a helper for entering and exiting raw mode.
+type RawMode struct {
+	StdinFd int
+
+	state *readline.State
+}
+
+func (r *RawMode) Enter() (err error) {
+	r.state, err = readline.MakeRaw(r.StdinFd)
+	return err
+}
+
+func (r *RawMode) Exit() error {
+	if r.state == nil {
+		return nil
+	}
+
+	return readline.Restore(r.StdinFd, r.state)
+}
+
+// Package provides access to the standard OS streams
+// (stdin, stdout, stderr) even if wrapped under panicwrap.
+// Stdin returns the true stdin of the process.
+func Stdin() *os.File {
+	stdin := os.Stdin
+	if panicwrap.Wrapped(nil) {
+		stdin = wrappedStdin
+	}
+
+	return stdin
+}
+
+// Stdout returns the true stdout of the process.
+func Stdout() *os.File {
+	stdout := os.Stdout
+	if panicwrap.Wrapped(nil) {
+		stdout = wrappedStdout
+	}
+
+	return stdout
+}
+
+// Stderr returns the true stderr of the process.
+func Stderr() *os.File {
+	stderr := os.Stderr
+	if panicwrap.Wrapped(nil) {
+		stderr = wrappedStderr
+	}
+
+	return stderr
+}
+
+// These are the wrapped standard streams. These are setup by the
+// platform specific code in initPlatform.
+var (
+	wrappedStdin  *os.File
+	wrappedStdout *os.File
+	wrappedStderr *os.File
+)
+
+func init() {
+	// Initialize the platform-specific code
+	initPlatform()
+}

helper/wrappedreadline/wrappedreadline_unix.go

@@ -0,0 +1,52 @@
+// +build darwin dragonfly freebsd linux,!appengine netbsd openbsd
+
+package wrappedreadline
+
+import (
+	"os"
+	"syscall"
+	"unsafe"
+)
+
+// getWidth impl for Unix
+func getWidth() int {
+	stdoutFd := int(Stdout().Fd())
+	stderrFd := int(Stderr().Fd())
+
+	w := getWidthFd(stdoutFd)
+	if w < 0 {
+		w = getWidthFd(stderrFd)
+	}
+
+	return w
+}
+
+type winsize struct {
+	Row    uint16
+	Col    uint16
+	Xpixel uint16
+	Ypixel uint16
+}
+
+// get width of the terminal
+func getWidthFd(stdoutFd int) int {
+	ws := &winsize{}
+	retCode, _, errno := syscall.Syscall(syscall.SYS_IOCTL,
+		uintptr(stdoutFd),
+		uintptr(syscall.TIOCGWINSZ),
+		uintptr(unsafe.Pointer(ws)))
+
+	if int(retCode) == -1 {
+		_ = errno
+		return -1
+	}
+
+	return int(ws.Col)
+}
+
+func initPlatform() {
+	// The standard streams are passed in via extra file descriptors.
+	wrappedStdin = os.NewFile(uintptr(3), "stdin")
+	wrappedStdout = os.NewFile(uintptr(4), "stdout")
+	wrappedStderr = os.NewFile(uintptr(5), "stderr")
+}

helper/wrappedreadline/wrappedreadline_windows.go

@@ -0,0 +1,57 @@
+// +build windows
+
+package wrappedreadline
+
+import (
+	"log"
+	"os"
+	"syscall"
+)
+
+// getWidth impl for other
+func getWidth() int {
+	return 0
+}
+
+func initPlatform() {
+	wrappedStdin = openConsole("CONIN$", os.Stdin)
+	wrappedStdout = openConsole("CONOUT$", os.Stdout)
+	wrappedStderr = wrappedStdout
+}
+
+// openConsole opens a console handle, using a backup if it fails.
+// This is used to get the exact console handle instead of the redirected
+// handles from panicwrap.
+func openConsole(name string, backup *os.File) *os.File {
+	// Convert to UTF16
+	path, err := syscall.UTF16PtrFromString(name)
+	if err != nil {
+		log.Printf("[ERROR] wrappedstreams: %s", err)
+		return backup
+	}
+
+	// Determine the share mode
+	var shareMode uint32
+	switch name {
+	case "CONIN$":
+		shareMode = syscall.FILE_SHARE_READ
+	case "CONOUT$":
+		shareMode = syscall.FILE_SHARE_WRITE
+	}
+
+	// Get the file
+	h, err := syscall.CreateFile(
+		path,
+		syscall.GENERIC_READ|syscall.GENERIC_WRITE,
+		shareMode,
+		nil,
+		syscall.OPEN_EXISTING,
+		0, 0)
+	if err != nil {
+		log.Printf("[ERROR] wrappedstreams: %s", err)
+		return backup
+	}
+
+	// Create the Go file
+	return os.NewFile(uintptr(h), name)
+}