command: make sure errors from flag go to UI [GH-269]

CHANGELOG.md

@@ -12,6 +12,7 @@ BUG FIXES:
   * core: Fix certain syntax of configuration that could cause hang. [GH-261]
   * core: `-no-color` flag properly disables color. [GH-250]
   * core: "~" is expanded in `-var-file` flags. [GH-273]
+  * core: Errors with tfvars are shown in console. [GH-269]
   * providers/aws: Refreshing EIP from pre-0.2 state file won't error. [GH-258]
   * providers/google: Attaching a disk source (not an image) works
       properly. [GH-254]

command/meta.go

@@ -1,8 +1,10 @@
 package command
 
 import (
+	"bufio"
 	"flag"
 	"fmt"
+	"io"
 	"math/rand"
 	"os"
 
@@ -137,6 +139,19 @@ func (m *Meta) flagSet(n string) *flag.FlagSet {
 		f.Var((*FlagVarFile)(&m.autoVariables), m.autoKey, "variable file")
 	}
 
+	// Create an io.Writer that writes to our Ui properly for errors.
+	// This is kind of a hack, but it does the job. Basically: create
+	// a pipe, use a scanner to break it into lines, and output each line
+	// to the UI. Do this forever.
+	errR, errW := io.Pipe()
+	errScanner := bufio.NewScanner(errR)
+	go func() {
+		for errScanner.Scan() {
+			m.Ui.Error(errScanner.Text())
+		}
+	}()
+	f.SetOutput(errW)
+
 	return f
 }