diff --git a/interpreter.go b/interpreter.go
index 99f5bcc..90002a7 100644
--- a/interpreter.go
+++ b/interpreter.go
@@ -724,7 +724,7 @@ func serializeJSON(v interface{}, multiline bool, indent string, buf *bytes.Buff
 }
 
 func (i *interpreter) manifestAndSerializeJSON(
-		buf *bytes.Buffer, trace *TraceElement, v value, multiline bool, indent string) error {
+	buf *bytes.Buffer, trace *TraceElement, v value, multiline bool, indent string) error {
 	manifested, err := i.manifestJSON(trace, v)
 	if err != nil {
 		return err
@@ -740,10 +740,55 @@ func (i *interpreter) manifestString(buf *bytes.Buffer, trace *TraceElement, v v
 		buf.WriteString(v.getString())
 		return nil
 	default:
-		return makeRuntimeError(fmt.Sprint("Expected string result, got: " + v.getType().name), i.getCurrentStackTrace(trace))
+		return makeRuntimeError(fmt.Sprintf("Expected string result, got: %s", v.getType().name), i.getCurrentStackTrace(trace))
 	}
 }
 
+func (i *interpreter) manifestAndSerializeMulti(trace *TraceElement, v value) (r map[string]string, err error) {
+	r = make(map[string]string)
+	json, err := i.manifestJSON(trace, v)
+	if err != nil {
+		return r, err
+	}
+	switch json := json.(type) {
+	case map[string]interface{}:
+		for filename, fileJson := range json {
+			var buf bytes.Buffer
+			serializeJSON(fileJson, true, "", &buf)
+			buf.WriteString("\n")
+			r[filename] = buf.String()
+		}
+	default:
+		msg := fmt.Sprintf("Multi mode: Top-level object was a %s, "+
+			"should be an object whose keys are filenames and values hold "+
+			"the JSON for that file.", v.getType().name)
+		return r, makeRuntimeError(msg, i.getCurrentStackTrace(trace))
+	}
+	return
+}
+
+func (i *interpreter) manifestAndSerializeYAMLStream(trace *TraceElement, v value) (r []string, err error) {
+	r = make([]string, 0)
+	json, err := i.manifestJSON(trace, v)
+	if err != nil {
+		return r, err
+	}
+	switch json := json.(type) {
+	case []interface{}:
+		for _, doc := range json {
+			var buf bytes.Buffer
+			serializeJSON(doc, true, "", &buf)
+			buf.WriteString("\n")
+			r = append(r, buf.String())
+		}
+	default:
+		msg := fmt.Sprintf("Stream mode: Top-level object was a %s, "+
+			"should be an array whose elements hold "+
+			"the JSON for each document in the stream.", v.getType().name)
+		return r, makeRuntimeError(msg, i.getCurrentStackTrace(trace))
+	}
+	return
+}
 
 func jsonToValue(e *evaluator, v interface{}) (value, error) {
 	switch v := v.(type) {
@@ -890,13 +935,7 @@ func makeInitialEnv(filename string, baseStd valueObject) environment {
 	)
 }
 
-// TODO(sbarzowski) this function takes far too many arguments - build interpreter in vm instead
-func evaluate(node ast.Node, ext vmExtMap, tla vmExtMap, nativeFuncs map[string]*NativeFunction,
-              maxStack int, importer Importer, stringOutput bool) (string, error) {
-	i, err := buildInterpreter(ext, nativeFuncs, maxStack, importer)
-	if err != nil {
-		return "", err
-	}
+func evaluateAux(i *interpreter, node ast.Node, tla vmExtMap) (value, *TraceElement, error) {
 	evalLoc := ast.MakeLocationRangeMessage("During evaluation")
 	evalTrace := &TraceElement{
 		loc: &evalLoc,
@@ -904,7 +943,7 @@ func evaluate(node ast.Node, ext vmExtMap, tla vmExtMap, nativeFuncs map[string]
 	env := makeInitialEnv(node.Loc().FileName, i.baseStd)
 	result, err := i.EvalInCleanEnv(evalTrace, &env, node, false)
 	if err != nil {
-		return "", err
+		return nil, nil, err
 	}
 	if len(tla) != 0 {
 		// If it's not a function, ignore TLA
@@ -914,13 +953,13 @@ func evaluate(node ast.Node, ext vmExtMap, tla vmExtMap, nativeFuncs map[string]
 			for argName, pv := range toplevelArgMap {
 				args.named = append(args.named, namedCallArgument{name: ast.Identifier(argName), pv: pv})
 			}
-			funcLoc := ast.MakeLocationRangeMessage("Top-level-function")
+			funcLoc := ast.MakeLocationRangeMessage("Top-level function")
 			funcTrace := &TraceElement{
 				loc: &funcLoc,
 			}
 			result, err = f.call(args).getValue(i, funcTrace)
 			if err != nil {
-				return "", err
+				return nil, nil, err
 			}
 		}
 	}
@@ -928,6 +967,23 @@ func evaluate(node ast.Node, ext vmExtMap, tla vmExtMap, nativeFuncs map[string]
 	manifestationTrace := &TraceElement{
 		loc: &manifestationLoc,
 	}
+	return result, manifestationTrace, nil
+}
+
+// TODO(sbarzowski) this function takes far too many arguments - build interpreter in vm instead
+func evaluate(node ast.Node, ext vmExtMap, tla vmExtMap, nativeFuncs map[string]*NativeFunction,
+	maxStack int, importer Importer, stringOutput bool) (string, error) {
+
+	i, err := buildInterpreter(ext, nativeFuncs, maxStack, importer)
+	if err != nil {
+		return "", err
+	}
+
+	result, manifestationTrace, err := evaluateAux(i, node, tla)
+	if err != nil {
+		return "", err
+	}
+
 	var buf bytes.Buffer
 	if stringOutput {
 		err = i.manifestString(&buf, manifestationTrace, result)
@@ -940,3 +996,37 @@ func evaluate(node ast.Node, ext vmExtMap, tla vmExtMap, nativeFuncs map[string]
 	buf.WriteString("\n")
 	return buf.String(), nil
 }
+
+// TODO(sbarzowski) this function takes far too many arguments - build interpreter in vm instead
+func evaluateMulti(node ast.Node, ext vmExtMap, tla vmExtMap, nativeFuncs map[string]*NativeFunction,
+	maxStack int, importer Importer, stringOutput bool) (map[string]string, error) {
+
+	i, err := buildInterpreter(ext, nativeFuncs, maxStack, importer)
+	if err != nil {
+		return nil, err
+	}
+
+	result, manifestationTrace, err := evaluateAux(i, node, tla)
+	if err != nil {
+		return nil, err
+	}
+
+	return i.manifestAndSerializeMulti(manifestationTrace, result)
+}
+
+// TODO(sbarzowski) this function takes far too many arguments - build interpreter in vm instead
+func evaluateStream(node ast.Node, ext vmExtMap, tla vmExtMap, nativeFuncs map[string]*NativeFunction,
+	maxStack int, importer Importer) ([]string, error) {
+
+	i, err := buildInterpreter(ext, nativeFuncs, maxStack, importer)
+	if err != nil {
+		return nil, err
+	}
+
+	result, manifestationTrace, err := evaluateAux(i, node, tla)
+	if err != nil {
+		return nil, err
+	}
+
+	return i.manifestAndSerializeYAMLStream(manifestationTrace, result)
+}
diff --git a/jsonnet/cmd.go b/jsonnet/cmd.go
index fba14ab..b617dec 100644
--- a/jsonnet/cmd.go
+++ b/jsonnet/cmd.go
@@ -18,20 +18,145 @@ package main
 
 import (
 	"fmt"
+	"io"
 	"io/ioutil"
 	"log"
 	"os"
 	"runtime/pprof"
+	"sort"
+	"strconv"
 	"strings"
 
 	"github.com/google/go-jsonnet"
 )
 
-func usage() {
-	fmt.Println("usage: jsonnet <filename>")
+func nextArg(i *int, args []string) string {
+	(*i)++
+	if (*i) >= len(args) {
+		fmt.Fprintln(os.Stderr, "Expected another commandline argument.")
+		os.Exit(1)
+	}
+	return args[*i]
 }
 
-func getVar(s string) (string, string, error) {
+// simplifyArgs transforms an array of commandline arguments so that
+// any -abc arg before the first -- (if any) are expanded into
+// -a -b -c.
+func simplifyArgs(args []string) (r []string) {
+	r = make([]string, 0, len(args)*2)
+	for i, arg := range args {
+		if arg == "--" {
+			for j := i; j < len(args); j++ {
+				r = append(r, args[j])
+			}
+			break
+		}
+		if len(arg) > 2 && arg[0] == '-' && arg[1] != '-' {
+			for j := 1; j < len(arg); j++ {
+				r = append(r, "-"+string(arg[j]))
+			}
+		} else {
+			r = append(r, arg)
+		}
+	}
+	return
+}
+
+func version(o io.Writer) {
+	fmt.Fprintf(o, "Jsonnet commandline interpreter %s\n", jsonnet.Version())
+}
+
+func usage(o io.Writer) {
+	version(o)
+	fmt.Fprintln(o)
+	fmt.Fprintln(o, "General commandline:")
+	fmt.Fprintln(o, "jsonnet [<cmd>] {<option>} { <filename> }")
+	fmt.Fprintln(o, "Note: <cmd> defaults to \"eval\"")
+	fmt.Fprintln(o)
+	fmt.Fprintln(o, "The eval command:")
+	fmt.Fprintln(o, "jsonnet eval {<option>} <filename>")
+	fmt.Fprintln(o, "Note: Only one filename is supported")
+	fmt.Fprintln(o)
+	fmt.Fprintln(o, "Available eval options:")
+	fmt.Fprintln(o, "  -h / --help             This message")
+	fmt.Fprintln(o, "  -e / --exec             Treat filename as code")
+	fmt.Fprintln(o, "  -J / --jpath <dir>      Specify an additional library search dir")
+	fmt.Fprintln(o, "  -o / --output-file <file> Write to the output file rather than stdout")
+	fmt.Fprintln(o, "  -m / --multi <dir>      Write multiple files to the directory, list files on stdout")
+	fmt.Fprintln(o, "  -y / --yaml-stream      Write output as a YAML stream of JSON documents")
+	fmt.Fprintln(o, "  -S / --string           Expect a string, manifest as plain text")
+	fmt.Fprintln(o, "  -s / --max-stack <n>    Number of allowed stack frames")
+	fmt.Fprintln(o, "  -t / --max-trace <n>    Max length of stack trace before cropping")
+	fmt.Fprintln(o, "  --version               Print version")
+	fmt.Fprintln(o, "Available options for specifying values of 'external' variables:")
+	fmt.Fprintln(o, "Provide the value as a string:")
+	fmt.Fprintln(o, "  -V / --ext-str <var>[=<val>]     If <val> is omitted, get from environment var <var>")
+	fmt.Fprintln(o, "       --ext-str-file <var>=<file> Read the string from the file")
+	fmt.Fprintln(o, "Provide a value as Jsonnet code:")
+	fmt.Fprintln(o, "  --ext-code <var>[=<code>]    If <code> is omitted, get from environment var <var>")
+	fmt.Fprintln(o, "  --ext-code-file <var>=<file> Read the code from the file")
+	fmt.Fprintln(o, "Available options for specifying values of 'top-level arguments':")
+	fmt.Fprintln(o, "Provide the value as a string:")
+	fmt.Fprintln(o, "  -A / --tla-str <var>[=<val>]     If <val> is omitted, get from environment var <var>")
+	fmt.Fprintln(o, "       --tla-str-file <var>=<file> Read the string from the file")
+	fmt.Fprintln(o, "Provide a value as Jsonnet code:")
+	fmt.Fprintln(o, "  --tla-code <var>[=<code>]    If <code> is omitted, get from environment var <var>")
+	fmt.Fprintln(o, "  --tla-code-file <var>=<file> Read the code from the file")
+	fmt.Fprintln(o)
+	fmt.Fprintln(o, "The fmt command:")
+	fmt.Fprintln(o, "jsonnet fmt is currently not available in the Go implementation")
+	fmt.Fprintln(o)
+	fmt.Fprintln(o, "In all cases:")
+	fmt.Fprintln(o, "<filename> can be - (stdin)")
+	fmt.Fprintln(o, "Multichar options are expanded e.g. -abc becomes -a -b -c.")
+	fmt.Fprintln(o, "The -- option suppresses option processing for subsequent arguments.")
+	fmt.Fprintln(o, "Note that since filenames and jsonnet programs can begin with -, it is advised to")
+	fmt.Fprintln(o, "use -- if the argument is unknown, e.g. jsonnet -- \"$FILENAME\".")
+}
+
+func safeStrToInt(str string) (i int) {
+	i, err := strconv.Atoi(str)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, "ERROR: Invalid integer \"%s\"", str)
+		os.Exit(1)
+	}
+	return
+}
+
+type Command int
+
+const (
+	commandEval = iota
+	commandFmt  = iota
+)
+
+type config struct {
+	cmd            Command
+	inputFiles     []string
+	outputFile     string
+	filenameIsCode bool
+
+	// commandEval flags
+	evalMulti          bool
+	evalStream         bool
+	evalMultiOutputDir string
+	evalJpath          []string
+
+	// commandFmt flags
+	// commandFmt is currently unsupported.
+}
+
+func makeConfig() config {
+	return config{
+		cmd:            commandEval,
+		filenameIsCode: false,
+		evalMulti:      false,
+		evalStream:     false,
+		evalJpath:      []string{},
+	}
+}
+
+func getVarVal(s string) (string, string, error) {
 	parts := strings.SplitN(s, "=", 2)
 	name := parts[0]
 	if len(parts) == 1 {
@@ -45,6 +170,324 @@ func getVar(s string) (string, string, error) {
 	}
 }
 
+func getVarFile(s string) (string, string, error) {
+	parts := strings.SplitN(s, "=", 2)
+	name := parts[0]
+	if len(parts) == 1 {
+		return "", "", fmt.Errorf("ERROR: argument not in form <var>=<file> \"%s\".", s)
+	} else {
+		b, err := ioutil.ReadFile(parts[1])
+		if err != nil {
+			return "", "", err
+		}
+		return name, string(b), nil
+	}
+}
+
+type processArgsStatus = int
+const (
+	processArgsStatusContinue = iota
+	processArgsStatusSuccessUsage = iota
+	processArgsStatusFailureUsage = iota
+	processArgsStatusSuccess = iota
+	processArgsStatusFailure = iota
+)
+
+func processArgs(givenArgs []string, config *config, vm *jsonnet.VM) (processArgsStatus, error) {
+	args := simplifyArgs(givenArgs)
+	remainingArgs := make([]string, 0, 0)
+	i := 0
+	if len(args) > 0 && args[i] == "fmt" {
+		config.cmd = commandFmt
+		i++
+	} else if len(args) > 0 && args[i] == "eval" {
+		config.cmd = commandEval
+		i++
+	}
+
+	for ; i < len(args); i++ {
+		arg := args[i]
+		if arg == "-h" || arg == "--help" {
+			return processArgsStatusSuccessUsage, nil
+		} else if arg == "-v" || arg == "--version" {
+			version(os.Stdout)
+			return processArgsStatusSuccess, nil
+		} else if arg == "-e" || arg == "--exec" {
+			config.filenameIsCode = true
+		} else if arg == "-o" || arg == "--exec" {
+			outputFile := nextArg(&i, args)
+			if len(outputFile) == 0 {
+				return processArgsStatusFailure, fmt.Errorf("ERROR: -o argument was empty string")
+			}
+			config.outputFile = outputFile
+		} else if arg == "--" {
+			// All subsequent args are not options.
+			i++
+			for ; i < len(args); i++ {
+				remainingArgs = append(remainingArgs, args[i])
+			}
+			break
+		} else if config.cmd == commandEval {
+			if arg == "-s" || arg == "--max-stack" {
+				l := safeStrToInt(nextArg(&i, args))
+				if l < 1 {
+					return processArgsStatusFailure, fmt.Errorf("ERROR: Invalid --max-stack value: %d", l)
+				}
+				vm.MaxStack = l
+			} else if arg == "-J" || arg == "--jpath" {
+				dir := nextArg(&i, args)
+				if len(dir) == 0 {
+					return processArgsStatusFailure, fmt.Errorf("ERROR: -J argument was empty string")
+				}
+				if dir[len(dir)-1] != '/' {
+					dir += "/"
+				}
+				config.evalJpath = append(config.evalJpath, dir)
+			} else if arg == "-V" || arg == "--ext-str" {
+				next := nextArg(&i, args)
+				name, content, err := getVarVal(next)
+				if err != nil {
+					return processArgsStatusFailure, err
+				}
+				vm.ExtVar(name, content)
+			} else if arg == "--ext-str-file" {
+				next := nextArg(&i, args)
+				name, content, err := getVarFile(next)
+				if err != nil {
+					return processArgsStatusFailure, err
+				}
+				vm.ExtVar(name, content)
+			} else if arg == "--ext-code" {
+				next := nextArg(&i, args)
+				name, content, err := getVarVal(next)
+				if err != nil {
+					return processArgsStatusFailure, err
+				}
+				vm.ExtCode(name, content)
+			} else if arg == "--ext-code-file" {
+				next := nextArg(&i, args)
+				name, content, err := getVarFile(next)
+				if err != nil {
+					return processArgsStatusFailure, err
+				}
+				vm.ExtCode(name, content)
+			} else if arg == "-A" || arg == "--tla-str" {
+				next := nextArg(&i, args)
+				name, content, err := getVarVal(next)
+				if err != nil {
+					return processArgsStatusFailure, err
+				}
+				vm.TLAVar(name, content)
+			} else if arg == "--tla-str-file" {
+				next := nextArg(&i, args)
+				name, content, err := getVarFile(next)
+				if err != nil {
+					return processArgsStatusFailure, err
+				}
+				vm.TLAVar(name, content)
+			} else if arg == "--tla-code" {
+				next := nextArg(&i, args)
+				name, content, err := getVarVal(next)
+				if err != nil {
+					return processArgsStatusFailure, err
+				}
+				vm.TLACode(name, content)
+			} else if arg == "--tla-code-file" {
+				next := nextArg(&i, args)
+				name, content, err := getVarFile(next)
+				if err != nil {
+					return processArgsStatusFailure, err
+				}
+				vm.TLACode(name, content)
+			} else if arg == "-t" || arg == "--max-trace" {
+				l := safeStrToInt(nextArg(&i, args))
+				if l < 0 {
+					return processArgsStatusFailure, fmt.Errorf("ERROR: Invalid --max-trace value: %d", l)
+				}
+				vm.ErrorFormatter.MaxStackTraceSize = l
+			} else if arg == "-m" || arg == "--multi" {
+				config.evalMulti = true
+				outputDir := nextArg(&i, args)
+				if len(outputDir) == 0 {
+					return processArgsStatusFailure, fmt.Errorf("ERROR: -m argument was empty string")
+				}
+				if outputDir[len(outputDir)-1] != '/' {
+					outputDir += "/"
+				}
+				config.evalMultiOutputDir = outputDir
+			} else if arg == "-y" || arg == "--yaml-stream" {
+				config.evalStream = true
+			} else if arg == "-S" || arg == "--string" {
+				vm.StringOutput = true
+			} else if len(arg) > 1 && arg[0] == '-' {
+				return processArgsStatusFailure, fmt.Errorf("ERROR: Unrecognized argument: %s", arg)
+			} else {
+				remainingArgs = append(remainingArgs, arg)
+			}
+
+		} else {
+			return processArgsStatusFailure, fmt.Errorf("The Go implementation currently does not support jsonnet fmt.")
+		}
+	}
+
+	want := "filename"
+	if config.filenameIsCode {
+		want = "code"
+	}
+	if len(remainingArgs) == 0 {
+		return processArgsStatusFailureUsage, fmt.Errorf("ERROR: Must give %s", want)
+	}
+
+	// TODO(dcunnin): Formatter allows multiple files in test and in-place mode.
+	multipleFilesAllowed := false
+
+	if !multipleFilesAllowed {
+		if len(remainingArgs) > 1 {
+			return processArgsStatusFailure, fmt.Errorf("ERROR: Only one %s is allowed", want)
+		}
+	}
+
+	config.inputFiles = remainingArgs
+	return processArgsStatusContinue, nil
+}
+
+// readInput gets Jsonnet code from the given place (file, commandline, stdin).
+// It also updates the given filename to <stdin> or <cmdline> if it wasn't a real filename.
+func readInput(config config, filename *string) (input string, err error) {
+	if config.filenameIsCode {
+		input, err = *filename, nil
+		*filename = "<cmdline>"
+	} else if *filename == "-" {
+		var bytes []byte
+		bytes, err = ioutil.ReadAll(os.Stdin)
+		input = string(bytes)
+		*filename = "<stdin>"
+	} else {
+		var bytes []byte
+		bytes, err = ioutil.ReadFile(*filename)
+		input = string(bytes)
+	}
+	return
+}
+
+func writeMultiOutputFiles(output map[string]string, outputDir, outputFile string) error {
+	// If multiple file output is used, then iterate over each string from
+	// the sequence of strings returned by jsonnet_evaluate_snippet_multi,
+	// construct pairs of filename and content, and write each output file.
+
+	var manifest *os.File
+
+	if outputFile == "" {
+		manifest = os.Stdout
+	} else {
+		var err error
+		manifest, err = os.Create(outputFile)
+		if err != nil {
+			return err
+		}
+		defer manifest.Close()
+	}
+
+	// Iterate through the map in order.
+	keys := make([]string, 0, len(output))
+	for k, _ := range output {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+	for _, key := range keys {
+		newContent := output[key]
+		filename := outputDir + key
+
+		_, err := manifest.WriteString(filename)
+		if err != nil {
+			return err
+		}
+
+		_, err = manifest.WriteString("\n")
+		if err != nil {
+			return err
+		}
+
+		if _, err := os.Stat(filename); !os.IsNotExist(err) {
+			existingContent, err := ioutil.ReadFile(filename)
+			if err != nil {
+				return err
+			}
+			if string(existingContent) == newContent {
+				// Do not bump the timestamp on the file if its content is
+				// the same. This may trigger other tools (e.g. make) to do
+				// unnecessary work.
+				continue
+			}
+		}
+
+		f, err := os.Create(filename)
+		if err != nil {
+			return err
+		}
+		defer f.Close()
+
+		_, err = f.WriteString(newContent)
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// writeOutputStream writes the output as a YAML stream.
+func writeOutputStream(output []string, outputFile string) error {
+	var f *os.File
+
+	if outputFile == "" {
+		f = os.Stdout
+	} else {
+		var err error
+		f, err = os.Create(outputFile)
+		if err != nil {
+			return err
+		}
+		defer f.Close()
+	}
+
+	for _, doc := range output {
+		_, err := f.WriteString("---\n")
+		if err != nil {
+			return err
+		}
+		_, err = f.WriteString(doc)
+		if err != nil {
+			return err
+		}
+	}
+
+	if len(output) > 0 {
+		_, err := f.WriteString("...\n")
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func writeOutputFile(output string, outputFile string) error {
+	if outputFile == "" {
+		fmt.Print(output)
+		return nil
+	}
+
+	f, err := os.Create(outputFile)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	_, err = f.WriteString(output)
+	return err
+}
+
 func main() {
 	// https://blog.golang.org/profiling-go-programs
 	var cpuprofile = os.Getenv("JSONNET_CPU_PROFILE")
@@ -57,62 +500,102 @@ func main() {
 		defer pprof.StopCPUProfile()
 	}
 
-	// TODO(sbarzowski) Be consistent about error codes with C++ maybe
-	var filename string
-
 	vm := jsonnet.MakeVM()
-	for i := 1; i < len(os.Args); i++ {
-		arg := os.Args[i]
-		switch arg {
-		case "--tla-str":
-			i++
-			name, content, err := getVar(os.Args[i])
-			if err != nil {
-				fmt.Fprintln(os.Stderr, err.Error())
-				os.Exit(1)
-			}
-			vm.TLAVar(name, content)
-		case "--tla-code":
-			i++
-			name, content, err := getVar(os.Args[i])
-			if err != nil {
-				fmt.Fprintln(os.Stderr, err.Error())
-				os.Exit(1)
-			}
-			vm.TLACode(name, content)
-		case "--ext-code":
-			i++
-			name, content, err := getVar(os.Args[i])
-			if err != nil {
-				fmt.Fprintln(os.Stderr, err.Error())
-				os.Exit(1)
-			}
-			vm.ExtCode(name, content)
-		case "--ext-str":
-			i++
-			name, content, err := getVar(os.Args[i])
-			if err != nil {
-				fmt.Fprintln(os.Stderr, err.Error())
-				os.Exit(1)
-			}
-			vm.ExtVar(name, content)
-		default:
-			if filename != "" {
-				usage()
-				os.Exit(1)
-			}
-			filename = arg
-		}
-	}
-	snippet, err := ioutil.ReadFile(filename)
+
+	config := makeConfig()
+	status, err := processArgs(os.Args[1:], &config, vm)
 	if err != nil {
-		fmt.Fprintf(os.Stderr, "Error reading input file: %v\n", err.Error())
+		fmt.Fprintln(os.Stderr, err.Error())
+	}
+	switch status {
+	case processArgsStatusContinue:
+		break
+	case processArgsStatusSuccessUsage:
+		usage(os.Stdout)
+		os.Exit(0)
+	case processArgsStatusFailureUsage:
+		if err != nil {
+			fmt.Fprintln(os.Stderr, "")
+		}
+		usage(os.Stderr)
+		os.Exit(1)
+	case processArgsStatusSuccess:
+		os.Exit(0)
+	case processArgsStatusFailure:
 		os.Exit(1)
 	}
-	json, err := vm.EvaluateSnippet(filename, string(snippet))
-	if err != nil {
-		fmt.Fprintf(os.Stderr, "%v\n", err.Error())
-		os.Exit(2)
+
+	vm.Importer(&jsonnet.FileImporter{
+		JPaths: config.evalJpath,
+	})
+
+	if config.cmd == commandEval {
+		if len(config.inputFiles) != 1 {
+			// Should already have been caught by processArgs.
+			panic(fmt.Sprintf("Internal error: Expected a single input file."))
+		}
+		filename := config.inputFiles[0]
+		input, err := readInput(config, &filename)
+		if err != nil {
+			var op string
+			switch typedErr := err.(type) {
+			case *os.PathError:
+				op = typedErr.Op
+				err = typedErr.Err
+			}
+			if op == "open" {
+				fmt.Fprintf(os.Stderr, "Opening input file: %s: %s\n", filename, err.Error())
+			} else if op == "read" {
+				fmt.Fprintf(os.Stderr, "Reading input file: %s: %s\n", filename, err.Error())
+			} else {
+				fmt.Fprintf(os.Stderr, err.Error())
+			}
+			os.Exit(1)
+		}
+		var output string
+		var outputArray []string
+		var outputDict map[string]string
+		if config.evalMulti {
+			outputDict, err = vm.EvaluateSnippetMulti(filename, input)
+		} else if config.evalStream {
+			outputArray, err = vm.EvaluateSnippetStream(filename, input)
+		} else {
+			output, err = vm.EvaluateSnippet(filename, input)
+		}
+
+		if err != nil {
+			fmt.Fprintln(os.Stderr, err.Error())
+			os.Exit(1)
+		}
+
+		// Write output JSON.
+		if config.evalMulti {
+			err := writeMultiOutputFiles(outputDict, config.evalMultiOutputDir, config.outputFile)
+			if err != nil {
+				fmt.Fprintln(os.Stderr, err.Error())
+				os.Exit(1)
+			}
+		} else if config.evalStream {
+			err := writeOutputStream(outputArray, config.outputFile)
+			if err != nil {
+				fmt.Fprintln(os.Stderr, err.Error())
+				os.Exit(1)
+			}
+		} else {
+			err := writeOutputFile(output, config.outputFile)
+			if err != nil {
+				fmt.Fprintln(os.Stderr, err.Error())
+				os.Exit(1)
+			}
+		}
+
+	} else if config.cmd == commandFmt {
+		// Should already have been caught by processArgs.
+		panic(fmt.Sprintf("Internal error: No jsonnet fmt."))
+
+	} else {
+		panic(fmt.Sprintf("Internal error (please report this): Bad cmd value: %d\n", config.cmd))
+
 	}
-	fmt.Print(json)
+
 }
diff --git a/jsonnet/cmd_test.go b/jsonnet/cmd_test.go
new file mode 100644
index 0000000..a0caf1c
--- /dev/null
+++ b/jsonnet/cmd_test.go
@@ -0,0 +1,58 @@
+/*
+Copyright 2017 Google Inc. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package main
+
+import (
+	"testing"
+)
+
+func testEq(a, b []string) bool {
+	if a == nil && b == nil {
+		return true
+	}
+	if a == nil || b == nil {
+		return false
+	}
+	if len(a) != len(b) {
+		return false
+	}
+	for i := range a {
+		if a[i] != b[i] {
+			return false
+		}
+	}
+	return true
+}
+
+func testSimplifyAux(t *testing.T, name string, input, expected []string) {
+	t.Run(name, func(t *testing.T) {
+		got := simplifyArgs(input)
+		if !testEq(got, expected) {
+			t.Fail()
+			t.Errorf("Got %v, expected %v\n", got, expected)
+		}
+	})
+}
+
+func TestSimplifyArgs(t *testing.T) {
+	testSimplifyAux(t, "empty", []string{}, []string{})
+	testSimplifyAux(t, "-a", []string{"-a"}, []string{"-a"})
+	testSimplifyAux(t, "-a -b", []string{"-a", "-b"}, []string{"-a", "-b"})
+	testSimplifyAux(t, "-a -c -b", []string{"-a", "-c", "-b"}, []string{"-a", "-c", "-b"})
+	testSimplifyAux(t, "-abc", []string{"-abc"}, []string{"-a", "-b", "-c"})
+	testSimplifyAux(t, "-acb", []string{"-acb"}, []string{"-a", "-c", "-b"})
+}
diff --git a/main_test.go b/main_test.go
index 301c5eb..5649a64 100644
--- a/main_test.go
+++ b/main_test.go
@@ -122,12 +122,15 @@ func TestMain(t *testing.T) {
 			}
 
 			input := read(test.input)
-			output, err := vm.evaluateSnippet(test.name, string(input))
+			rawOutput, err := vm.evaluateSnippet(test.name, string(input), evalKindRegular)
+			var output string
 			if err != nil {
 				// TODO(sbarzowski) perhaps somehow mark that we are processing
 				// an error. But for now we can treat them the same.
 				output = errFormatter.format(err)
 				output += "\n"
+			} else {
+				output = rawOutput.(string)
 			}
 			if *update {
 				err := ioutil.WriteFile(test.golden, []byte(output), 0666)
@@ -169,7 +172,7 @@ type errorFormattingTest struct {
 func genericTestErrorMessage(t *testing.T, tests []errorFormattingTest, format func(RuntimeError) string) {
 	for _, test := range tests {
 		vm := MakeVM()
-		output, err := vm.evaluateSnippet(test.name, test.input)
+		rawOutput, err := vm.evaluateSnippet(test.name, test.input, evalKindRegular)
 		var errString string
 		if err != nil {
 			switch typedErr := err.(type) {
@@ -178,8 +181,8 @@ func genericTestErrorMessage(t *testing.T, tests []errorFormattingTest, format f
 			default:
 				t.Errorf("%s: unexpected error: %v", test.name, err)
 			}
-
 		}
+		output := rawOutput.(string)
 		if errString != test.errString {
 			t.Errorf("%s: error result does not match. got\n\t%+#v\nexpected\n\t%+#v",
 				test.name, errString, test.errString)
diff --git a/vm.go b/vm.go
index 62962c5..624de0b 100644
--- a/vm.go
+++ b/vm.go
@@ -31,14 +31,13 @@ import (
 // VM is the core interpreter and is the touchpoint used to parse and execute
 // Jsonnet.
 type VM struct {
-	MaxStack    int
-	MaxTrace    int // The number of lines of stack trace to display (0 for all of them).
-	ext         vmExtMap
-	tla         vmExtMap
-	nativeFuncs map[string]*NativeFunction
-	importer    Importer
-	ef          ErrorFormatter
-	StringOutput bool
+	MaxStack       int
+	ext            vmExtMap
+	tla            vmExtMap
+	nativeFuncs    map[string]*NativeFunction
+	importer       Importer
+	ErrorFormatter ErrorFormatter
+	StringOutput   bool
 }
 
 // External variable or top level argument provided before execution
@@ -55,12 +54,12 @@ type vmExtMap map[string]vmExt
 // MakeVM creates a new VM with default parameters.
 func MakeVM() *VM {
 	return &VM{
-		MaxStack:    500,
-		ext:         make(vmExtMap),
-		tla:         make(vmExtMap),
-		nativeFuncs: make(map[string]*NativeFunction),
-		ef:          ErrorFormatter{pretty: true, colorful: true, MaxStackTraceSize: 20},
-		importer:    &FileImporter{},
+		MaxStack:       500,
+		ext:            make(vmExtMap),
+		tla:            make(vmExtMap),
+		nativeFuncs:    make(map[string]*NativeFunction),
+		ErrorFormatter: ErrorFormatter{pretty: false, colorful: false, MaxStackTraceSize: 20},
+		importer:       &FileImporter{},
 	}
 }
 
@@ -89,7 +88,15 @@ func (vm *VM) Importer(i Importer) {
 	vm.importer = i
 }
 
-func (vm *VM) evaluateSnippet(filename string, snippet string) (output string, err error) {
+type evalKind = int
+
+const (
+	evalKindRegular = iota
+	evalKindMulti   = iota
+	evalKindStream  = iota
+)
+
+func (vm *VM) evaluateSnippet(filename string, snippet string, kind evalKind) (output interface{}, err error) {
 	defer func() {
 		if r := recover(); r != nil {
 			err = fmt.Errorf("(CRASH) %v\n%s", r, debug.Stack())
@@ -99,7 +106,14 @@ func (vm *VM) evaluateSnippet(filename string, snippet string) (output string, e
 	if err != nil {
 		return "", err
 	}
-	output, err = evaluate(node, vm.ext, vm.tla, vm.nativeFuncs, vm.MaxStack, vm.importer, vm.StringOutput)
+	switch kind {
+	case evalKindRegular:
+		output, err = evaluate(node, vm.ext, vm.tla, vm.nativeFuncs, vm.MaxStack, vm.importer, vm.StringOutput)
+	case evalKindMulti:
+		output, err = evaluateMulti(node, vm.ext, vm.tla, vm.nativeFuncs, vm.MaxStack, vm.importer, vm.StringOutput)
+	case evalKindStream:
+		output, err = evaluateStream(node, vm.ext, vm.tla, vm.nativeFuncs, vm.MaxStack, vm.importer)
+	}
 	if err != nil {
 		return "", err
 	}
@@ -116,11 +130,38 @@ func (vm *VM) NativeFunction(f *NativeFunction) {
 //
 // The filename parameter is only used for error messages.
 func (vm *VM) EvaluateSnippet(filename string, snippet string) (json string, formattedErr error) {
-	json, err := vm.evaluateSnippet(filename, snippet)
+	output, err := vm.evaluateSnippet(filename, snippet, evalKindRegular)
 	if err != nil {
-		return "", errors.New(vm.ef.format(err))
+		return "", errors.New(vm.ErrorFormatter.format(err))
 	}
-	return json, nil
+	json = output.(string)
+	return
+}
+
+// EvaluateSnippetStream evaluates a string containing Jsonnet code to an array.
+// The array is returned as an array of JSON strings.
+//
+// The filename parameter is only used for error messages.
+func (vm *VM) EvaluateSnippetStream(filename string, snippet string) (docs []string, formattedErr error) {
+	output, err := vm.evaluateSnippet(filename, snippet, evalKindStream)
+	if err != nil {
+		return nil, errors.New(vm.ErrorFormatter.format(err))
+	}
+	docs = output.([]string)
+	return
+}
+
+// EvaluateSnippetStream evaluates a string containing Jsonnet code to an array.
+// The array is returned as an array of JSON strings.
+//
+// The filename parameter is only used for error messages.
+func (vm *VM) EvaluateSnippetMulti(filename string, snippet string) (files map[string]string, formattedErr error) {
+	output, err := vm.evaluateSnippet(filename, snippet, evalKindMulti)
+	if err != nil {
+		return nil, errors.New(vm.ErrorFormatter.format(err))
+	}
+	files = output.(map[string]string)
+	return
 }
 
 func snippetToAST(filename string, snippet string) (ast.Node, error) {