diff --git a/cmd/gomtree/main.go b/cmd/gomtree/main.go
index 3551bcc..d131c87 100644
--- a/cmd/gomtree/main.go
+++ b/cmd/gomtree/main.go
@@ -1,39 +1,118 @@
 package main
 
 import (
-	"bufio"
 	"flag"
 	"fmt"
 	"log"
 	"os"
 	"strings"
+
+	mtree "../.."
+)
+
+var (
+	flCreate       = flag.Bool("c", false, "create a directory hierarchy spec")
+	flFile         = flag.String("f", "", "directory hierarchy spec to validate")
+	flPath         = flag.String("p", "", "root path that the hierarchy spec is relative to")
+	flAddKeywords  = flag.String("K", "", "Add the specified (delimited by comma or space) keywords to the current set of keywords")
+	flUseKeywords  = flag.String("k", "", "Use the specified (delimited by comma or space) keywords as the current set of keywords")
+	flListKeywords = flag.Bool("l", false, "List the keywords available")
 )
 
 func main() {
 	flag.Parse()
-	_ = mtree.DirectoryHierarchy{}
-	for _, file := range flag.Args() {
-		func() {
-			fh, err := os.Open(file)
-			if err != nil {
-				log.Println(err)
-				return
-			}
-			defer fh.Close()
 
-			s := bufio.NewScanner(fh)
-			for s.Scan() {
-				str := s.Text()
-				switch {
-				case strings.HasPrefix(str, "#"):
-					continue
-				default:
-				}
-				fmt.Printf("%q\n", str)
+	// so that defers cleanly exec
+	var isErr bool
+	defer func() {
+		if isErr {
+			os.Exit(1)
+		}
+	}()
+
+	// -l
+	if *flListKeywords {
+		fmt.Println("Available keywords:")
+		for k := range mtree.KeywordFuncs {
+			if inSlice(k, mtree.DefaultKeywords) {
+				fmt.Println(" ", k, " (default)")
+			} else {
+				fmt.Println(" ", k)
 			}
-			if err := s.Err(); err != nil {
-				log.Println("ERROR:", err)
-			}
-		}()
+		}
+		return
+	}
+
+	var currentKeywords []string
+	// -k <keywords>
+	if *flUseKeywords != "" {
+		currentKeywords = splitKeywordsArg(*flUseKeywords)
+	} else {
+		currentKeywords = mtree.DefaultKeywords[:]
+	}
+	// -K <keywords>
+	if *flAddKeywords != "" {
+		currentKeywords = append(currentKeywords, splitKeywordsArg(*flAddKeywords)...)
+	}
+
+	// -f <file>
+	var dh *mtree.DirectoryHierarchy
+	if *flFile != "" && !*flCreate {
+		// load the hierarchy, if we're not creating a new spec
+		fh, err := os.Open(*flFile)
+		if err != nil {
+			log.Println(err)
+			isErr = true
+			return
+		}
+		dh, err = mtree.ParseSpec(fh)
+		fh.Close()
+		if err != nil {
+			log.Println(err)
+			isErr = true
+			return
+		}
+	}
+
+	// -p <path>
+	var rootPath string = "."
+	if *flPath != "" {
+		rootPath = *flPath
+	}
+
+	// -c
+	if *flCreate {
+		// create a directory hierarchy
+		dh, err := mtree.Walk(rootPath, nil, currentKeywords)
+		if err != nil {
+			log.Println(err)
+			isErr = true
+			return
+		}
+		dh.WriteTo(os.Stdout)
+	} else {
+		// else this is a validation
+		res, err := mtree.Check(rootPath, dh)
+		if err != nil {
+			log.Println(err)
+			isErr = true
+			return
+		}
+		if res != nil {
+			fmt.Printf("%#v\n", res)
+		}
 	}
 }
+
+func splitKeywordsArg(str string) []string {
+	return strings.Fields(strings.Replace(str, ",", " ", -1))
+}
+
+func inSlice(a string, list []string) bool {
+	for _, b := range list {
+		if b == a {
+			return true
+		}
+	}
+	return false
+}