Verify that the subcommand found is a complete command

cli.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"regexp"
 	"sort"
 	"strings"
 	"sync"
@@ -405,16 +406,24 @@ func (c *CLI) processArgs() {
 		}
 
 		// If we didn't find a subcommand yet and this is the first non-flag
-		// argument, then this is our subcommand. j
+		// argument, then this is our subcommand.
 		if c.subcommand == "" && arg != "" && arg[0] != '-' {
 			c.subcommand = arg
 			if c.commandNested {
 				// Nested CLI, the subcommand is actually the entire
 				// arg list up to a flag that is still a valid subcommand.
-				k, _, ok := c.commandTree.LongestPrefix(strings.Join(c.Args[i:], " "))
+				searchKey := strings.Join(c.Args[i:], " ")
+				k, _, ok := c.commandTree.LongestPrefix(searchKey)
 				if ok {
-					c.subcommand = k
-					i += strings.Count(k, " ")
+					// k could be a prefix that doesn't contain the full
+					// command such as "foo" instead of "foobar", so we
+					// need to verify that we have an entire key. To do that,
+					// we look for an ending in a space or an end of string.
+					reVerify := regexp.MustCompile(regexp.QuoteMeta(k) + `( |$)`)
+					if reVerify.MatchString(searchKey) {
+						c.subcommand = k
+						i += strings.Count(k, " ")
+					}
 				}
 			}
 

cli_test.go

@@ -119,6 +119,37 @@ func TestCLIRun_blank(t *testing.T) {
 	}
 }
 
+func TestCLIRun_prefix(t *testing.T) {
+	buf := new(bytes.Buffer)
+	command := new(MockCommand)
+	cli := &CLI{
+		Args: []string{"foobar"},
+		Commands: map[string]CommandFactory{
+			"foo": func() (Command, error) {
+				return command, nil
+			},
+
+			"foo bar": func() (Command, error) {
+				return command, nil
+			},
+		},
+		HelpWriter: buf,
+	}
+
+	exitCode, err := cli.Run()
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	if exitCode != 1 {
+		t.Fatalf("bad: %d", exitCode)
+	}
+
+	if command.RunCalled {
+		t.Fatalf("run should not be called")
+	}
+}
+
 func TestCLIRun_default(t *testing.T) {
 	commandBar := new(MockCommand)
 	commandBar.RunResult = 42