Add Get{Flag,Arg,Command}.

args.go

@@ -14,6 +14,19 @@ func (a *argGroup) have() bool {
 	return len(a.args) > 0
 }
 
+// GetArg gets an argument definition.
+//
+// This allows existing arguments to be modified after definition but before parsing. Useful for
+// modular applications.
+func (a *argGroup) GetArg(name string) *ArgClause {
+	for _, arg := range a.args {
+		if arg.name == name {
+			return arg
+		}
+	}
+	return nil
+}
+
 func (a *argGroup) Arg(name, help string) *ArgClause {
 	arg := newArg(name, help)
 	a.args = append(a.args, arg)

cmd.go

@@ -21,6 +21,14 @@ func (c *cmdGroup) defaultSubcommand() *CmdClause {
 	return nil
 }
 
+// GetArg gets a command definition.
+//
+// This allows existing commands to be modified after definition but before parsing. Useful for
+// modular applications.
+func (c *cmdGroup) GetCommand(name string) *CmdClause {
+	return c.commands[name]
+}
+
 func newCmdGroup(app *Application) *cmdGroup {
 	return &cmdGroup{
 		app:      app,

flags.go

@@ -19,6 +19,14 @@ func newFlagGroup() *flagGroup {
 	}
 }
 
+// GetFlag a flag definition.
+//
+// This allows existing flags to be modified after definition but before parsing. Useful for
+// modular applications.
+func (f *flagGroup) GetFlag(name string) *FlagClause {
+	return f.long[name]
+}
+
 // Flag defines a new flag with the given long name and help.
 func (f *flagGroup) Flag(name, help string) *FlagClause {
 	flag := newFlag(name, help)

flags_test.go

@@ -144,3 +144,15 @@ func TestDuplicateLongFlag(t *testing.T) {
 	_, err := app.Parse([]string{})
 	assert.Error(t, err)
 }
+
+func TestGetFlagAndOverrideDefault(t *testing.T) {
+	app := newTestApp()
+	a := app.Flag("a", "").Default("default").String()
+	_, err := app.Parse([]string{})
+	assert.NoError(t, err)
+	assert.Equal(t, "default", *a)
+	app.GetFlag("a").Default("new")
+	_, err = app.Parse([]string{})
+	assert.NoError(t, err)
+	assert.Equal(t, "new", *a)
+}