add GetArgvAt method for Context. see issue #38

_examples/027-global-option/main.go

@@ -47,17 +47,29 @@ var sub = &cli.Command{
 	Desc: "subcommand",
 	Argv: func() interface{} { return new(subT) },
 	Fn: func(ctx *cli.Context) error {
-		ctx.JSON(ctx.RootArgv())
-		ctx.JSON(ctx.Argv())
-		ctx.String("\n")
+		ctx.JSONln(ctx.RootArgv())
+		ctx.JSONln(ctx.Argv())
 
 		var argv = &subT{}
 		var parentArgv = &rootT{}
 		if err := ctx.GetArgvList(argv, parentArgv); err != nil {
 			return err
 		}
-		ctx.JSON(parentArgv)
-		ctx.JSON(argv)
+		ctx.JSONln(parentArgv)
+		ctx.JSONln(argv)
+
+		argv = &subT{}
+		if err := ctx.GetArgvAt(argv, 0); err != nil {
+			return err
+		}
+		ctx.JSONln(argv)
+
+		parentArgv = &rootT{}
+		if err := ctx.GetArgvAt(parentArgv, 1); err != nil {
+			return err
+		}
+		ctx.JSONln(parentArgv)
+
 		return nil
 	},
 }

_examples/027-global-option/run.sh

@@ -33,15 +33,15 @@ echo ===run sub command
 echo
 
 echo =case 1: read from file
-./app sub
+./app sub -w xxx
 echo
 
 echo =case 2: read from ENV variables
-HOST=10.0.0.1 ./app sub
+HOST=10.0.0.1 ./app sub -w xxx
 echo
 
 echo =case 3: read from command line
-HOST=10.0.0.1 ./app sub -H 168.0.0.1
+HOST=10.0.0.1 ./app sub -H 168.0.0.1 -w xxx
 echo
 
 echo

context.go

@@ -3,6 +3,7 @@ package cli
 import (
 	"bytes"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"net/http"
@@ -143,6 +144,27 @@ func (ctx *Context) GetArgvList(curr interface{}, parents ...interface{}) error
 	return nil
 }
 
+func (ctx *Context) GetArgvAt(argv interface{}, i int) error {
+	if isEmptyArgvList(ctx.argvList) {
+		return argvError{isEmpty: true}
+	}
+	if argv == nil {
+		return errors.New("argv is nil")
+	}
+	if i >= len(ctx.argvList) {
+		return argvError{isOutOfRange: true}
+	}
+	if ctx.argvList[i] == nil {
+		return argvError{ith: i, msg: "source is nil"}
+	}
+
+	buf := bytes.NewBufferString("")
+	if err := json.NewEncoder(buf).Encode(ctx.argvList[i]); err != nil {
+		return err
+	}
+	return json.NewDecoder(buf).Decode(argv)
+}
+
 // IsSet determins whether `flag` is set
 func (ctx *Context) IsSet(flag string, aliasFlags ...string) bool {
 	fl, ok := ctx.flagSet.flagMap[flag]