Yii 2 installation error

I am installing new yii2 project.I have already installed the controller .but when i run following command in terminal

php composer.phar create-project --stability=dev yiisoft/yii2-app-basic my_yii2_trial

and for

php composer.phar create-project yiisoft/yii2-app-basic basic

for both this command Its showing error that,

[InvalidArgumentException]                                            
  Could not find package yiisoft/yii2-app-basic with stability stable. 

Please help.