I was having the same issue when tried with the syntax "ng new " and solved that simply by updating the existing node version from 5.x.x to 8.x.x. After successful updation of node, the syntax worked perfectly for me. Please update the existing version of node. As it is clearly mentioned in angular documentation that these commands require the node version >= 6.9.x. For reference please check https://angular.io/guide/quickstart. It clearly states "Verify that you are running at least node 6.9.x and npm 3.x.x by running node -v and npm -v in a terminal/console window. Older versions produce errors, but newer versions are fine".

PATH环境变量需要更新，添加如下PATH，

C:\Users\xyzname\AppData\Roaming\npm\node_modules\@angular\cli\bin

因为ng文件在bin文件夹中，一旦添加了这个，ng肯定会被识别出来

设置路径= % %路径;C: \ \ \ AppData \ \ npm漫游用户

在尝试更新Windows 7 (x64)上的PATH变量之前，运行CMD控制台AS ADMINISTRATOR和ng命令对我有用，这也适用于VISUAL STUDIO CODE控制台。

它为我工作在CMD控制台/ VS CODE

对我来说，PATH环境变量有问题。我删除了所有与npm相关的路径，并在path的开头添加了这个文件夹:

c:\Users\<your-user-name>\AppData\Roaming\npm\

确保你有;之间的路径。

将C:\Users\DELL\AppData\Roaming\npm添加到系统变量路径对我来说很有效。请找到相应的“npm”文件路径

另外，检查是否已经将angular-cli\bin路径添加到path变量中。