执行npm run dev就失败了

vue 安装成功，项目创建也成功了，执行npm run dev就失败了，失败结果

> test1@1.0.0 dev /Users/ann/test1

> webpack-dev-server --inline --progress --config build/webpack.dev.conf.js

sh: webpack-dev-server: command not found

npm ERR! file sh

npm ERR! code ELIFECYCLE

npm ERR! errno ENOENT

npm ERR! syscall spawn

npm ERR! test1@1.0.0 dev: `webpack-dev-server --inline --progress --config build/webpack.dev.conf.js`

npm ERR! spawn ENOENT

npm ERR! 

npm ERR! Failed at the test1@1.0.0 dev script.

npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm WARN Local package.json exists, but node_modules missing, did you mean to install?

npm ERR! A complete log of this run can be found in:

npm ERR!     /Users/ann/.npm/_logs/2018-10-28T08_11_37_746Z-debug.log

，npm -v也显示版本的。

有时候执行其他命令会出现command not found，比如我想用brew安装node就会出现-bash: brew: command not found。

我是mac电脑，请求高手老师帮忙，困扰好多天了，万分感谢