webpack打包 ERROR in multi ./appjs/main.js public/webpack.js

webpack -v
4.1.1


运行如下命令，报错
webpack appjs/main.js public/webpack.js

D:\idea_workspace\idea_test\app>
webpack appjs/main.js public/webpack.js
Hash: 7d64667dd2038512ab77
Version: webpack 4.1.1
Time: 81ms
Built at: 2018-3-20 12:25:20
1 asset
Entrypoint main = main.js
   [0] ./appjs/config.json 33 bytes {0} [built]
   [1] ./appjs/work.js 71 bytes {0} [built]
   [2] ./appjs/main.js 20 bytes {0} [built]
   [3] multi ./appjs/main.js public/webpack.js 40 bytes {0} [built]

WARNING in configuration
The 'mode' option has not been set. Set 'mode' option to 'development' or 'production' to enable defaults for this environment.


ERROR in multi ./appjs/main.js public/webpack.js
Module not found: Error: Can't resolve 'public/webpack.js' in 'D:\idea_workspace\idea_test\app'
@ multi ./appjs/main.js public/webpack.js



解决方法：webpack appjs/main.js -o public/webpack.js