build:server & export:server commands are not working

[skptricks]

getting below error message while executing below commads : yarn build:server yarn export:server

D:\sumitprojects\NextSimpleStarter>yarn export yarn run v1.17.3 $ npm run build:server && npm run export:server

[email protected] build:server D:\sumitprojects\NextSimpleStarter NEXT_TARGET=server next build

'NEXT_TARGET' is not recognized as an internal or external command, operable program or batch file. npm ERR! code ELIFECYCLE npm ERR! errno 1 npm ERR! [email protected] build:server: NEXT_TARGET=server next build npm ERR! Exit status 1 npm ERR! npm ERR! Failed at the [email protected] build:server script. npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in: npm ERR! C:\Users\Acer-sumit\AppData\Roaming\npm-cache_logs\2019-08-26T19_52_15_967Z-debug.log error Command failed with exit code 1. info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.