process.env in Node.js

process | Node.js
http://nodejs.cn/api/process.html
process is a global  object
http://nodejs.cn/api/process.html#process_process_env

demo in script：
if (process.env.NODE_ENV === 'production') {
module.exports = require('./prod.js')
} else {
module.exports = require('./dev.js')
}
input "node" line commend
node
> process.env  // show value

On Windows: set test=testValue
on OS X or Linux: export test=testValue
In js file
process.env.test= 'dev';
package.json：
"scripts": {
"start": "set test=dev && node app.js"
}

------------------------
Windows environment variant
cmd
> set test-env   // exit
set test-env=production
set path=%path%;C:\web;C:\Tools
set test-env=

my computer -> property -> advance -> environment variant...
----------------------
Linux
echo $test-env     //check value of test-env
// set value of test-env
export test-env=production
# attach value
export path=$path:/home/download:/usr/local/
#delete value of test-env
unset test-env
#show all variants
env

# for all users
vim /etc/profile
# only current user
vim ~/.bash_profile
export path=$path:/home/download:/usr/local/
export test-env= product

# edit  /etc/profile , then  to run the following
source /etc/profile
# edit ~/.bash_profile , then to run the following
source ~/.bash_profile
-------------------

linux
export NODE_ENV=dev
https://www.npmjs.com/package/request
const request = require('request');
reference: http://www.ssqhm.com  https://www.cnblogs.com/zdz8207/p/nodejs-process-env.html
https://segmentfault.com/a/1190000011683741