How can I set an environmental variable using script in node.js?

I have script that give me deployed solidity contract address and i have to use it in my .env file (i am using dotenv module).

I try to find out way to update or add that newly generated contract value to the .env file but can't get much.

is there any way so i can update or add value that i get from script to .env file?

How can I set an environmental variable using script in node.js?

I have script that give me deployed solidity contract address and i have to use it in my .env file (i am using dotenv module).

I try to find out way to update or add that newly generated contract value to the .env file but can't get much.

is there any way so i can update or add value that i get from script to .env file?

• javascript
• node.js
• solidity

• can you simply write to the .env file? – Jaromanda X Commented Apr 13, 2018 at 6:55
• @JaromandaX , i want script to write that – Jignesh Aakoliya Commented Apr 13, 2018 at 6:56
• 1 do you know how to write to a file in node? – Jaromanda X Commented Apr 13, 2018 at 6:58
• @JaromandaX i know about write and read using fs. but if value exist than update that key=value is problem – Jignesh Aakoliya Commented Apr 13, 2018 at 7:00

3 Answers 3

I don't quite get what you are trying to do, but usually environment variables are set for runtime. You shouldn't update env variables when your app is running.

For dotenv (https://www.npmjs./package/dotenv), you create a file .env put some variables there:

FOO=bar
BAZ=bob

Then require and use your .env file

require('dotenv').config();

console.log(process.env.FOO);
// bar

Without any libraries you can also provide env variables directly to node script like this

USER_ID=abc USER_PASSWORD=def node app.js

And again use it like:

console.log(process.env.USER_ID);
// abc

You should not include the .env in your version control repository (add it to your .gitignore file).

In JavaScript you can use either environment variable, or if it is not defined, add something else for example:

const yourVariable = process.env.yourVariable || 'Get stuff done';

If the process.env.yourVariable is not defined the app will use "Get stuff done" string instead.

And what I think you are asking for is something that I bet you shouldn't do with env variables. Anyways this is a hack I found, and probably should work. You can set new env variable on runtime like this (I have not tried) as environment variables are intended to be set from the outside of the code, not inside. However there might be use cases where you want to use this, launching child processes or tests or what ever.

process.env['NODE_ENV'] = 'production';

If you want to write the values in .env during runtime, you need to read and append to the file which is whole new story. Good luck.

Please follow this link https://www.npmjs./package/dotenv ,it gives a clear way to integrate the environment variables by use dotenv npm package.

You can do something like this:

     fs.readFile("./.env", 'utf8', function (err, data) {
          if (err) {
            return console.log(err);
          };
          let envVar = process.env.envVar ;
          let re = new RegExp(envVar , "g");
          let result = data.replace(re, `${newEnvVarValue}`);
          console.log(result)

          fs.writeFile("./.env", result, 'utf8', function (err) {
            if (err) return console.log(err);
          });