How does nodejs read environment variables set in command line?

Question

I feel like asking a silly question but I have googled it for a while and can't find a satisfying answer. SO doesn't such discussion either, only How to set NODE_ENV to production/development in OS X and How can I set NODE_ENV=production on Windows?

To run a command after another in one line we normally join them by ; ( or &&)

So I had assumed I should run command like this PORT=3000 ; node server.js or export PORT=3000; node server.js , just like PORT=3000 ; echo $PORT

But we just put a space between PORT=3000 node server.js (without ; or &&) and PORT is read into process.env.PORT. How does shell make nodejs get environment variables? It will be better if someone can show nodejs codes.

----- update ------

The reason I was puzzled with this shell syntax (according to my limited knowledge) is that I think the general format for a Unix command line is

command options(s) filename(s)

The space in between is used to separate command from option and filename. So how can it be used to separate 2 commands as well?

Why do you think that it is only available in node?? Do PORT=3000 echo Qiulang — bugwheels94
– bugwheels94, Commented Feb 12, 2018 at 3:16
I assume you were trying to help but my understanding is that putting a space between two commands just does not work. And that is my question. — Qiulang
– Qiulang, Commented Feb 12, 2018 at 4:37
I am saying it is not Nodejs specific so u won't get any Nodejs code. Not sure, but it is part of shell syntax — bugwheels94
– bugwheels94, Commented Feb 12, 2018 at 4:44
@Qiulang dude, i think it is valid syntax, you can try with PORT=1000 echo 'hello' && echo 'world', if first half failed everything after && won't get executed. — Allen
– Allen, Commented Feb 12, 2018 at 4:46
@Xlee I will suggest to you try PORT=1000 echo $PORT and you can see the result is empty. i.e. PORT is not set — Qiulang
– Qiulang, Commented Feb 12, 2018 at 4:48

Qiulang · Accepted Answer · 2020-03-01 12:37:52Z

1

I checked nodejs document and found the answer https://nodejs.org/api/process.html#process_process_env

So it is environ, not 2 separated commands,

Bourne-style shells support the syntax
       NAME=value command
to create an environment variable definition only in the scope of the process that executes command.

Or as bash manual 3.7.4 explained.

For python, it is os.environ['NAME']

This is also the reason why it won't work on windows: How can I set NODE_ENV=production on Windows?

Notes for Windows users, as a comment there by daw "set NODE_ENV=production && " adds a trailing space to the variable and don't use single/double quote.

I feel quite embarrassed that I almost wanted to delete my question. I keep it here in case someone else may also have this doubt. Or someone else can further explain environ or how node read it into process.env object.

edited Mar 1, 2020 at 12:37

answered Feb 12, 2018 at 10:32

Qiulang

12.8k22 gold badges99 silver badges158 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

How does nodejs read environment variables set in command line?

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related