Change default port behavior

[ThomasG77]

Is this a bug report?

Yes

Have you read the Contributing Guidelines?

Yes

Environment

• Ubuntu 16.04 64 bits
• Node 8.4.0
• npm 5.6.0

Steps to Reproduce

When I run npm run start from step 4 of https://docusaurus.io/docs/en/site-preparation.html#verifying-installation, I encounter following message (as I have another server running on 3000)

Checking if port 3000 is free...
Port 3000 is in use

I tried to do PORT=3001 npm run start and it fails.

I've seen that I can set port using --port 3001 at https://github.com/facebook/Docusaurus/blob/master/lib/start-server.js#L34

Expected Behavior

I would expect that if port 3000 is not available, it would automatically switch to PORT number + 1 (like http-server does)
I would also expect PORT=3001 npm run start should not fail.

Actual Behavior

The command line does not switch port automatically
Environment variable PORT is not supported but it should IMO as I consider that it's default setting in most Node projects.

[richardzcode]

@ThomasG77 it is because you are adding parameter to npm not its script docusaurus-start

To let npm pass arguments to script, you'll need to add a -- in between.

Like this: npm run start -- --port 3001

[ThomasG77]

Thanks @richardzcode for the answer but it's not the issue: I already mentioned your solution in the issue description.

I do not care about option --port 3001. I just want the usual environment variable with PORT=3001.
It don't want it to be a replacement just an alternative as on every project I use and see in the Node landscape, changing port is about PORT=3001 node myservercode.js

[neilsutcliffe]

Is this generally what people expect to happen. Does create-react-app fall-up to 3001 when 3000 is used?

[ThomasG77]

@neilsutcliffe FYI, it uses PORT env variable https://github.com/facebookincubator/create-react-app/blob/master/CONTRIBUTING.md#heuristics
In https://github.com/facebookincubator/create-react-app/blob/master/CONTRIBUTING.md#interactivity, a mention talks about asking to switch port if already busy

[JoelMarcey]

@ThomasG77 Hi. I think this is more a feature request than a bug since you can accomplish the same thing with the command line option. But I see your point in allowing an environment variable as well.

[yangshun]

Closed in #516 , thanks @InternetExplorer7 for the feature!