Sending command line arguments to npm script

Question

The scripts portion of my package.json currently looks like this:

"scripts": {
    "start": "node ./script.js server"
}

...which means I can run npm start to start the server. So far so good.

However, I would like to be able to run something like npm start 8080 and have the argument(s) passed to script.js (e.g. npm start 8080 => node ./script.js server 8080). Is this possible?

Answer 1

jakub.g's answer is correct, however an example using grunt seems a bit complex.

So my simpler answer:

- Sending a command line argument to an npm script

Syntax for sending command line arguments to an npm script:

npm run [command] [-- <args>]

Imagine we have an npm start task in our package.json to kick off webpack dev server:

"scripts": {
  "start": "webpack-dev-server --port 5000"
},

We run this from the command line with npm start

Now if we want to pass in a port to the npm script:

"scripts": {
  "start": "webpack-dev-server --port process.env.port || 8080"
},

running this and passing the port e.g. 5000 via command line would be as follows:

npm start --port:5000

- Using package.json config:

As mentioned by jakub.g, you can alternatively set params in the config of your package.json

"config": {
  "myPort": "5000"
}

"scripts": {
  "start": "webpack-dev-server --port process.env.npm_package_config_myPort || 8080"
},

npm start will use the port specified in your config, or alternatively you can override it

npm config set myPackage:myPort 3000

- Setting a param in your npm script

An example of reading a variable set in your npm script. In this example NODE_ENV

"scripts": {
  "start:prod": "NODE_ENV=prod node server.js",
  "start:dev": "NODE_ENV=dev node server.js"
},

read NODE_ENV in server.js either prod or dev

var env = process.env.NODE_ENV || 'prod'

if(env === 'dev'){
    var app = require("./serverDev.js");
} else {
    var app = require("./serverProd.js");
}

Answer 2

You could also do that:

In package.json:

"scripts": {
    "cool": "./cool.js"
}

In cool.js:

 console.log({ myVar: process.env.npm_config_myVar });

In CLI:

npm --myVar=something run-script cool

Should output:

{ myVar: 'something' }

Update: Using npm 3.10.3, it appears that it lowercases the process.env.npm_config_ variables? I'm also using better-npm-run, so I'm not sure if this is vanilla default behavior or not, but this answer is working. Instead of process.env.npm_config_myVar, try process.env.npm_config_myvar

Answer 3

Use process.argv in your code then just provide a trailing $* to your scripts value entry.

echoargs.js:

console.log('arguments: ' + process.argv.slice(2));

package.json:

"scripts": {
    "start": "node echoargs.js $*"
}

Examples:

> npm start 1 2 3
arguments: 1,2,3

process.argv[0] is the executable (node), process.argv[1] is your script.

Tested with npm v5.3.0 and node v8.4.0

Answer 4

If you want to pass arguments to the middle of an npm script, as opposed to just having them appended to the end, then inline environment variables seem to work nicely:

"scripts": {
  "dev": "BABEL_ARGS=-w npm run build && cd lib/server && nodemon index.js",
  "start": "npm run build && node lib/server/index.js",
  "build": "mkdir -p lib && babel $BABEL_ARGS -s inline --stage 0 src -d lib",
},

Here, npm run dev passes the -w watch flag to babel, but npm run start just runs a regular build once.

Answer 5

I've found this question while I was trying to solve my issue with running sequelize seed:generate cli command:

node_modules/.bin/sequelize seed:generate --name=user

Let me get to the point. I wanted to have a short script command in my package.json file and to provide --name argument at the same time

The answer came after some experiments. Here is my command in package.json

"scripts: {
  "seed:generate":"NODE_ENV=development node_modules/.bin/sequelize seed:generate"
}

... and here is and example of running it in terminal to generate a seed file for a user

> yarn seed:generate --name=user

> npm run seed:generate -- --name=user

FYI

yarn -v
1.6.0

npm -v
5.6.0

Answer 6

This doesn't really answer your question but you could always use environment variables instead:

"scripts": {
    "start": "PORT=3000 node server.js"
}

Then in your server.js file:

var port = process.env.PORT || 3000;