Sending command line arguments to npm script

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?

Solutions/Answers:

Solution 1:

Edit 2014.10.30: It’s possible to pass args to npm run as of npm 2.0.0

The syntax is as follows:

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

Note the necessary --. It is needed to separate the params passed to npm command itself and params passed to your script.

So if you have in package.json

"scripts": {
    "grunt": "grunt",
    "server": "node server.js"
}

Then the following commands would be equivalent:

grunt task:target => npm run grunt -- task:target

node server.js --port=1337 => npm run server -- --port=1337

To get the parameter value, see this question. For reading named parameters, it’s probably best to use a parsing library like yargs or minimist; nodejs exposes process.argv globally, containing command line parameter values, but this is a low-level API (whitespace-separated array of strings, as provided by the operating system to the node executable).

Edit 2013.10.03: It’s not currently possible directly. But there’s a related GitHub issue opened on npm to implement the behavior you’re asking for. Seems the consensus is to have this implemented, but it depends on another issue being solved before.

Original answer: As a some kind of workaround (though not very handy), you can do as follows:

Say your package name from package.json is myPackage and you have also

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

Then add in package.json:

"config": {
    "myPort": "8080"
}

And in your script.js:

// defaulting to 8080 in case if script invoked not via "npm run-script" but directly
var port = process.env.npm_package_config_myPort || 8080

That way, by default npm start will use 8080. You can however configure it (the value will be stored by npm in its internal storage):

npm config set myPackage:myPort 9090

Then, when invoking npm start, 9090 will be used (the default from package.json gets overridden).

Solution 2:

You asked to be able to run something like npm start 8080. This is possible without needing to modify script.js or configuration files as follows.

For example, in your "scripts" JSON value, include–

"start": "node ./script.js server $PORT"

And then from the command-line:

$ PORT=8080 npm start

I have confirmed that this works using bash and npm 1.4.23. Note that this work-around does not require GitHub npm issue #3494 to be resolved.

Solution 3:

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

Solution 4:

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");
}

Solution 5:

npm 2.x support cli args

Command

npm run-script start -- --foo=3

Package.json

"start": "node ./index.js"

Index.js

console.log('process.argv', process.argv);

Solution 6:

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

As an example try it with a simple script which just logs the provided arguments to standard out 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