How Can I Pass Dynamic Command Line Arguments to npm Scripts?

Achieving Dynamic Command Line Arguments with npm Scripts

In the realms of development, it's often desirable to pass arguments to scripts executed through npm commands. This article delves into the possibilities of achieving this with npm scripts. Our focus will be on newer versions of npm (2 and above) and their robust support for passing arguments to scripts.

npm 2 and Newer

With npm 2 and subsequent versions, the syntax for passing arguments to npm run commands is as follows:

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

The separator '--' is crucial, as it divides parameters destined for npm from those intended for your script. Here's an illustration:

npm run grunt -- task:target  // Invokes `grunt task:target`
npm run server -- --port=1337 // Invokes `node server.js --port=1337`

Note that if your argument doesn't start with '-' or '--', the explicit '--' separator is optional but still recommended for clarity.

npm run grunt task:target     // Also invokes `grunt task:target`

But be cautious of arguments beginning with '-' or '--', as npm will interpret them as its own options rather than passing them to the script.

['C:\Program Files\nodejs\node.exe', 'C:\git\myrepo\test.js', 'foobar']  // Argument passed to script

['C:\Program Files\nodejs\node.exe', 'C:\git\myrepo\test.js']  // Argument not passed to script

To retrieve the parameter value within your script, process.argv can be utilized. For more complex handling, libraries like yargs or minimist are ideal for parsing named parameters and handling whitespace-separated command line arguments exposed by process.argv.

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