Pass command line args to npm scripts in package.json

Question

I have the below scripts in my package.json:

"scripts": {     "vumper": "node node_modules/vumper/index.js",     "format": "prettier --single-quote -width=80 --write package.json"  }, 

The 'vumper' package takes in a command line argument (such as 'dv'). What I would like to be able to do is have a command that runs both of these in succession.

Essentially, I would like to be able to run:

npm run vumber dv 

and then

npm run format 

but in one command, something like

npm run my-build dv 

which would run both of the above commands, correctly accepting the command line argument 'dv' and passing it to the first npm run vumper. Is this possible?

Answer 1

Short Answer:

Essentially, what you're wanting is to have an npm-script something like this, whereby <arg-here> is provide via the CLI;

... "scripts": {   "my-build": "npm run vumper <arg-here> && npm run format",   ... }, ... 

However, unfortunately npm does not have a built-in feature to achieve this.

The special npm option --, (refer to the end of Solution 1 below for further info about this option), can only be used to pass an argument to the END of a script but NOT into the MIDDLE. So, if your two commands were in the opposite order, the -- option could be used like this:

... "scripts": {   "my-build": "npm run format && npm run vumper --",   ... }, ... 

To overcome the limitation of there being no built-in feature to pass an argument into the MIDDLE of a script consider the following solutions:

1. For a Bash only solution refer to the "Solution 1" section.

2. If cross platform support is required then follow the solution described in the "Solution 2" section.

---

Solution 1 - Bash (MacOS/Linux/ etc..):

Configure your my-build script in the scripts section of package.json to invoke a Bash shell function, as shown below:

package.json

... "scripts": {   "my-build": "func() { npm run vumper \"$1\" && npm run format; }; func",   "vumper": "node node_modules/vumper/index.js",   "format": "prettier --single-quote -width=80 --write package.json" }, ... 

Explanation:

The Bash function named func does the following:

1. Firstly runs npm run vumper <arg>. Whereby <arg> will be the shell argument passed via the CLI. It is referenced in the script using $1 (i.e. the first positional parameter/argument).
2. Subsequently it runs the script named format via the command npm run format.

These two npm run commands are chained using the && operator, so the second npm run format command will only run if the initial npm run vumper <arg> command completes successfully (i.e. returns a 0 exit code).

Running my-build script:

To invoke my-build via your CLI you'll need to run:

npm run my-build -- dv 

Note:

1. In this instance the trailing dv part is the argument that will be passed to your vumper script.

2. The special option -- must be specified before the argument. The docs describe the -- option as:

   ... The special option -- is used by getopt to delimit the end of the options. npm will pass all the arguments after the -- directly to your script: ... The arguments will only be passed to the script specified after npm run and not to any pre or post script.

---

Solution 2 - Cross-platform:

For a cross-platform solution, (one which works successfully with Bash, Windows Command Prompt / cmd.exe, and PowerShell etc..), you'll need to utilize a nodejs helper script as follows.

run.js

Let's name the nodejs script run.js and save it in the projects root directory, at the same level as package.json.

const execSync = require('child_process').execSync;  const arg = process.argv[2] || 'dv'; // Default value `dv` if no args provided via CLI.  execSync('npm run vumper ' + arg, {stdio:[0, 1, 2]}); execSync('npm run format', {stdio:[0, 1, 2]}); 

package.json

Configure your my-build script to invoke run.js as follows:

... "scripts": {   "my-build": "node run",   "vumper": "node node_modules/vumper/index.js",   "format": "prettier --single-quote -width=80 --write package.json" }, ... 

Running my-build script:

As per Solution 1, to invoke my-build via your CLI you'll need to run:

npm run my-build -- dv 

Explanation:

• run.js utilizes process.argv to obtain the argument passed via the CLI (e.g. dv). If no argument is provided when running npm run my-build the default value, (i.e. dv), is passed to the vumper npm-script.

• run.js also utilizes child_process.execSync(...) to shell-out/invoke the two npm run commands.

Answer 2

Npm now has a built-in option to pass cli arguments directly to scripts. The cli arguments are stored in environmenet variables with prefix npm_config_<flagname>, and they required a very strict syntax, with the form --<flagname>=<flagvalue>.

Example:

 "my-build": "npm run vumper %npm_config_myflag% && npm run format", 

In the terminal, run npm run my-build --myflag=my_value to execute npm run vumper my_value && npm run format.

Note:

To refer the environment variable in the npm script, you have to use the platform specific syntax, ie %npm_config_myflag% in Windows or $npm_config_myflag in Linux.

UPDATE:

To avoid risks of conflict with the npm_config variables used to configure npm itself, just prefix your arguments with a unique prefix, such as the name of your app.

The potential conflict is a very common problem, which applies in many contexts: any application could use environment variables already used by other applications; for this reason, the environment variables are usually prefixed with the name of the application (eg NVM_HOME, JAVA_HOME). But this potential conflict is not a good reason to avoid using environment variables. The same in my opinion applies to npm params / npm_config env vars. The doc does not say anything about the risk of conflicts, implying I guess they should be managed as usual.