Node.js is a JavaScript runtime environment that allows you to create server-side applications. While generally known for building web servers, you can also use Node.js to create command line applications, and it can be a powerful tool for shell scripting.
Here’s how you can use Node.js for shell scripting:
1. Creating a Node.js shell script:
A Node.js script is just like any other script. You can create a script file using the “.js” extension, write your Node.js code in the file, and then run the file with the “node” command.
Example:
Filename: helloWorld.js
```
console.log(“Hello World!”);
```
You can run this script using the node command:
```
$ node helloWorld.js
```
This will print “Hello World!” to your console.
1. Using Shebang for Node.js scripts:
To simplify the running of Node.js scripts, you can include a shebang at the top of your script.
Example:
Filename: helloWorld.js
```
#!/usr/bin/env node
console.log(“Hello World!”);
```
To run a Node.js shell script with a shebang, you will need to set the file’s permissions to be executable:
```
$ chmod +x helloWorld.js
```
And then you can directly execute the file:
```
$ ./helloWorld.js
```
1. Using Node.js Modules:
Node.js allows you to use built-in modules and npm packages in your scripts. For example, to interact with the file system, you can use the fs module.
Example:
Filename: readFile.js
```
#!/usr/bin/env node
const fs = require(‘fs’);
const data = fs.readFileSync(‘/etc/passwd’, ‘utf-8’);
console.log(data);
```
This script will print the contents of the “/etc/passwd” file.
1. Reading Command Line Arguments:
You can access the command line arguments passed to your script by using the process.argv array.
Example:
Filename: echoArgs.js
```
#!/usr/bin/env node
console.log(process.argv);
```
And then pass arguments when running the script:
```
$ ./echoArgs.js arg1 arg2
```
This script will print an array of the command line arguments used to call the script.
1. Creating Interactive Command Line Tools:
You can use libraries such as Commander.js or Inquirer.js to create interactive command line tools. These libraries allow you to parse command line arguments, prompt for input in a variety of ways, and format output.
1. Error Handling:
Remember to handle errors properly in your scripts. You can use try-catch blocks, check for error codes, and listen for the ‘error’ event on certain objects such as streams.
Remember to be mindful of asynchronous operations when scripting with Node.js. Many operations in Node.js are asynchronous, so you’ll need to handle them correctly to ensure your script behaves as expected.
