# Getting CLI Arguments in NodeJS

Sometimes we want to pass parameters to our NodeJS application. This can be a situation, especially when we run our codes on the servers or in a local development environment. I know we have a `.env` file and we should use it almost every time with appropriate helper packages (etc _dotenv_ ). But isn't it good if we could pass our arguments to our application when we are starting it?  
Luckily yes we can!  
Let's make a simple application that has a only duty to write **prime numbers between two numbers**, and we will pass our **two numbers** from CLI.

1. First, create a `primeNumberPrinter.js` file.
2. Now let's add our _helper function_ and _main function_:

   ```js
   /*
    * if a number divided by any number
    * smaller than or equal to its square root is not a prime number
    */
   const checkPrime = (num) => {
     if (num <= 1) return false; // Less than 2 is not prime
     for (let i = 2; i <= num ** 0.5; i++) {
       // num ** 0.5: square root of num, can be used also Math.sqrt()
       if (num % i == 0) {
         return false;
       }
     }
     return true;
   };

   const printPrimeNumsBetween = (initNum, endNum) => {
     for (let i = initNum; i <= endNum; i++) {
       if (checkPrime(i)) {
         console.log(i);
       }
     }
   };
   ```

3. Now let's figure out how to get our arguments from CLI. When we pass arguments to our application, like

   ```bash
   node primeNumberPrinter.js <FirstNum> <SecondNum>
   ```

   NodeJS will create an `argv` array in the main `process` object. We can reach this array in our code like:

   ```js
   // primeNumberPrinter.js
   ...
   const mainArgumentsArray = process.argv;
   console.log(mainArgumentsArray);
   ```

   If you console this array by just running our file from CLI,

   ```bash
    node primeNumberPrinter
   ```

   you see there are already **2 elements, the first one is the NodeJS bin file path, second is our file's(primeNumberPrinter.js) path**.

   ```bash
    [
    'C:\\Program Files\\nodejs\\node.exe',
    'C:\\Users\\admin\\Desktop\\info\\primeNumberPrinter.js'
    ]
   ```

   Our arguments will be added to this array by order as `string`, and to get our `arguments`, we should `slice` from `mainArgumentsArray`.

   ```js
   // primeNumberPrinter.js
   ...
   const arguments = mainArgumentsArray.slice(2); // process.argv.slice(2)
   ```

4. Add now we have to this line to print to console our prime numbers. Now our code looks like this:

   ```js
   // primeNumberPrinter.js
   const checkPrime = (num) => {
     if (num <= 1) return false;
     for (let i = 2; i <= num ** 0.5; i++) {
       if (num % i == 0) {
         return false;
       }
     }
     return true;
   };

   const printPrimeNumsBetween = (initNum, endNum) => {
     for (let i = initNum; i <= endNum; i++) {
       if (checkPrime(i)) {
         console.log(i);
       }
     }
   };
   const mainArgumentsArray = process.argv;
   const arguments = mainArgumentsArray.slice(2);
   printPrimeNumsBetween(+arguments[0], +arguments[1]);  // + makes number
   ```

5. Now when we enter from CLI,
   ```bash
   node primeNumberPrinter 3 9
   3
   5
   9
   ```
   we can get our result.

Instead of downloading a whole package, we can use this feature for passing some test data, keys, and secrets.    
  
Hope this helps you.  
   
Thank you for reading.