How to handle user Input and Output in Dart CLI

Sakshi Rai

17 January 2025

In this blog, we will learn about how to handle user Input and Output in Dart CLI.

Introduction:

Dart is a versatile programming language known for its role in building cross-platform mobile apps with Flutter.

However, its capabilities extend far beyond mobile development, making it an excellent choice for building lightweight, efficient Command-Line Interface applications.

Whether you’re building a simple utility tool or a more complex application, handling user input and output is fundamental.

Implementation:

Getting Started with a Dart CLI Application:-

First, verify that Dart is installed on your machine. If it isn’t, download it from dart.dev. After you’ve installed it, you can create a new CLI project:

dart create -t console cli_application
cd cli_application

1 2	dart create -t console cli_application cd cli_application

Reading User Input:-

Dart provides the stdin object from the dart:io library to read user input. Here’s an example:

import 'dart:io';

void main() {
  print('Enter your name:');
  String? name = stdin.readLineSync(); // Read user input
  if (name != null && name.isNotEmpty) {
    print('Hello, $name!');
  } else {
    print('Name cannot be empty.');
  }
}

import 'dart:io';

void main() {

print('Enter your name:');

String? name = stdin.readLineSync(); // Read user input

if (name != null && name.isNotEmpty) {

print('Hello, $name!');

} else {

print('Name cannot be empty.');

}

Key Points:

stdin.readLineSync() reads input as a string.
Always check for null values since the user might just press Enter.

Writing Output to the Console:-

You can use the print() function to display output in the console. For example:

void main() {
  print('Welcome to the Dart CLI Application!');
  print('This application demonstrates input and output handling.');
}

void main() {

print('Welcome to the Dart CLI Application!');

print('This application demonstrates input and output handling.');

}

For formatted output, use string interpolation or concatenation:

void main() {
  String name = 'Dart Developer';
  int age = 10;
  print('Name: $name, Age: $age');
}

void main() {

String name = 'Dart Developer';

int age = 10;

print('Name: $name, Age: $age');

}

Handling Errors in User Input:-

Input validation is crucial for a robust CLI application. Here’s how to validate numeric input:

import 'dart:io';

void main() {
  print('Enter your age:');
  String? input = stdin.readLineSync();
  if (input != null) {
    try {
      int age = int.parse(input); // Convert string to int
      print('You are $age years old.');
    } catch (e) {
      print('Invalid input. Please enter a valid number.');
    }
  } else {
    print('No input provided.');
  }
}

import 'dart:io';

void main() {

print('Enter your age:');

String? input = stdin.readLineSync();

if (input != null) {

try {

int age = int.parse(input); // Convert string to int

print('You are $age years old.');

} catch (e) {

print('Invalid input. Please enter a valid number.');

}

} else {

print('No input provided.');

}

Using Command-Line Arguments:-

Dart CLI apps can also accept arguments directly when the app is executed. Here’s an example:

void main(List<String> arguments) {
  if (arguments.isEmpty) {
    print('No arguments provided. Usage: dart app.dart <your-name>');
  } else {
    print('Hello, ${arguments[0]}!');
  }
}

void main(List<String> arguments) {

if (arguments.isEmpty) {

print('No arguments provided. Usage: dart app.dart <your-name>');

} else {

print('Hello, ${arguments[0]}!');

}

Run this script with:

dart run bin/cli_application.dart Sakshi

1	dart run bin/cli_application.dart Sakshi

Conclusion:

Handling user input and output effectively is the cornerstone of creating interactive and user-friendly CLI applications.

You can explore other blogs from this site.

Thanks for reading this blog ❤️

Hope this blog helped you to better understand how to handle user Input and Output in Dart CLI.

You can check the official documentation here