In today's quick tip, we will learn how easy it is to read and write files in Dart. We will use the File object of the 'dart:io' library to achieve this.
To follow along, generate the console-full project with stagehand:
$ mkdir my_app && cd my_app
$ stagehand console-full
See the solution in action below:
Here's the full solution:
import 'dart:io';
main() async {
var file = File('data.txt');
var contents;
if (await file.exists()) {
// Read file
contents = await file.readAsString();
print(contents);
// Write file
var fileCopy = await File('data-copy.txt').writeAsString(contents);
print(await fileCopy.exists());
print(await fileCopy.length());
}
}
Extending the example
1. How to better specify the file path
Install the path package by adding the dependency to your pubspec.yaml file:
dependencies:
path: ^1.6.2
And running pub get in your terminal.
Import this at the top of bin/main.dart and amend the path as follows:
import 'dart:io';
import 'package:path/path.dart';
void main() async {
var pathToFile = join(dirname(Platform.script.toFilePath()), '..', 'data.txt');
var file = File(pathToFile);
..
..
}
2. How to read the file line by line
We can create a stream to read the file:
import 'dart:convert'; // Contains the `Utf8Decoder` and `LineSplitter` stream transformers
..
..
if (await file.exists()) {
// Read file
contents = StringBuffer();
var contentStream = file.openRead();
contentStream
.transform(Utf8Decoder())
.transform(LineSplitter())
.listen((String line) => contents.write(line), // Add line to our StringBuffer object
onDone: () => print(contents.toString()), // Call toString() method to receive the complete data
onError: (e) => print('[Problems]: $e'));
..
..
}
..
..
A good use case for this would be processing a file containing environment variables, like the file contents below:
PORT=8080
API_KEY=lkjsk453lkslfkl5
API_USER=jermaineo
Please leave your feedback in the comments, and let me know what you would like to see demonstrated next!
Subscribe to the Youtube channel for upcoming videos on Dart. Thanks!
Like, share and follow me 😍 for more content on Dart.
Further reading:
Top comments (3)
Thanks for your article!
If I were lazy to look up the documentation myself, I'd like to extend this example by two things:
Thanks @sandordargo for your feedback. I've updated the article on those points.
You're awesome, man!