Dart Process

last modified April 4, 2025

The Process class in Dart provides functionality to run and interact with system processes. It’s part of Dart’s dart:io library and works in command-line applications.

Process allows executing commands, reading their output, writing to their input, and monitoring their exit status. It’s essential for system-level programming in Dart.

Basic Definition

Process represents a native system process. It provides methods to start, communicate with, and control external programs.

Key features include process lifecycle management, I/O stream access, and exit code handling. It supports both synchronous and asynchronous operations.

Running a Simple Command

This example shows how to run a basic system command and read its output.

main.dart

import ‘dart:io’;

void main() async { var process = await Process.start(’ls’, [’-l’]);

process.stdout.transform(utf8.decoder).listen((data) { print(data); });

var exitCode = await process.exitCode; print(‘Exit code: $exitCode’); }

We start the ’ls -l’ command asynchronously and listen to its stdout stream. The exitCode future completes when the process terminates.

$ dart main.dart total 12 -rw-r–r– 1 user user 220 Apr 4 10:00 main.dart Exit code: 0

Handling Input and Output

This example demonstrates two-way communication with a process.

main.dart

import ‘dart:io’; import ‘dart:convert’;

void main() async { var process = await Process.start(‘grep’, [‘dart’]);

process.stdin.writeln(‘This line contains dart’); process.stdin.writeln(‘This line does not’); await process.stdin.close();

process.stdout.transform(utf8.decoder).listen((data) { print(‘Found: $data’); });

await process.exitCode; }

We start grep to filter lines containing ‘dart’. We write to its stdin and read filtered results from stdout. Always close stdin when done writing.

$ dart main.dart Found: This line contains dart

Running Synchronously

This example shows how to run a command and wait for completion.

main.dart

import ‘dart:io’;

void main() async { var result = await Process.run(‘date’, [’+%Y-%m-%d’]);

print(‘Output: ${result.stdout}’); print(‘Error: ${result.stderr}’); print(‘Exit code: ${result.exitCode}’); }

Process.run executes the command and collects all output. It returns a ProcessResult with stdout, stderr, and exit code when complete.

$ dart main.dart Output: 2025-04-04

Error: Exit code: 0

Handling Errors

This example demonstrates error handling when a process fails.

main.dart

import ‘dart:io’;

void main() async { try { var result = await Process.run(’nonexistent’, []); print(result.stdout); } on ProcessException catch (e) { print(‘Process failed: ${e.message}’); } }

We attempt to run a non-existent command. ProcessException is thrown when the process cannot be started. Always handle potential process failures.

$ dart main.dart Process failed: No such file or directory

Running Multiple Processes

This example shows how to run and manage multiple processes concurrently.

main.dart

import ‘dart:io’;

void main() async { var processes = [ Process.start(‘sleep’, [‘2’]), Process.start(’echo’, [‘hello’]), Process.start(‘date’, []), ];

var results = await Future.wait(processes);

for (var process in results) { print(‘Process ${process.pid} exited with ${await process.exitCode}’); } }

We start three processes simultaneously and wait for all to complete. Each Process object provides the process ID and exit status.

$ dart main.dart Process 1234 exited with 0 Process 1235 exited with 0 Process 1236 exited with 0

Best Practices

• Stream handling: Always listen to stdout/stderr to prevent deadlocks

• Error handling: Catch ProcessException for startup failures

• Resource cleanup: Close stdin and cancel stream subscriptions

• Timeouts: Consider using timeouts for long-running processes

• Security: Sanitize command arguments to prevent injection

Source

Dart Process Documentation

This tutorial covered Dart’s Process class with practical examples showing command execution, I/O handling, error management, and concurrent processes.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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