Dart ProcessStartMode

last modified April 4, 2025

The ProcessStartMode class in Dart controls how a new process should be started. It's used with the Process.run and Process.start methods.

ProcessStartMode determines how the standard input, output, and error streams are handled. It's part of Dart's dart:io library for system-level operations.

Basic Definition

ProcessStartMode is an enum that defines process execution modes. It specifies how the process streams should be connected to the parent process.

The available modes are: normal, detached, detachedWithStdio, and inheritsStdio. Each serves different use cases for process execution.

Normal Mode

This example shows the default normal mode where pipes are created for all standard streams.

import 'dart:io';
void main() async {
 var process = await Process.start(
 'dart',
 ['--version'],
 mode: ProcessStartMode.normal
 );
 
 var output = await process.stdout.transform(utf8.decoder).join();
 print('Dart version: $output');
}

In normal mode, the process creates pipes for stdin, stdout, and stderr. The parent process can read/write these streams. This is the default mode.

$ dart main.dart
Dart version: Dart SDK version: 2.19.0 (stable)

Detached Mode

This example demonstrates detached mode where the process runs independently without stream connections.

import 'dart:io';
void main() async {
 var process = await Process.start(
 'sleep',
 ['5'],
 mode: ProcessStartMode.detached
 );
 
 print('Process started with PID: ${process.pid}');
 print('Process will run independently for 5 seconds');
}

In detached mode, the process runs independently with no stream connections. The parent process cannot communicate with the child process via streams.

$ dart main.dart
Process started with PID: 12345
Process will run independently for 5 seconds

Detached With Stdio

This example shows detachedWithStdio mode where the process inherits the parent's standard streams but runs independently.

import 'dart:io';
void main() async {
 var process = await Process.start(
 'dart',
 ['--version'],
 mode: ProcessStartMode.detachedWithStdio
 );
 
 print('Process started with PID: ${process.pid}');
 print('Output will go to parent process stdout');
}

In this mode, the process inherits stdio but runs detached. Output appears in the parent's console, but the parent can't programmatically access streams.

$ dart main.dart
Process started with PID: 12346
Output will go to parent process stdout
Dart SDK version: 2.19.0 (stable)

Inherits Stdio

This example demonstrates inheritsStdio mode where the process shares the parent's standard streams.

import 'dart:io';
void main() async {
 var process = await Process.start(
 'echo',
 ['Hello from child process'],
 mode: ProcessStartMode.inheritsStdio
 );
 
 await process.exitCode;
 print('Child process completed');
}

In inheritsStdio mode, the child process shares the parent's stdin, stdout, and stderr. The output appears directly in the console without redirection.

$ dart main.dart
Hello from child process
Child process completed

Combining Modes with Process.run

This example shows using ProcessStartMode with Process.run for simpler process execution while controlling stream behavior.

import 'dart:io';
void main() async {
 var result = await Process.run(
 'ls',
 ['-l'],
 runInShell: true,
 mode: ProcessStartMode.inheritsStdio
 );
 
 print('Exit code: ${result.exitCode}');
}

Process.run simplifies process execution while still allowing mode control. In this case, output goes directly to console due to inheritsStdio mode.

$ dart main.dart
total 8
-rw-r--r-- 1 user group 123 Apr 4 10:00 main.dart
Exit code: 0

Best Practices

• Default: Use normal mode when you need stream communication
• Background: Use detached for long-running background tasks
• Console: Use inheritsStdio for simple command-line tools
• Security: Be careful with inheritsStdio for sensitive input

Source

Dart ProcessStartMode Documentation

This tutorial covered Dart's ProcessStartMode class with practical examples showing different process execution modes and their use cases.

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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