Ansi Modifier

Dart

Introduction

The package provides the class Ansi holding ANSI modifier codes and the String extension methods style and clearStyle for adding, replacing, and removing ANSI modifiers. It provides Ansi codes for changing the current cursor position.

Usage

Include ansi_modifier as a dependency in your pubspec.yaml file.

1. Changing the Font Style and Colour of Console Output

Use the String extension function style to add new modifiers or to replace existing ones. Use the function clearStyle to remove all Ansi modifier from a string.

import 'package:ansi_modifier/src/ansi.dart';

void main(List<String> args) {
  // Create colorized strings.
  print('\nCreate colorized strings:');
  final blue = 'blueberry'.style(Ansi.blue + Ansi.italic);
  final green = 'green apple'.style(Ansi.green);
  final blueGreen = blue +
      ' and ' +
      green.style(
        Ansi.bold,
        method: Replace.none,
      );
  print('$blue, $green, $blueGreen');

  // Modify a previously colorized string.
  print('\nModify previously colorized strings:');

  // Create custom Ansi modifier.
  final customModifier = Ansi.combine({Ansi.yellow, Ansi.bold, Ansi.underline});

  // Replace first modifier:
  final yellowGreen = blueGreen.style(customModifier, method: Replace.first);

  // Replace all modifiers.
  final magenta =
      yellowGreen.style(Ansi.magenta, method: Replace.clearPrevious);

  // Strip all Ansi modifiers.
  print('$yellowGreen, $magenta, ${magenta.clearStyle()}\n');
}

Runnig the program above produces the following output: Console Output

2. Moving the Current Cursor Position

Ansi codes for moving the current cursor position can be constructed using the constructors .cursorUp, .cursorDown, .cursorForward, .cursorBack, .cursorNextLine, .cursorPreviousLine, and .cursorToColumn.

The example below shows how to change the cursor position using Dart's stdout function write in order to display a progress indicator:

import 'dart:io';

import 'package:ansi_modifier/src/ansi.dart';

void main(List<String> args) async {

  // Emit a periodic stream
  final stream = Stream<String>.periodic(
      const Duration(milliseconds: 500),
      (i) =>
          'Progress timer: '.style(Ansi.grey) +
          ((i * 500 / 1000).toString() + ' s').style(Ansi.green));

  // Listen to the stream and output progress indicator
  final subscription = stream.listen((event) {
    // Place cursor to first column to overwrite previous string.
    stdout.write(Ansi.cursorToColumn(1));
    stdout.write(event);
  });

  /// Add delay ...
  await Future.delayed(Duration(seconds: 5), () {
    print('\n');
    print('After 5 seconds.'.style(Ansi.green));
  });

  await subscription.cancel();
}

The program above produces the following console output: Progress Indicator

Tips and Tricks

  • The String extension method style supports different replacement modes that can be adjusted using the optional argument method.

  • Ansi codes can be combined using the addition operator Anis.red + Ansi.bold, or by using the factory constructor Ansi.combine.

  • Ansi output can be globally disabled by setting Ansi.status = AnsiOutput.disabled or by using the option:

    $ dart --define=isMonochrome=true example/bin/color_example.dart

Features and bugs

If some Ansi modifiers are missing please file an enhancement request at the issue tracker.

Libraries

ansi_modifier