supportscolor

supports-color

Go library to detect whether a terminal supports color, and enables ANSI color support in recent Windows 10 builds.

This is a port of the Node.js package supports-color v8.1.1 by Sindre Sorhus and Josh Junon.

Install

$ go get github.com/jwalton/go-supportscolor

Usage

import (
    "fmt"
    "github.com/jwalton/go-supportscolor"
)

if supportscolor.Stdout().SupportsColor {
    fmt.Println("Terminal stdout supports color")
}

if supportscolor.Stdout().Has256 {
    fmt.Println("Terminal stdout supports 256 colors")
}

if supportscolor.Stderr().Has16m {
    fmt.Println("Terminal stderr supports 16 million colors (true color)")
}

Windows 10 Support

supportscolor is cross-platform, and will work on Linux and MacOS systems, but will also work on Windows 10.

Many ANSI color libraries for Go do a poor job of handling colors in Windows. This is because historically, Windows has not supported ANSI color codes, so hacks like ansicon or go-colorable were required. However, Windows 10 has supported ANSI escape codes since 2017 (build 10586 for 256 color support, and build 14931 for 16.7 million true color support). In Windows Terminal this is enabled by default, but in CMD.EXE or PowerShell, ANSI support must be enabled via ENABLE_VIRTUAL_TERMINAL_PROCESSING.

This library takes care of all of this for you, though - if you call supportscolor.Stdout() on a modern build of Windows 10, it will set the ENABLE_VIRTUAL_TERMINAL_PROCESSING console mode automatically if required, and return the correct color level, and then you can just write ANSI escape codes to stdout and not worry about it. If someone uses your app on an old version of Windows, this will return SupportsColor == false, and you can write black and white to stdout.

API

Returns a supportscolor.Support with a Stdout() and Stderr() function for testing either stream. (There's one for stdout and one for stderr, because if you run mycmd > foo.txt then stdout would be redirected to a file, and since it would not be a TTY would not have color support, while stderr would still be going to the console and would have color support.)

The Stdout()/Stderr() objects specify a level of support for color through a .Level property and a corresponding flag:

• .Level = None and .SupportsColor = false: No color support
• .Level = Basic and .SupportsColor = true: Basic color support (16 colors)
• .Level = Ansi256 and .Has256 = true: 256 color support
• .Level = Ansi16m and .Has16m = true: True color support (16 million colors)

supportscolor.SupportsColor(fd, ...options)

Additionally, supportscolor exposes the .SupportsColor() function that takes an arbitrary file descriptor (e.g. os.Stdout.Fd()) and options and will (re-)evaluate color support for an arbitrary stream.

For example, supportscolor.Stdout() is the equivalent of supportscolor.SupportsColor(os.Stdout.Fd()).

Available options are:

• supportscolor.IsTTYOption(isTTY bool) - Force whether the given file should be considered a TTY or not. If this not specified, TTY status will be detected automatically via term.IsTerminal().
• supportscolor.SniffFlagsOption(sniffFlags bool) - By default it is true, which instructs SupportsColor() to sniff os.Args for the multitude of --color flags (see Info below). If false, then os.Args is not considered when determining color support.

Info

By default, supportscolor checks os.Args for the --color and --no-color CLI flags.

For situations where using --color is not possible, use the environment variable FORCE_COLOR=1 (level 1 - 16 colors), FORCE_COLOR=2 (level 2 - 256 colors), or FORCE_COLOR=3 (level 3 - true color) to forcefully enable color, or FORCE_COLOR=0 to forcefully disable. The use of FORCE_COLOR overrides all other color support checks.

If NO_COLOR is specified and FORCE_COLOR is not, then colors will be disabled.

Explicit 256/True color mode can be enabled using the --color=256 and --color=16m flags, respectively.