# Crate termcolor

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This crate provides a cross platform abstraction for writing colored text to a terminal. Colors are written using either ANSI escape sequences or by communicating with a Windows console. Much of this API was motivated by use inside command line applications, where colors or styles can be configured by the end user and/or the environment.

This crate also provides platform independent support for writing colored text to an in memory buffer. While this is easy to do with ANSI escape sequences (because they are in the buffer themselves), it is trickier to do with the Windows console API, which requires synchronous communication.

## Organization

The `WriteColor` trait extends the `io::Write` trait with methods for setting colors or resetting them.

`StandardStream` and `StandardStreamLock` both satisfy `WriteColor` and are analogous to `std::io::Stdout` and `std::io::StdoutLock`, or `std::io::Stderr` and `std::io::StderrLock`.

`Buffer` is an in memory buffer that supports colored text. In a parallel program, each thread might write to its own buffer. A buffer can be printed to using a `BufferWriter`. The advantage of this design is that each thread can work in parallel on a buffer without having to synchronize access to global resources such as the Windows console. Moreover, this design also prevents interleaving of buffer output.

`Ansi` and `NoColor` both satisfy `WriteColor` for arbitrary implementors of `io::Write`. These types are useful when you know exactly what you need. An analogous type for the Windows console is not provided since it cannot exist.

## Example: using `StandardStream`

The `StandardStream` type in this crate works similarly to `std::io::Stdout`, except it is augmented with methods for coloring by the `WriteColor` trait. For example, to write some green text:

    use std::io::Write;
    use termcolor::{Color, ColorChoice, ColorSpec, StandardStream, WriteColor};

    let mut stdout = StandardStream::stdout(ColorChoice::Always);
    stdout.set_color(ColorSpec::new().set_fg(Some(Color::Green)))?;
    writeln!(&mut stdout, "green text!")?;

Note that any text written to the terminal now will be colored green when using ANSI escape sequences, even if it is written via stderr, and even if stderr had previously been set to `Color::Red`. Users will need to manage any color changes themselves by calling `WriteColor::set_color`, and this may include calling `WriteColor::reset` before the program exits to a shell.

## Example: using `BufferWriter`

A `BufferWriter` can create buffers and write buffers to stdout or stderr. It does not implement `io::Write` or `WriteColor` itself. Instead, `Buffer` implements `io::Write` and `io::WriteColor`.

This example shows how to print some green text to stderr.

    use std::io::Write;
    use termcolor::{BufferWriter, Color, ColorChoice, ColorSpec, WriteColor};

    let mut bufwtr = BufferWriter::stderr(ColorChoice::Always);
    let mut buffer = bufwtr.buffer();
    buffer.set_color(ColorSpec::new().set_fg(Some(Color::Green)))?;
    writeln!(&mut buffer, "green text!")?;
    bufwtr.print(&buffer)?;

## Detecting presence of a terminal

In many scenarios when using color, one often wants to enable colors automatically when writing to a terminal and disable colors automatically when writing to anything else. The typical way to achieve this in Unix environments is via libc’s `isatty` function. Unfortunately, this notoriously does not work well in Windows environments. To work around that, the currently recommended solution is to use the `atty` crate, which goes out of its way to get this as right as possible in Windows environments.

For example, in a command line application that exposes a `--color` flag, your logic for how to enable colors might look like this:

ⓘ

    use atty;
    use termcolor::{ColorChoice, StandardStream};

    let preference = argv.get_flag("color").unwrap_or("auto");
    let choice = match preference {
        "always" => ColorChoice::Always,
        "ansi" => ColorChoice::AlwaysAnsi,
        "auto" => {
            if atty::is(atty::Stream::Stdout) {
                ColorChoice::Auto
            } else {
                ColorChoice::Never
            }
        }
        _ => ColorChoice::Never,
    };
    let stdout = StandardStream::stdout(choice);
    // ... write to stdout

Currently, `termcolor` does not provide anything to do this for you.

## Structs

Ansi

Satisfies `WriteColor` using standard ANSI escape sequences.

Buffer

Write colored text to memory.

BufferWriter

Writes colored buffers to stdout or stderr.

BufferedStandardStream

Like `StandardStream`, but does buffered writing.

ColorSpec

A color specification.

NoColor

Satisfies `WriteColor` but ignores all color options.

ParseColorError

An error from parsing an invalid color specification.

StandardStream

Satisfies `io::Write` and `WriteColor`, and supports optional coloring to either of the standard output streams, stdout and stderr.

StandardStreamLock

`StandardStreamLock` is a locked reference to a `StandardStream`.

## Enums

Color

The set of available colors for the terminal foreground/background.

ColorChoice

ColorChoice represents the color preferences of an end user.

## Traits

WriteColor

This trait describes the behavior of writers that support colored output.