A simple cross platform library for writing colored text to a terminal. This library writes colored text either using standard ANSI escape sequences or by interacting with the Windows console. Several convenient abstractions are provided for use in single-threaded or multi-threaded command line applications.

Dual-licensed under MIT or the UNLICENSE.

https://docs.rs/termcolor

Run cargo add termcolor to add this dependency to your Cargo.toml file.

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 stdout or stderr 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.

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

fn write_green() -> io::Result<()> {
    let mut stdout = StandardStream::stdout(ColorChoice::Always);
    stdout.set_color(ColorSpec::new().set_fg(Some(Color::Green)))?;
    writeln!(&mut stdout, "green text!")
}

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 termcolor::WriteColor.

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

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

fn write_green() -> io::Result<()> {
    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)
}

When building a writer with termcolor, the caller must provide a ColorChoice selection. When the color choice is Auto, termcolor will attempt to determine whether colors should be enabled by inspecting the environment. Currently, termcolor will inspect the TERM and NO_COLOR environment variables:

• If NO_COLOR is set to any value, then colors will be suppressed.
• If TERM is set to dumb, then colors will be suppressed.
• In non-Windows environments, if TERM is not set, then colors will be suppressed.

This decision procedure may change over time.

Currently, termcolor does not attempt to detect whether a tty is present or not. To achieve that, please use std::io::IsTerminal.

This crate's minimum supported rustc version is 1.34.0.

The current policy is that the minimum Rust version required to use this crate can be increased in minor version updates. For example, if crate 1.0 requires Rust 1.20.0, then crate 1.0.z for all values of z will also require Rust 1.20.0 or newer. However, crate 1.y for y > 0 may require a newer minimum version of Rust.

In general, this crate will be conservative with respect to the minimum supported version of Rust.