(Command Line Output)

clout is a package that helps you print user-friendly output messages from your Go command line applications.


import (

Why clout?

Clout helps you print readable and consistent messages using a familiar klog-like API. It's unobtrusive, and designed to enable you to write command line tools without having to worry about the specifics of ANSI colors or stdout/stderr best practices.

Messages Types

Instead of asking you to figure out which output stream a message should be destined for, clout provides with you different types of messages that you can print:

Constant Usage
Status An update to the program's current status.
Info An informational message.
Warning A warning about a potential issue.
Deprecation A warning about a feature which will be removed or unsupported in the future.
Error A severe error.

By default, clout will direct these messages into an appropriate output stream. Warning and error messages will go to the standard error, and all other messages will go to the standard output.

Configurable Verbosity

Just like klog, clout supports different verbosity levels. If you want to provide extra debug information without littering the code with if-statements, you can do that:

clout.V(2).Infof("Processing %s", file)            // Visible by default.
clout.V(4).Statusf("%s: Unmarshalling yaml", file) // Only visible with verbosity 4 or higher.

Best Practices

The following table shows the best practices for using verbosity levels. It's based on the Kubernetes logging best practices:

Level For
V(0) Programmer errors, logging extra info about a panic, cli argument handling.
V(1) Information about config, errors.
V(2) System state, log messages.
V(3) Extended info about system state changes.
V(4) Logging in "thorny parts of code".
V(5) Trace level verbosity.

Color Support

When your terminal supports colors, giant walls of plain text can be unwieldy. clout helps you with that by providing color support (Linux/MacOS only) with no extra burden on you:

  • Warning messages will be prefixed with "warning: " and automatically colored yellow.
  • Deprecation messages will be prefixed with "deprecated: " and automatically colored yellow.
  • Error messages will be prefixed with "error: " and automatically colored red.

And if you have any text that you feel should be highlighted to stand out (e.g. paths)? You can simply wrap parameters in a Highlight, and clout will handle it.

Conditional Colors

Best of all, colors are enabled conditionally. If someone pipes your command's output, colors will be disabled automatically. clout even supports the NO_COLOR standard ;)


import (

func main() {
    clout.V(2).Infof("Initializing application...")
    // -> Initializing application...
    clout.V(3).Info("Args: %#v", os.Args)
    // This won't print anything, because the default verbosity is level 2.
    if len(os.Args) != 2 {
        clout.V(1).Error("not enough arguments")
        // -> error: not enough arguments
    clout.V(2).Infof("Hello, %s.", highlight.Cyan(os.Args[1]))
    // On supported systems, SOME_EXECUTABLE_NAME will be cyan.

For more detailed examples, feel free to check out the example directory.


MIT License