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tco is a commandline tool and also a Ruby module that allows its users to easily colourize the terminal output of their bash scripts as well as Ruby programs.


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 Project Readme

tco - terminal colours made simple

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The purpose of the tco gem is to make colouring in the terminal as convenient and as simple as possible. It provides a library for your Ruby gems and also a standalone command line tool that you can use anywhere else.


If you've ever worked with the extended colour palette in the terminal, you probably know that it's not really easy to find the colour you want. The palette consists of 256 colours that are evenly sampled through the RGB space. As opposed to the ANSI palette, the colours tend to be the same across different terminals. They are assigned linearly to a set of escape sequences that are used to apply the colours. And that is the problem; searching through the palette is very unintuitive.

On the other hand, selecting a RGB colour using your favourite colour picker is a nice, buttery piece of cake with a bit of cream on top. That is everything you need to do; pass the value to tco and it will sort out all the boring bits for you. Using the RGB value, the library will find the perceptually closest option that is displayable in your terminal and decorate the string with the appropriate escape sequences, letting you focus on more interesting things in life instead.

On top of that, it comes with a simple built-in templating engine that you can use to decorate only the parts that you want without having to split your string into 15 parts. Check out the following examples.

### A few examples

The tco terminal utility allows you to do the simple things you might need in your bash scripts:

Using tco to colour text

However, using tco directly from Ruby gives you much more flexibility. The following short piece of code will draw a rainbow inside your terminal:

require "tco"

rainbow = ["#622e90", "#2d3091", "#00aaea", "#02a552", "#fdea22", "#eb443b", "#f37f5a"]
10.times do
  rainbow.each { |colour| print "    ".bg colour }

tco showing a simple rainbow

And if you add a bit of rmagick to the equation, you can even render whole images in your terminal with no more than 10 lines of code.

require "tco"
require "rmagick""tux.png")[0].each_pixel do |pixel, col, row|
  c = [,,].map { |v| 255*(v/65535.0) }
  print "  ".bg c
  puts if col >= 53

Tux drawn with tco

These were just the basic things you can do with tco. There are many more options and features available, many of them are described in the Usage section just bellow.


You can use either the tco binary for your command line applications or the library directly from your Ruby scripts. Both use cases are explained bellow.

The Ruby library

When it comes to colouring, there are two options available. You can either use the default library interface, or use the String extension that also comes with the library. Both of them offer exactly the same functionality (fg, bg, bright, underline). See the example of both, below:

require "tco"

# The standard interface
puts Tco::fg("#ff0000", Tco::bg("#888888", Tco::bright("London")))
puts Tco::underline "Underground"

# The String object extension
puts "London".fg("#ff0000").bg("#888888").bright
puts "Underground".underline

# Using predefined style
puts "London".style "alert"
puts Tco::style "alert", "Underground"

In the last bit of the example above, I'm referring to a preconfigured style definition. You can set them either system-wide in /etc/tco.conf or just for a single user in the ~/.tco.conf file. They both are just simple YAML files. The precise format of these configuration files is explained at the end of this file.

Changing the configuration on the fly

A notable feature in regards of configuration is the fact, that you can easily change it on-the-fly. This can be useful for adding aliases for colours and defining your own styles just for your application, so you don't have to repeat the same settings all over your script. All these settings will be applied on top of the user and system config files.

require "tco"

Tco::configure do |tco_conf|
  tco_conf.names["white"] = "#000"
  tco_conf.styles["pass"] = {
    "fg" => "#000",
    "bg" => "#00ff00",
    "bright" => false,
    "underline" => false,

Apart from that, the library then contains a few more advanced things which aren't that useful for everyone. Please, have a look at lib/tco/tco.rb if you're interested.

The command-line tool

Using the tco command is just as simple as using the Ruby library. It expects input either as a positional argument or alternatively at the standard input.

Apart from the core functionality, the CLI tool adds support for simple templates that let you markup certain parts of your string. All templates are enclosed in double curly brackets {{fg:bg:ub text}}. Check out the following examples:

tco -f "#c0ffee" -b "white" "Some input text"
tco -b "grey" -B "Some input text"

tco "{{alert ERROR:}} The {{::b download}} has failed."
echo "{{#000:#ffffff black on white}}" | tco

For the full list of options, please refer to the help of the tco command.

Specifying colours

With both the Ruby library and the command line tool, there is a number of ways how to specify the colour you would like:

  • RGB - you can do either #c0ffee or 0xc0ffee
  • name - e.g., black or white, you can assign names to colours in your configuration file
  • index - you can also refer to colours through an index to the palette, e.g., @0 or @176.


There are two places, where you can store your configuration:

  • /etc/tco.conf - the system-wide configuration file
  • ~/.tco.conf - user configuration file (takes precedence)

Both of them are simple YAML text files. Pick the first one if you would like to apply your settings system-wide, go with the second option to set things up for yourself only (recommended).

And now the important bit, in order to make tco work best in your environment, it is recommended to configure your ANSI palette. These 16 colours are configurable in most terminals (you probably have yours customised too). tco needs to know your setup, so it can make decisions which colour to use. If you don't configure them, tco will not use the ANSI colours at all in order to avoid mistakes. You can do so like this:

# Don't forget changing the values to match your terminal configuration
    "@0": "#3b3b3b"
    "@1": "#cf6a4c"
    "@2": "#99ad6a"
    "@3": "#d8ad4c"
    "@4": "#597bc5"
    "@5": "#a037b0"
    "@6": "#71b9f8"
    "@7": "#adadad"

    "@8": "#555555"
    "@9": "#ff5555"
    "@10": "#55ff55"
    "@11": "#ffff55"
    "@12": "#5555ff"
    "@13": "#ff55ff"
    "@14": "#55ffff"
    "@15": "#ffffff"

Apart from that you can also create aliases for colours and define short-cut styles for configurations you tend to use often. A typical configuration file would look like this:

# This is unnecessary (extended palette is enabled by default).
# However, you can set this to ansi if you use an older terminal.
    palette: "extended"

    "@0": "#3b3b3b"
    "@1": "#cf6a4c"
    "@2": "#99ad6a"
    "@3": "#d8ad4c"
    # and so on ...

    black: "#000"
    red: "@1"

        fg: "black"
        bg: "red"
        bright: "true"
        underline: "false"


  1. Fork it ( )
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create new Pull Request