CLIs don't always make it clear when an action has taken place. For every
action a user performs, your CLI should provide an equal and appropriate
reaction, clearly highlighting the what just happened. For example:

```shell
$ nix build
 Downloaded python3.8-poetry 1.2.3 in 5.3 seconds
 Downloaded python3.8-requests 1.2.3 in 5.3 seconds
...
   Success! You have successfully built my-project.
$
```

Above command clearly states that command successfully completed. And in case
of `nix build`, which is a command that might take some time to complete, it is
equally important to also show that a command started.

## Text alignment

Text alignment is the number one design element that will present all of the
Nix commands as a family and not as separate tools glued together.

The format we should follow is:

```shell
$ nix COMMAND
   VERB_1 NOUN and other words
  VERB__1 NOUN and other words
       |> Some details
```

Few rules that we can extract from above example:

- Each line should start at least with one space.
- First word should be a VERB and must be aligned to the right.
- Second word should be a NOUN and must be aligned to the left.
- If you can not find a good VERB / NOUN pair, don’t worry make it as
  understandable to the user as possible.
- More details of each line can be provided by `|>` character which is serving
  as the first word when aligning the text

Don’t forget you should also test your terminal output with colors and emojis
off (`--no-colors --no-emojis`).

## Dim / Bright

After comparing few terminals with different color schemes we would **recommend
to avoid using dimmed text**. The difference from the rest of the text is very
little in many terminal and color scheme combinations. Sometimes the difference
is not even notable, therefore relying on it wouldn’t make much sense.

**The bright text is much better supported** across terminals and color
schemes. Most of the time the difference is perceived as if the bright text
would be bold.

## Colors

Humans are already conditioned by society to attach certain meaning to certain
colors. While the meaning is not universal, a simple collection of colors is
used to represent basic emotions.

Colors that can be used in output

- Red = error, danger, stop
- Green = success, good
- Yellow/Orange = proceed with caution, warning, in progress
- Blue/Magenta = stability, calm

While colors are nice, when command line is used by machines (in automation
scripts) you want to remove the colors. There should be a global `--no-colors`
option that would remove the colors.

## Special (Unicode) characters

Most of the terminal have good support for Unicode characters and you should
use them in your output by default. But always have a backup solution that is
implemented only with ASCII characters and will be used when `--ascii` option
is going to be passed in. Please make sure that you test your output also
without Unicode characters

More they showing all the different Unicode characters it is important to
**establish common set of characters** that we use for certain situations.

## Emojis

Emojis help channel emotions even better than text, colors and special
characters.

We recommend **keeping the set of emojis to a minimum**. This will enable each
emoji to stand out more.

As not everybody is happy about emojis we should provide an `--no-emojis`
option to disable them. Please make sure that you test your output also without
emojis.