Support NO_COLOR environment variable

[mmessmore]

Support disabling color output globally using the NO_COLOR environment variable as specified here: https://no-color.org/

In particular it would be useful for CI output and users who dislike stylized output for my CLIs.

[davidism]

Duplicate of #1498. While I understand the intention of the proposal, it's not clear that it's an actual accepted standard (there are plenty of other env vars across projects), or the correct thing to do. See linked discussions on the previous issue. For example, Click doesn't provide a --color option, so every project would still need to implement turning color back on manually. At that point, why not also do this:

if __name__ == "__main__":
    color = os.environ.get("NO_COLOR")
    color = color in {"1", "true"} if color is not None else None
    cli(color=color)

I did see that Rich implements this, but that alone isn't a convincing reason for it.

[mmessmore]

Sorry, I should have found the prior issue. It really doesn’t need to be supported directly, I guess, but easy to implement support without logic around every style or secho. It may be already. To me, ideally there should be a simple pattern for support or direct support.

And thank you. This library has made me happy and more productive for so long.

[davidism]

No problem.

The color parameter shown above will tell Click to not output color codes. So if you want to support that env var, reading it and setting the parameter will do the right thing.

[kdeldycke]

If you're interested @mmessmore, I've created a ready-to-use --color/--no-color flag option for Click that is supporting the NO_COLOR convention. It is available as a part of click-extra.

[mmessmore]

Oh, thank you. That’s great.