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I think overriding use_color (NO_COLOR) based on tty is not a good idea. Because we override it, we also need a new env var FORCE_COLOR here, and having two env vars both controlling color is confusing.

Do you think it is better to have different functions use_color and is_tty and check directly in the main? Or do you think it is better to add a new variable in bootstrap options called is_tty?

Do you think it is better to have different functions use_color and is_tty and check directly in the main? Or do you think it is better to add a new variable in bootstrap options called is_tty?

I think we need both. First check IS_TTY and store its value (you already did it), and expose it as is_tty function. The main module checks is_tty function and pass it as bootstrap option next to noColor option (You need to extend BootstrapOptions struct). Finally set the no color option of console module to noColor || !isTty in runtime/js/99_main.js script ref:

BTW you can test this behavior by passing stdout: "piped" options to Deno.run command.

const p = Deno.run({
  cmd: [
    Deno.execPath(),
    "eval",
    "console.log(1)",
  ],
  stdout: "piped",
});
const output = await p.output();

This should make is_tty = false

I put the test, I don't know if it is the right place. Let me know!

I don't know if ci / test release ubuntu-20.04-xl fail because I miss to add in test { permissions: { run: true } }

The test case looks good to me. Nice work!