[v4] Capturing STDOUT in v4?

[vormwald]

Hey! I have a jekyll plugin that captures output from Tailwind CLI (using executable in the tailwindcss-ruby gem). Using the current 3.4 With a typical setup, it's essentially running:

npx [email protected] -i ./input.css 

Which will print generated CSS to stdout.

I've been trying to recreate this behavior with v4 and have noticed something odd.

Running the command I did before no longer works:

" NOTE input.css contents are now:  @import "tailwindcss";

〉 npx @tailwindcss/cli@next --input ./input.css
≈ tailwindcss v4.0.0-beta.6

Usage:
  tailwindcss [--input input.css] [--output output.css] [--watch] [options…]

Options:
  -i, --input ··········· Input file
  -o, --output ·········· Output file
  -w, --watch ··········· Watch for changes and rebuild as needed
  -m, --minify ·········· Optimize and minify the output
      --optimize ········ Optimize the output without minifying
      --cwd ············· The current working directory [default: `.`]
  -h, --help ············ Display usage information

So I add the --output option...

〉 npx @tailwindcss/cli@next --input ./tailwind.css --output
≈ tailwindcss v4.0.0-beta.6

Done in 256ms

Which does something surprising. It creates a new file, ./true that contains generated CSS.

〉 head ./true
/*! tailwindcss v4.0.0-beta.6 | MIT License | https://tailwindcss.com */
@layer theme, base, components, utilities;
@layer theme {
  :root {
    --font-sans: ui-sans-serif, system-ui, sans-serif, "Apple Color Emoji",
      "Segoe UI Emoji", "Segoe UI Symbol", "Noto Color Emoji";
    --font-serif: ui-serif, Georgia, Cambria, "Times New Roman", Times, serif;
    --font-mono: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas,
      "Liberation Mono", "Courier New", monospace;
    --color-red-50: oklch(0.971 0.013 17.38);

I wanted to raise this as a potential issue and also check my expectation that stdout capture is still available in v4+

Thanks all for the hard work <3

[vormwald]

I'm seeing the same behavior with beta 8 if that helps.

[vormwald]

This issue was raised in #15648 and addressed in #15656