Ruby Sass CLI

What You’ll Learn

The Ruby Sass CLI was the original sass gem command line. This page explains how it worked (modes, styles, watch, source maps), how it differs from Dart Sass, and how to migrate—with five reference examples from the official docs.

What Was the Ruby Sass CLI?

Ruby Sass shipped a sass executable (from the Ruby gem) that compiled .scss / .sass files to CSS. Like Dart Sass today, it had one-to-one and many-to-many modes, watch/update flags, and style options.

• It is unmaintained—no security or language updates.
• Default stdin / unknown extensions used the indented syntax (Dart Sass defaults to SCSS).
• It offered four --style values; Dart Sass keeps two.
• Features like --compass and --require tied it to the Ruby ecosystem.

📄 One-to-One Mode

sass [input.scss] [output.css]

Compiled one input to one output. No output path printed CSS to the terminal. No input or output meant read from stdin and print CSS. Extensions: .scss → SCSS, .sass → indented. Otherwise (and for stdin), indented was the default—use --scss to force SCSS.

📦 Many-to-Many Mode

Enabled when any argument contains a colon, or when --update / --watch is passed. Directory compiles skipped _partials. Unlike a pure one-shot Dart folder compile, Ruby many-to-many also behaved like an update: it compiled only when sources were newer than the CSS.

sass style.scss:style.css
sass light.scss:light.css dark.scss:dark.css
sass themes:public/css

⚖️ Ruby Sass CLI vs Dart Sass CLI

⚙️ Important Legacy Options

🚀 Migrate to Dart Sass

1. Install Dart Sass (Installation).
2. Replace gem install sass / Bundler sass gem with the Dart sass CLI or npm package.
3. Update scripts: map --style=compressed as before; drop nested/compact or switch to expanded.
4. For stdin SCSS, you usually do not need a flag (Dart default); use --indented only for indented input.
5. Retest builds; fix any language differences and prefer @use over legacy @import.

Examples Gallery

Reference examples from the official Ruby Sass CLI docs. Do not install Ruby Sass for new work—compare with Dart Sass after you migrate.

h1 {
  font-size: 40px;
}

sass style.scss style.css
sass style.scss          # print CSS to the terminal

h1 {
  font-size: 40px;
}

sass themes:public/css
#      write public/css/light.css
#      write public/css/light.css.map
#      write public/css/dark.css
#      write public/css/dark.css.map

- Partials (_file.scss) were not emitted as CSS
- Only outdated files were rewritten (update-style)
- Prefer: sass themes:public/css  (Dart Sass)

sass --style=nested style.scss
sass --style=expanded style.scss
sass --style=compact style.scss
sass --style=compressed style.scss

h1{font-size:40px}h1 code{font-face:Roboto Mono}

echo "h1 {font-size: 40px}" | sass --scss

h1 {
  font-size: 40px;
}

sass --watch themes:public/css
#      write public/css/light.css
#      write public/css/light.css.map
# After editing themes/dark.scss...
#      write public/css/dark.css
#      write public/css/dark.css.map

sass --watch --poll themes:public/css   # remote drives
sass --update style.scss                # many-to-many without colon

sass --watch themes:public/css
sass --update themes:public/css

🚀 When This Page Still Helps

• Reading legacy CI — decode old sass --style=compact scripts.
• Migrating Rails / Compass apps — replace gem + --compass setups.
• Interview / history — know why Ruby Sass existed and why it stopped.
• Flag translation — map --sourcemap=none → --no-source-map.
• Teaching — contrast EOL tools with the maintained Dart Sass CLI.

⚠️ Common Pitfalls

• Installing Ruby Sass “just to learn” — learn Dart Sass instead.
• Assuming stdin is SCSS — Ruby defaulted to indented; Dart defaults to SCSS.
• Copying nested/compact — not available on Dart Sass.
• Keeping --compass forever — replace with modern packages / CSS.
• Mixing docs — Ruby flag letters differ (-t style vs Dart -s).

💡 Best Practices