Dart Sass Command-Line Interface

Usage

The Dart Sass executable can be invoked in one of two modes.

One-to-One Mode

sass <input.scss> [output.css]

One-to-one mode compiles a single input file (input.scss) to a single output location (output.css). If no output location is passed, the compiled CSS is printed to the terminal.

The input file is parsed as SCSS if its extension is .scss, as the indented syntax if its extension is .sass, or as plain CSS if its extension is .css. If it doesn’t have one of these three extensions, or if it comes from standard input, it’s parsed as SCSS by default. This can be controlled with the --indented flag.

The special string - can be passed in place of the input file to tell Sass to read the input file from standard input. Sass will default to parsing it as SCSS unless the --indented flag is passed.

Many-to-many Mode

Compatibility:
Dart Sass
since 1.4.0
sass [<input.css>:<output.css>] [<input/>:<output/>]...

Many-to-many mode compiles one or more input files to one or more output files. The inputs are separated from the outputs with colons. It can also compile all Sass files in a directory to CSS files with the same names in another directory.

​# Compiles style.scss to style.css.
$ sass style.scss:style.css

​# Compiles light.scss and dark.scss to light.css and dark.css.
$ sass light.scss:light.css dark.scss:dark.css

​# Compiles all Sass files in themes/ to CSS files in public/css/.
$ sass themes:public/css

When compiling whole directories, Sass will ignore partial files whose names begin with _. You can use partials to separate out your stylesheets without creating a bunch of unnecessary output files.

Options

Input and Output

These options control how Sass loads its input files and how it produces output files.

--stdin

This flag is an alternative way of telling Sass that it should read its input file from standard input. When it’s passed, no input file may be passed.

$ echo "h1 {font-size: 40px}" | sass --stdin h1.css
$ echo "h1 {font-size: 40px}" | sass --stdin
h1 {
  font-size: 40px;
}

The --stdin flag may not be used with many-to-many mode.

--indented

This flag tells Sass to parse the input file as the indented syntax. If it’s used in many-to-many mode, all input files are parsed as the indented syntax, although files they import will have their syntax determined as usual. The inverse, --no-indented, can be used to force all input files to be parsed as SCSS instead.

The --indented flag is mostly useful when the input file is coming from standard input, so its syntax can’t be automatically determined.

$ echo -e 'h1\n  font-size: 40px' | sass --indented -
h1 {
  font-size: 40px;
}

--load-path

This option (abbreviated -I) adds an additional load path for Sass to look for imports. It can be passed multiple times to provide multiple load paths. Earlier load paths will take precedence over later ones.

$ sass --load-path=node_modules/bootstrap/dist/css style.scss style.css

--style

This option (abbreviated -s) controls the output style of the resulting CSS. Dart Sass supports two output styles:

  • expanded (the default) writes each selector and declaration on its own line.
  • compressed removes as many extra characters as possible, and writes the entire stylesheet on a single line.
$ sass --style=expanded style.scss
h1 {
  font-size: 40px;
}

$ sass --style=compressed style.scss
h1{font-size:40px}

--no-charset

Compatibility:
Dart Sass
since 1.19.0

This flag tells Sass never to emit a @charset declaration or a UTF-8 byte-order mark. By default, or if --charset is passed, Sass will insert either a @charset declaration (in expanded output mode) or a byte-order mark (in compressed output mode) if the stylesheet contains any non-ASCII characters.

$ echo 'h1::before {content: "👭"}' | sass --no-charset
h1::before {
  content: "👭";
}

$ echo 'h1::before {content: "👭"}' | sass --charset
@charset "UTF-8";
h1::before {
  content: "👭";
}

--error-css

Compatibility:
Dart Sass
since 1.20.0

This flag tells Sass whether to emit a CSS file when an error occurs during compilation. This CSS file describes the error in a comment and in the content property of body::before, so that you can see the error message in the browser without needing to switch back to the terminal.

By default, error CSS is enabled if you’re compiling to at least one file on disk (as opposed to standard output). You can pass --error-css explicitly to enable it even when you’re compiling to standard out, or --no-error-css to disable it everywhere. When it’s disabled, the --update flag and --watch flag will delete CSS files instead when an error occurs.

$ sass --error-css style.scss style.css
/* Error: Incompatible units em and px.
 *   ,
 * 1 | $width: 15px + 2em;
 *   |         ^^^^^^^^^^
 *   '
 *   test.scss 1:9  root stylesheet */

body::before {
  font-family: "Source Code Pro", "SF Mono", Monaco, Inconsolata, "Fira Mono",
      "Droid Sans Mono", monospace, monospace;
  white-space: pre;
  display: block;
  padding: 1em;
  margin-bottom: 1em;
  border-bottom: 2px solid black;
  content: "Error: Incompatible units em and px.\a   \2577 \a 1 \2502  $width: 15px + 2em;\a   \2502          ^^^^^^^^^^\a   \2575 \a   test.scss 1:9  root stylesheet";         
}
Error: Incompatible units em and px.
  ╷
1 │ $width: 15px + 2em;
  │         ^^^^^^^^^^
  ╵
  test.scss 1:9  root stylesheet

--update

Compatibility:
Dart Sass
since 1.4.0

If the --update flag is passed, Sass will only compile stylesheets whose dependencies have been modified more recently than the corresponding CSS file was generated. It will also print status messages when updating stylesheets.

$ sass --update themes:public/css
Compiled themes/light.scss to public/css/light.css.

Source Maps

Compatibility:
Dart Sass
since 1.3.0

Source maps are files that tell browsers or other tools that consume CSS how that CSS corresponds to the Sass files from which it was generated. They make it possible to see and even edit your Sass files in browsers. See instructions for using source maps in Chrome and Firefox.

Dart Sass generates source maps by default for every CSS file it emits.

--no-source-map

If the --no-source-map flag is passed, Sass won’t generate any source maps. it cannot be passed along with other source map options.

$ sass --no-source-map style.scss style.css

--source-map-urls

This option controls how the source maps that Sass generates link back to the Sass files that contributed to the generated CSS. Dart Sass supports two types of URLs:

  • relative (the default) uses relative URLs from the location of the source map file to the locations of the Sass source file.
  • absolute uses the absolute file: URLs of the Sass source files. Note that absolute URLs will only work on the same computer that the CSS was compiled.
​# Generates a URL like "../sass/style.scss".
$ sass --source-map-urls=relative sass/style.scss css/style.css

​# Generates a URL like "file:///home/style-wiz/sassy-app/sass/style.scss".
$ sass --source-map-urls=absolute sass/style.scss css/style.css

--embed-sources

This flag tells Sass to embed the entire contents of the Sass files that contributed to the generated CSS in the source map. This may produce very large source maps, but it guarantees that the source will be available on any computer no matter how the CSS is served.

$ sass --embed-sources sass/style.scss css.style.css

--embed-source-map

This flag tells Sass to embed the contents of the source map file in the generated CSS, rather than creating a separate file and linking to it from the CSS.

$ sass --embed-source-map sass/style.scss css.style.css

Other Options

--watch

Compatibility:
Dart Sass
since 1.6.0

This flag acts like the --update flag, but after the first round compilation is done Sass stays open and continues compiling stylesheets whenever they or their dependencies change.

$ sass --watch themes:public/css
Compiled themes/light.scss to public/css/light.css.

​# Then when you edit themes/dark.scss...
Compiled themes/dark.scss to public/css/dark.css.

--poll

Compatibility:
Dart Sass
since 1.8.0

This flag, which may only be passed along with --watch, tells Sass to manually check for changes to the source files every so often instead of relying on the operating system to notify it when something changes. This may be necessary if you’re editing Sass on a remote drive where the operating system’s notification system doesn’t work.

$ sass --watch --poll themes:public/css
Compiled themes/light.scss to public/css/light.css.

​# Then when you edit themes/dark.scss...
Compiled themes/dark.scss to public/css/dark.css.

--stop-on-error

Compatibility:
Dart Sass
since 1.8.0

This flag tells Sass to stop compiling immediately when an error is detected, rather than trying to compile other Sass files that may not contain errors. It’s mostly useful in many-to-many mode.

$ sass --stop-on-error themes:public/css
Error: Expected expression.
   ╷
42 │ h1 {font-face: }
   │                ^
   ╵
  themes/light.scss 42:16  root stylesheet

--interactive

Compatibility:
Dart Sass
since 1.5.0

This flag (abbreviated -i) tells Sass to run in interactive mode, where you can write SassScript expressions and see their results. Interactive mode also supports variables.

$ sass --interactive
>> 1px + 1in
97px
>> $map: ("width": 100px, "height": 70px)
("width": 100px, "height": 70px)
>> map-get($map, "width")
100px

--color

This flag (abbreviated -c) tells Sass to emit terminal colors, and the inverse --no-color tells it not to emit colors. By default, it will emit colors if it looks like it’s being run on a terminal that supports them.

$ sass --color style.scss style.css
Error: Incompatible units em and px.
  
1 │ $width: 15px + 2em
           ^^^^^^^^^^
  
  style.scss 1:9  root stylesheet

$ sass --no-color style.scss style.css
Error: Incompatible units em and px.
  ╷
1 │ $width: 15px + 2em
  │         ^^^^^^^^^^
  ╵
  style.scss 1:9  root stylesheet

--no-unicode

Compatibility:
Dart Sass
since 1.17.0

This flag tells Sass only to emit ASCII characters to the terminal as part of error messages. By default, or if --unicode is passed, Sass will emit non-ASCII characters for these messages. This flag does not affect the CSS output.

$ sass --no-unicode style.scss style.css
Error: Incompatible units em and px.
  ,
1 | $width: 15px + 2em;
  |         ^^^^^^^^^^
  '
  test.scss 1:9  root stylesheet

$ sass --unicode style.scss style.css
Error: Incompatible units em and px.
  ╷
1 │ $width: 15px + 2em;
  │         ^^^^^^^^^^
  ╵
  test.scss 1:9  root stylesheet

--quiet

This flag (abbreviated -q) tells Sass not to emit any warnings when compiling. By default, Sass emits warnings when deprecated features are used or when the @warn rule is encountered. It also silences the @debug rule.

$ sass --quiet style.scss style.css

--trace

This flag tells Sass to print the full Dart or JavaScript stack trace when an error is encountered. It’s used by the Sass team for debugging errors.

$ sass --trace style.scss style.css
Error: Expected expression.
   ╷
42 │ h1 {font-face: }
   │                ^
   ╵
  themes/light.scss 42:16  root stylesheet

package:sass/src/visitor/evaluate.dart 1846:7                        _EvaluateVisitor._addExceptionSpan
package:sass/src/visitor/evaluate.dart 1128:12                       _EvaluateVisitor.visitBinaryOperationExpression
package:sass/src/ast/sass/expression/binary_operation.dart 39:15     BinaryOperationExpression.accept
package:sass/src/visitor/evaluate.dart 1097:25                       _EvaluateVisitor.visitVariableDeclaration
package:sass/src/ast/sass/statement/variable_declaration.dart 50:15  VariableDeclaration.accept
package:sass/src/visitor/evaluate.dart 335:13                        _EvaluateVisitor.visitStylesheet
package:sass/src/visitor/evaluate.dart 323:5                         _EvaluateVisitor.run
package:sass/src/visitor/evaluate.dart 81:10                         evaluate
package:sass/src/executable/compile_stylesheet.dart 59:9             compileStylesheet
package:sass/src/executable.dart 62:15                               main

--help

This flag (abbreviated -h) prints a summary of this documentation.

$ sass --help
Compile Sass to CSS.

Usage: sass <input.scss> [output.css]
       sass <input.scss>:<output.css> <input/>:<output/>

...

--version

This flag prints the current version of Sass.

$ sass --version
1.20.1