Module: Sass

Extended by:

Haml::Version

Defined in:

lib/sass.rb,
lib/sass/css.rb,
lib/sass/repl.rb,
lib/sass/error.rb,
lib/sass/engine.rb,
lib/sass/plugin.rb,
lib/sass/script.rb,
lib/sass/tree/node.rb,
lib/sass/environment.rb,
lib/sass/script/lexer.rb,
lib/sass/script/parser.rb,
lib/sass/script/funcall.rb,
lib/sass/tree/file_node.rb,
lib/sass/script/variable.rb,
lib/sass/tree/debug_node.rb,
lib/sass/tree/variable_node.rb,
lib/sass/tree/mixin_def_node.rb

Overview

Sass (Syntactically Awesome StyleSheets)

Sass is a meta-language on top of CSS that’s used to describe the style of a document cleanly and structurally, with more power than flat CSS allows. Sass both provides a simpler, more elegant syntax for CSS and implements various features that are useful for creating manageable stylesheets.

Features

• Whitespace active

• Well-formatted output

• Elegant input

• Feature-rich

Using Sass

Sass can be used in three ways: as a plugin for Ruby on Rails, as a standalone Ruby module, and as a command-line tool. Sass is bundled with Haml, so if the Haml plugin or RubyGem is installed, Sass will already be installed as a plugin or gem, respectively. The first step for all of these is to install the Haml gem:

gem install haml

To enable it as a Rails plugin, then run

haml --rails path/to/rails/app

To enable Sass in Merb, add

dependency "merb-haml"

to config/dependencies.rb.

Sass templates in Rails don’t quite function in the same way as views, because they don’t contain dynamic content, and so only need to be compiled when the template file has been updated. By default (see options, below), “.sass” files are placed in public/stylesheets/sass. Then, whenever necessary, they’re compiled into corresponding CSS files in public/stylesheets. For instance, public/stylesheets/sass/main.sass would be compiled to public/stylesheets/main.css.

To run Sass from the command line, just use

sass input.sass output.css

Use sass --help for full documentation.

Using Sass in Ruby code is very simple. After installing the Haml gem, you can use it by running require "sass" and using Sass::Engine like so:

engine = Sass::Engine.new("#main\n  :background-color #0000ff")
engine.render #=> "#main { background-color: #0000ff; }\n"

CSS Rules

Rules in flat CSS have two elements: the selector (e.g. “#main”, “div p”, “li a:hover”) and the attributes (e.g. “color: #00ff00;”, “width: 5em;”).

Sass has both of these, as well as one additional element: nested rules.

Rules and Selectors

However, some of the syntax is a little different. The syntax for selectors is the same, but instead of using brackets to delineate the attributes that belong to a particular rule, Sass uses indentation. For example:

#main p
  <attribute>
  <attribute>
  ...

Like CSS, you can stretch rules over multiple lines. However, unlike CSS, you can only do this if each line but the last ends with a comma. For example:

.users #userTab,
.posts #postsTab
  <attributes>

Attributes

There are two different ways to write CSS attrbibutes. The first is very similar to the how you’re used to writing them: with a colon between the name and the value. However, Sass attributes don’t have semicolons at the end; each attribute is on its own line, so they aren’t necessary. For example:

#main p
  color: #00ff00
  width: 97%

is compiled to:

#main p {
  color: #00ff00;
  width: 97% }

The second syntax for attributes is slightly different. The colon is at the beginning of the attribute, rather than between the name and the value, so it’s easier to tell what elements are attributes just by glancing at them. For example:

#main p
  :color #00ff00
  :width 97%

is compiled to:

#main p {
  color: #00ff00;
  width: 97% }

By default, either attribute syntax may be used. If you want to force one or the other, see the :attribute_syntax option below.

Nested Rules

Rules can also be nested within each other. This signifies that the inner rule’s selector is a child of the outer selector. For example:

#main p
  :color #00ff00
  :width 97%

  .redbox
    :background-color #ff0000
    :color #000000

is compiled to:

#main p {
  color: #00ff00;
  width: 97%; }
  #main p .redbox {
    background-color: #ff0000;
    color: #000000; }

This makes insanely complicated CSS layouts with lots of nested selectors very simple:

#main
  :width 97%

  p, div
    :font-size 2em
    a
      :font-weight bold

  pre
    :font-size 3em

is compiled to:

#main {
  width: 97%; }
  #main p, #main div {
    font-size: 2em; }
    #main p a, #main div a {
      font-weight: bold; }
  #main pre {
    font-size: 3em; }

Referencing Parent Rules

In addition to the default behavior of inserting the parent selector as a CSS parent of the current selector (e.g. above, “#main” is the parent of “p”), you can have more fine-grained control over what’s done with the parent selector by using the ampersand character “&” in your selectors.

The ampersand is automatically replaced by the parent selector, instead of having it prepended. This allows you to cleanly create pseudo-attributes:

a
  :font-weight bold
  :text-decoration none
  &:hover
    :text-decoration underline
  &:visited
    :font-weight normal

Which would become:

a {
  font-weight: bold;
  text-decoration: none; }
  a:hover {
    text-decoration: underline; }
  a:visited {
    font-weight: normal; }

It also allows you to add selectors at the base of the hierarchy, which can be useuful for targeting certain styles to certain browsers:

#main
  :width 90%
  #sidebar
    :float left
    :margin-left 20%
    .ie6 &
      :margin-left 40%

Which would become:

#main {
  width: 90%; }
  #main #sidebar {
    float: left;
    margin-left: 20%; }
    .ie6 #main #sidebar {
      margin-left: 40%; }

Attribute Namespaces

CSS has quite a few attributes that are in “namespaces;” for instance, “font-family,” “font-size,” and “font-weight” are all in the “font” namespace. In CSS, if you want to set a bunch of attributes in the same namespace, you have to type it out each time. Sass offers a shortcut for this: just write the namespace one, then indent each of the sub-attributes within it. For example:

.funky
  :font
    :family fantasy
    :size 30em
    :weight bold

is compiled to:

.funky {
  font-family: fantasy;
  font-size: 30em;
  font-weight: bold; }

Rule Escaping

In case, for whatever reason, you need to write a rule that begins with a Sass-meaningful character, you can escape it with a backslash (<tt></tt>). For example:

#main
  \+div
    clear: both

is compiled to:

#main +div {
  clear: both; }

Directives

Directives allow the author to directly issue instructions to the Sass compiler. They’re prefixed with an at sign, “@”, followed by the name of the directive, a space, and any arguments to it - just like CSS directives. For example:

@import red.sass

Some directives can also control whether or how many times a chunk of Sass is output. Those are documented under Control Structures.

import

The “@import” directive works in a very similar way to the CSS import directive, and sometimes compiles to a literal CSS “@import”.

Sass can import either other Sass files or plain CSS files. If it imports a Sass file, not only are the rules from that file included, but all variables in that file are made available in the current file.

Sass looks for other Sass files in the working directory, and the Sass file directory under Rails or Merb. Additional search directories may be specified using the :load_paths option (see below).

Sass can also import plain CSS files. In this case, it doesn’t literally include the content of the files; rather, it uses the built-in CSS “@import” directive to tell the client program to import the files.

The import directive can take either a full filename or a filename without an extension. If an extension isn’t provided, Sass will try to find a Sass file with the given basename in the load paths, and, failing that, will assume a relevant CSS file will be available.

For example,

@import foo.sass

would compile to

.foo
  :color #f00

whereas

@import foo.css

would compile to

@import foo.css

Finally,

@import foo

might compile to either, depending on whether a file called “foo.sass” existed.

@debug

The “@debug” directive prints the value of a SassScript expression to standard error. It’s useful for debugging Sass files that have complicated SassScript going on. For example:

@debug 10em + 12em

outputs:

Line 1 DEBUG: 22em

@font-face, @media, etc.

Sass behaves as you’d expect for normal CSS @-directives. For example:

@font-face
  font-family: "Bitstream Vera Sans"
  src: url(http://foo.bar/bvs")

compiles to:

@font-face {
  font-family: "Bitstream Vera Sans";
  src: url(http://foo.bar/bvs"); }

and

@media print
  #sidebar
    display: none

  #main
    background-color: white

compiles to:

@media print {
  #sidebar {
    display: none; }

  #main {
    background-color: white; }
}

SassScript

In addition to the declarative templating system, Sass supports a simple language known as SassScript for dynamically computing CSS values and controlling the styles and selectors that get emitted.

Interactive Shell

You can easily experiment with SassScript using the interactive shell. To launch the shell run the sass command-line with the -i option. At the prompt, enter any legal SassScript expression to have it evaluated and the result printed out for you:

$ sass -i
>> "Hello, Sassy World!"
"Hello, Sassy World!"
>> 1px + 1px + 1px
3px
>> #777 + #777
#eeeeee
>> #777 + #888
white

Variables

The most straightforward way to use SassScript is to set and reference variables. Variables begin with exclamation marks, and are set like so:

!width = 5em

You can then refer to them by putting an equals sign after your attributes:

#main
  :width = !width

Variables that are first defined in a scoped context are only available in that context.

Data Types

SassScript supports four data types:

• numbers (e.g. 1.2, 13, 10px)

• strings of text (e.g. "foo", "bar")

• colors (e.g. blue, ##04a3f9)

• booleans (e.g. true, false)

Any text that doesn’t fit into one of those types in a SassScript context will cause an error:

p
  !width = 5em
  // This will cause an error
    :border = !width solid blue
  // Use one of the following forms instead:
  :border = "#{!width} solid blue"
  :border = !width "solid" "blue"

is compiled to:

p {
  border: 5em solid blue;
  border: 5em solid blue; }

Operations

SassScript supports the standard arithmetic operations on numbers (+, -, *, /, %), and will automatically convert between units if it can:

p
  :width = 1in + 8pt

is compiled to:

p {
  width: 1.111in; }

Relational operators (<, >, <=, >=) are also supported for numbers, and equality operators (==, !=) are supported for all types.

Most arithmetic operations are supported for color values, where they work piecewise:

p
  :color = #010203 + #040506

is compiled to:

p {
  color: #050709; }

Some arithmetic operations even work between numbers and colors:

p
  :color = #010203 * 2

is compiled to:

p {
  color: #020406; }

The + operation can be used to concatenate strings:

p
  :cursor = "e" + "-resize"

is compiled to:

p {
  cursor: e-resize; }

Within a string of text, #{} style interpolation can be used to place dynamic values within the string:

p
  :border = "#{5px + 10pt} solid #ccc"

Finally, SassScript supports and, or, and not operators for boolean values.

Parentheses

Parentheses can be used to affect the order of operations:

p
  :width = 1em + (2em * 3)

is compiled to:

p {
  width: 7em; }

Functions

SassScript defines some useful functions that are called using the normal CSS function syntax:

p
  :color = hsl(0, 100%, 50%)

is compiled to:

#main {
  color: #ff0000; }

The following functions are provided: hsl, percentage, round, ceil, floor, and abs. You can define additional functions in ruby.

See Sass::Script::Functions for more information.

Interpolation

You can also use SassScript variables in selectors and attribute names using #{} interpolation syntax:

!name = foo
!attr = border
p.#{!name}
  #{attr}-color: blue

is compiled to:

p.foo {
  border-color: blue; }

Optional Assignment

You can assign to variables if they aren’t already assigned using the ||= assignment operator. This means that if the variable has already been assigned to, it won’t be re-assigned, but if it doesn’t have a value yet, it will be given one.

For example:

!content = "First content"
!content ||= "Second content?"
!new_content ||= "First time reference"

#main
  content = !content
  new-content = !new_content

is compiled to:

#main {
  content: First content;
  new-content: First time reference; }

Control Structures

SassScript supports basic control structures for looping and conditionals using the same syntax as directives.

if

The “@if” statement takes a SassScript expression and prints the code nested beneath it if the expression returns anything other than false:

p
  @if 1 + 1 == 2
    :border 1px solid
  @if 5 < 3
    :border 2px dotted

is compiled to:

p {
  border: 1px solid; }

The “@if” statement can be followed by several “@else if” statements and one “@else” statement. If the “@if” statement fails, the “@else if” statements are tried in order until one succeeds or the “@else” is reached. For example:

!type = "monster"
p
  @if !type == "ocean"
    :color blue
  @else if !type == "matador"
    :color red
  @else if !type == "monster"
    :color green
  @else
    :color black

is compiled to:

p {
  color: green; }

for

The “@for” statement has two forms: “@for <var> from <start> to <end>” or “@for <var> from <start> through <end>”. <var> is a variable name, like !i, and <start> and <end> are SassScript expressions that should return integers.

The “@for” statement sets <var> to each number from <start> to <end>, including <end> if “through” is used. For example:

@for !i from 1 through 3
  .item-#{!i}
    :width = 2em * !i

is compiled to:

.item-1 {
  width: 2em; }
.item-2 {
  width: 4em; }
.item-3 {
  width: 6em; }

while

The “@while” statement repeatedly loops over the nested block until the statement evaluates to false. This can be used to achieve more complex looping than the @for statement is capable of. For example:

!i = 6
@while !i > 0
  .item-#{!i}
    :width = 2em * !i
  !i = !i - 2

is compiled to:

.item-6 {
  width: 12em; }

.item-4 {
  width: 8em; }

.item-2 {
  width: 4em; }

Mixins

Mixins enable you to define groups of CSS attributes and then include them inline in any number of selectors throughout the document. This allows you to keep your stylesheets DRY and also avoid placing presentation classes in your markup.

Defining a Mixin

To define a mixin you use a slightly modified form of selector syntax. For example the ‘large-text’ mixin is defined as follows:

=large-text
  :font
    :family Arial
    :size 20px
    :weight bold
  :color #ff0000

The initial ‘=’ marks this as a mixin rather than a standard selector. The CSS rules that follow won’t be included until the mixin is referenced later on. Anything you can put into a standard selector, you can put into a mixin definition. e.g.

=clearfix
  display: inline-block
  &:after
    content: "."
    display: block
    height: 0
    clear: both
    visibility: hidden
  * html &
    height: 1px

Mixing it in

Inlining a defined mixin is simple, just prepend a ‘+’ symbol to the name of a mixin defined earlier in the document. So to inline the ‘large-text’ defined earlier, we include the statment ‘+large-text’ in our selector definition thus:

.page-title
  +large-text
  :padding 4px
  :margin
    :top 10px

This will produce the following CSS output:

.page-title {
  font-family: Arial;
  font-size: 20px;
  font-weight: bold;
  color: #ff0000;
  padding: 4px;
  margin-top: 10px;
}

Any number of mixins may be defined and there is no limit on the number that can be included in a particular selector.

Mixin definitions can also include references to other mixins. E.g.

=compound
  +highlighted-background
  +header-text

=highlighted-background
  background:
    color: #fc0
=header-text
  font:
    size: 20px

Mixins that only define descendent selectors, can be safely mixed into the top most level of a document.

Arguments

Mixins can take arguments which can be used with SassScript:

=sexy-border(!color)
  :border
    :color = !color
    :width 1in
    :style dashed
p
  +sexy-border("blue")

is compiled to:

p {
  border-color: #0000ff;
  border-width: 1in;
  border-style: dashed; }

Mixins can also specify default values for their arguments:

=sexy-border(!color, !width = 1in)
  :border
    :color = !color
    :width = !width
    :style dashed
p
  +sexy-border("blue")

is compiled to:

p {
  border-color: #0000ff;
  border-width: 1in;
  border-style: dashed; }

Comments

Silent Comments

It’s simple to add “silent” comments, which don’t output anything to the CSS document, to a Sass document. Simply use the familiar C-style notation for a one-line comment, “//”, at the normal indentation level and all text following it won’t be output. For example:

// A very awesome rule.
#awesome.rule
  // An equally awesome attribute.
  :awesomeness very

becomes

#awesome.rule {
  awesomeness: very; }

You can also nest text beneath a comment to comment out a whole block. For example:

// A very awesome rule
#awesome.rule
  // Don't use these attributes
    color: green
    font-size: 10em
  color: red

becomes

#awesome.rule {
  color: red; }

Loud Comments

“Loud” comments are just as easy as silent ones. These comments output to the document as CSS comments, and thus use the same opening sequence: “/*”. For example:

/* A very awesome rule.
#awesome.rule
  /* An equally awesome attribute.
  :awesomeness very

becomes

/* A very awesome rule. */
#awesome.rule {
  /* An equally awesome attribute. */
  awesomeness: very; }

You can also nest content beneath loud comments. For example:

#pbj
  /* This rule describes
    the styling of the element
    that represents
    a peanut butter and jelly sandwich.
  :background-image url(/images/pbj.png)
  :color red

becomes

#pbj {
  /* This rule describes
   * the styling of the element
   * that represents
   * a peanut butter and jelly sandwich. */
  background-image: url(/images/pbj.png);
  color: red; }

Output Style

Although the default CSS style that Sass outputs is very nice, and reflects the structure of the document in a similar way that Sass does, sometimes it’s good to have other formats available.

Sass allows you to choose between three different output styles by setting the :style option. In Rails, this is done by setting Sass::Plugin.options[:style]; outside Rails, it’s done by passing an options hash with </tt>:style</tt> set.

:nested

Nested style is the default Sass style, because it reflects the structure of the document in much the same way Sass does. Each attribute has its own line, but the indentation isn’t constant. Each rule is indented based on how deeply it’s nested. For example:

#main {
  color: #fff;
  background-color: #000; }
  #main p {
    width: 10em; }

.huge {
  font-size: 10em;
  font-weight: bold;
  text-decoration: underline; }

Nested style is very useful when looking at large CSS files for the same reason Sass is useful for making them: it allows you to very easily grasp the structure of the file without actually reading anything.

:expanded

Expanded is the typical human-made CSS style, with each attribute and rule taking up one line. Attributes are indented within the rules, but the rules aren’t indented in any special way. For example:

#main {
  color: #fff;
  background-color: #000;
}
#main p {
  width: 10em;
}

.huge {
  font-size: 10em;
  font-weight: bold;
  text-decoration: underline;
}

:compact

Compact style, as the name would imply, takes up less space than Nested or Expanded. However, it’s also harder to read. Each CSS rule takes up only one line, with every attribute defined on that line. Nested rules are placed next to each other with no newline, while groups of rules have newlines between them. For example:

#main { color: #fff; background-color: #000; }
#main p { width: 10em; }

.huge { font-size: 10em; font-weight: bold; text-decoration: underline; }

:compressed

Compressed style takes up the minimum amount of space possible, having no whitespace except that necessary to separate selectors and a newline at the end of the file. It’s not meant to be human-readable. For example:

#main{color:#fff;background-color:#000}#main p{width:10em}.huge{font-size:10em;font-weight:bold;text-decoration:underline}

Sass Options

Options can be set by setting the Sass::Plugin.options hash in environment.rb in Rails…

Sass::Plugin.options[:style] = :compact

…or by setting the Merb::Plugin.config[:sass] hash in init.rb in Merb…

Merb::Plugin.config[:sass][:style] = :compact

…or by passing an options hash to Sass::Engine.new. Available options are:

:style

Sets the style of the CSS output. See the section on Output Style, above.

:attribute_syntax

Forces the document to use one syntax for attributes. If the correct syntax isn’t used, an error is thrown. :normal forces the use of a colon before the attribute name. For example: :color #0f3 or :width = !main_width. :alternate forces the use of a colon or equals sign after the attribute name. For example: color: #0f3 or width = !main_width. By default, either syntax is valid.

:never_update

Whether the CSS files should never be updated, even if the template file changes. Setting this to true may give small performance gains. It always defaults to false. Only has meaning within Ruby on Rails or Merb.

:always_update

Whether the CSS files should be updated every time a controller is accessed, as opposed to only when the template has been modified. Defaults to false. Only has meaning within Ruby on Rails or Merb.

:always_check

Whether a Sass template should be checked for updates every time a controller is accessed, as opposed to only when the Rails server starts. If a Sass template has been updated, it will be recompiled and will overwrite the corresponding CSS file. Defaults to false in production mode, true otherwise. Only has meaning within Ruby on Rails or Merb.

:full_exception

Whether an error in the Sass code should cause Sass to provide a detailed description. If set to true, the specific error will be displayed along with a line number and source snippet. Otherwise, a simple uninformative error message will be displayed. Defaults to false in production mode, true otherwise. Only has meaning within Ruby on Rails or Merb.

:template_location

A path to the root sass template directory for you application. If a hash, :css_location is ignored and this option designates both a mapping between input and output directories. May also be given a list of 2-element lists, instead of a hash. Defaults to RAILS_ROOT + "/public/stylesheets/sass" or MERB_ROOT + "/public/stylesheets/sass". Only has meaning within Ruby on Rails or Merb. This will be derived from the :css_location path list if not provided by appending a folder of “sass” to each corresponding css location.

:css_location

The path where CSS output should be written to. This option is ignored when :template_location is a Hash. Defaults to RAILS_ROOT + "/public/stylesheets" or MERB_ROOT + "/public/stylesheets". Only has meaning within Ruby on Rails or Merb.

:filename

The filename of the file being rendered. This is used solely for reporting errors, and is automatically set when using Rails or Merb.

:load_paths

An array of filesystem paths which should be searched for Sass templates imported with the “@import” directive. This defaults to the working directory and, in Rails or Merb, whatever :template_location is.

:line_numbers

When set to true, causes the line number and file where a selector is defined to be emitted into the compiled CSS as a comment. Useful for debugging especially when using imports and mixins.

Defined Under Namespace

Modules: Plugin, Repl, Script, Tree Classes: CSS, Engine, Environment, Mixin, OrderedHash, SyntaxError

Constant Summary

VERSION =

A string representing the version of Sass. A more fine-grained representation is available from Sass.version.

version[:string]

MERB_LOADED =

true

RAILS_LOADED =

true

Method Summary

Methods included from Haml::Version

scope, version