Module Sass
  1. lib/sass.rb
  2. lib/sass/constant.rb
  3. lib/sass/css.rb
  4. lib/sass/engine.rb
  5. lib/sass/error.rb
  6. lib/sass/plugin.rb

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 two spaces of 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; }

Constants

Sass has support for setting document-wide constants. They‘re set using an exclamation mark followed by the name, an equals sign, and the value. An attribute can then be set to the value of a constant by following it with another equals sign. For example:

  !main_color = #00ff00

  #main
    :color = !main_color
    :p
      :background-color = !main_color
      :color #000000

is compiled to:

  #main {
    color: #00ff00; }
    #main p {
      background-color: #00ff00;
      color: #000000; }

Arithmetic

You can even do basic arithmetic with constants. Sass recognizes numbers, colors, lengths (numbers with units), and strings (everything that‘s not one of the above), and various operators that work on various values. All the normal arithmetic operators (+, -, *, /, %, and parentheses for grouping) are defined as usual for numbers, colors, and lengths. The "+" operator is also defined for Strings as the concatenation operator. For example:

  !main_width = 10
  !unit1 = em
  !unit2 = px
  !bg_color = #a5f39e

  #main
    :background-color = !bg_color
    p
      :background-color = !bg_color + #202020
      :width = !main_width + !unit1
    img.thumb
      :width = (!main_width + 15) + !unit2

is compiled to:

  #main {
    background-color: #a5f39e; }
    #main p {
      background-color: #c5ffbe;
      width: 10em; }
    #main img.thumb {
      width: 25em; }

Colors

Colors may be written as three- or six-digit hex numbers prefixed by a pound sign (#), or as HTML4 color names. For example, "ff0", "ffff00" and "yellow" all refer to the same color.

Not only can arithmetic be done between colors and other colors, but it can be done between colors and normal numbers. In this case, the operation is done piecewise one each of the Red, Green, and Blue components of the color. For example:

  !main_color = #a5f39e

  #main
    :background-color = !main_color
    p
      :background-color = !main_color + 32

is compiled to:

  #main {
    background-color: #a5f39e; }
    #main p {
      background-color: #c5ffbe; }

Strings

Strings are the type that‘s used by default when an element in a bit of constant arithmetic isn‘t recognized as another type of constant. However, they can also be created explicitly be wrapping a section of code with quotation marks. Inside the quotation marks, a backslash can be used to escape quotation marks that you want to appear in the CSS. For example:

  !content = "Hello, \"Hubert\" Bean."

  #main
    :content = "string(" + !content + ")"

is compiled to:

  #main {
    content: string(Hello, "Hubert" Bean.) }

Optional Assignment

You can assign Sass constants if they aren‘t already assigned using the ||= assignment operator. This means that if the constant 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?"

  #main
    content = content

is compiled to:

  #main {
    content: First content; }

However,

  !content ||= "Second content?"

  #main
    content = content

is compiled to:

  #main {
    content: Second content?; }

Default Concatenation

All those plusses and quotes for concatenating strings can get pretty messy, though. Most of the time, if you want to concatenate stuff, you just want individual values with spaces in between them. Thus, in Sass, when two values are next to each other without an operator, they‘re simply joined with a space. For example:

  !font_family = "sans-serif"
  !main_font_size = 1em

  #main
    :font
      :family = !font_family
      :size = !main_font_size
    h6
      :font = italic "small-caps" bold (!main_font_size + 0.1em) !font_family

is compiled to:

  #main {
    font-family: sans-serif;
    font-size: 1em; }
    #main h6 {
      font: italic small-caps bold 1.1em sans-serif; }

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

Import

Currently, the only directive is the "import" directive. It 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 constants 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.

@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; }
  }

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; }

Mixins

Mixins enable you to define groups of CSS attributes and then include them inline in any number of selectors throughout the document.

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 defined earlier in the file. E.g.

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

  =compound
    +highlighted-background
    +header-text

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
The directory where Sass templates should be read from. Defaults to RAILS_ROOT + "/public/stylesheets/sass" or MERB_ROOT + "/public/stylesheets/sass". Only has meaning within Ruby on Rails or Merb.
:css_location
The directory where CSS output should be written to. 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.