From Shopify Wiki

Filters manipulate the output of variables. Filters look like this {{ variablename | filtername }}. For example:

{{ product.title | upcase }}

YOUR PRODUCT TITLE

HTML Filters

• img_tag Wraps element in <img> tag. img_tag(url, alt="")
• script_tag Wraps element in <script> tag
• stylesheet_tag Wraps link in a stylesheet <link> tag

URL Filters

• asset_url Returns the url for an asset.
• global_asset_url Returns the url for a global asset.
• link_to Creates a <a href=""> tag. link_to: 'http://example.com', 'title tag text'
• link_to_vendor Creates a link to the vendor page
• link_to_type Creates a link to the type page
• link_to_tag Creates a link to the tag page
• link_to_theme Generates a link to switch to a different theme by role
• link_to_add_tag Links to products that have the given tag and any previously applied tags
• link_to_remove_tag
• product_img_url Generates a product image's URL for a particular size img_url: 'size'
• collection_img_url Generates a collection image's URL for a particular size img_url: 'size'
• theme_url Generates a URL to switch to a different theme by role
• url_for_vendor Creates an url for a vendor name
• url_for_type Creates an url for type name
• url_for_product Creates an url to a product page based on a handleized product title

Money Filters

• money_with_currency Takes a number and wraps in the currency symbol and descriptor
• money_without_currency Formats the number, but displays no currency symbol or descriptor
• money Converts a number into a string based on your currency

Math Filters

• plus Adding input to operand plus: 10
• minus Subtracting input from operand minus: 10
• times Multiplying input by operand times: 10
• divided_by Dividing input by operand divided_by: 10

Manipulation Filters

• append Append characters to a string
• camelize Converts into CamelCase, strips spaces and irregular characters
• capitalize Capitalizes a string
• date Reformat a date
• default_pagination Use with the paginate liquid tag to create pagination
• downcase Converts a string into lowercase
• escape Escapes a string
• first Get the first element of the passed in array
• handleize Non-word characters are stripped out and characters are lowercased
• highlight_active_tag Creats a span with the class "active"
• join Joins an array with a specified character join: ', '
• last Get the last element in an array
• replace_first Replace the first occurrence of a string with another
• remove Removes all occurrences of the substring from the input remove: 'red'
• remove_first Removes only the first occurrence of the substring from the input remove_first: 'red'
• newline_to_br Inserts a <br /> tag in front of every \n linebreak character.
• pluralize Can make a word plural pluralize: 'item', 'items'
• prepend Append characters to a string
• size Return the size of an array or string
• split Divides a string into substrings based on a delimiter, returning an array of these substrings
• strip_html Striple all html tags from string
• strip_newlines Removes all newlines from the input
• replace Will replace all occurrences of a string with another
• truncate Truncate a string down to x characters
• truncatewords Truncate string down to x words
• upcase Convert a input string to uppercase
• weight_with_unit Converts a weight into the unit system of the shop
• json Converts some content into a JSON string