Variable filters

By default, bindings are inserted into the output as-is; no consideration is given as to whether the target variable or file is XML, HTML, JSON etc. That is, the target file type is always treated as plain text.

Octopus variable substitutions support filters to correctly encode values for a variety of target file types. These are invoked using the | (pipe) operator.

Given the variable:

And the template:

<h3>#{ProjectName | HtmlEscape}</h3>

The result will be:

<h3>You &amp; I</h3>

That is, the ampersand has been encoded correctly for use in an HTML document.

Provided filters

Octopus provides a number of different types of filters for variable values:

• Core filters
• Comparison filters
• Conversion filters
• Date filters
• Escaping filters
• Extraction filters

Core filters

These core filters perform common string operations.

Format

The Format filter allows for converting of input based on an additionally provided argument that is passed to the .ToString() method.

Replace

The Replace filter performs a regular expression replace function on the variable. The regular expression should be provided in the .NET Framework format. Double quotes need to be used around any expressions that contain whitespace or special characters. Expressions containing double quotes can not be expressed inline, but can be done via nested variables. If both the search and replace expressions are variables, ensure there is no space between the expressions. For using Replace on special characters, you should escape the first parameter which will be the regex but the second parameter can be left as a string - see last example below.

Substring

The Substring filter extracts a range of characters from the input and outputs them. If two arguments are supplied, they are interpreted as start and end offsets of the range. If only one argument is supplied, it is interpreted as the end offset of a range starting at 0.

Trim

The Trim filter removes any whitespace from the ends of the input. Both ends are trimmed unless an optional argument of start or end is provided.

Truncate

The Truncate filter limits the length of the input. If the input is longer than the length specified by the argument, the rest is replaced with an ellipsis.

Comparison filters

These filters return true or false depending on the result of a comparison. They are typically useful for specifying the condition in an #{if} block.

Match

The Match filter searches the input for an occurrence of a given regular expression pattern. It returns true if an occurrence is found, and false otherwise. The regular expression should be provided in the .NET Framework format. Double quotes need to be used around any expressions that contain whitespace or special characters. Expressions containing double quotes can not be expressed inline, but can be done via nested variables.

StartsWith, EndsWith and Contains

The StartsWith, EndsWith and Contains filters compare the input to a given string argument. They return true if the argument matches, and false otherwise. The comparison is case-sensitive. Strings are compared as Ordinals. Double quotes need to be used around any expressions that contain whitespace or special characters. Expressions containing double quotes can not be expressed inline, but can be done via nested variables.

Conversion filters

These filters provide a mechanism to convert a value from one form to another.

Date filters

These filters are used to work with dates.

NowDate and NowDateUtc

The NowDate and NowDateUtc filters take no variable input but can take an additional optional right-hand-side argument the define the string format (Defaults to ISO-8601 Round-trip format).

Escaping filters

These filters apply format-specific escaping rules.

Extraction filters

These filters extract a part of value.

UriPart

The UriPart filter parses the input as a URI and extracts a specified part of it. A helpful error will be written to the output if there is an error in the input or the filter expression.

Differences from regular variable bindings

Because of the flexibility provided by the extended syntax, variables that are not defined will result in the source text, e.g. #{UndefinedVar} being echoed rather than an empty string, so that evaluation problems are easier to spot and debug. The if construct can be used to selectively bind to a variable only when it is defined, e.g. to obtain identical “empty” variable functionality as shown in the first example:

Server=#{if DatabaseServer}#{DatabaseServer}#{/if};

JSON parsing

Octostache 2.x includes an update to support parsing JSON formatted variables natively, and using their contained properties for variable substitution.

Given the variable:

And the template:

<h1>#{Custom.MyJson[Name]}</h1>
#{Custom.MyJson.Name} - #{Custom.MyJson.Description}
From: #{Custom.MyJson.Sizes[0].price | Format C}
Sizes: #{Custom.MyJson.Sizes}

The result will be:

<h1>t-shirt</h1>
t-shirt - Shirts are not shorts
From: $15.00
Sizes: [{size: "small", price: 15.00}, {size: "large", price: 20.00}]

There are a few things to note here:

• The Name property is extracted from the JSON using either dot-notation or indexing.
• Providing an explicit project variable overrides one obtained by walking through the JSON.
• Arrays can be accessed using standard numerical index notation.
• Variables can map to a sub-section of the JSON variable.

Repetition over json

Given the variables:

And the template:

Numbers:
#{each number in MyNumbers}
 - #{number}
#{/each}

Objects:
#{each item in MyObjects}
	#{item.Key}: #{item.Value.Price}
#{/each} 

The resulting text will be:

Numbers:
 - 5
 - 2
 - 4
 
Objects:
Cat: 11.5
Dog: 17.5

Learn more

• Variable blog posts

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Last updated Sunday, January 1, 2023