Expressions

Substitution, field access, operators, function calls, pipes.

Inside {{ … }} you can put any expression. The result is converted to a string and emitted at that position in the output.

Substitution

The simplest expression is a field access. The . prefix references the current data context:

{{ .name }}
{{ .page.title }}
{{ .args[0] }}
{{ .map['some key'] }}

Bare identifiers (no leading .) reference local variables or template parameters.

Literals

{{ 'a string' }}      single-quoted
{{ "a string" }}      double-quoted (interchangeable)
{{ 42 }}              integer
{{ 3.14 }}            floating point
{{ true }}            boolean
{{ false }}
{{ null }}

Operators

{{ if .count > 10 and .show }}
  Many.
{{ end }}

Function calls

Any function in the renderer’s function map can be called directly. Most builtins are 1-arity and accept a pipe target.

{{ upper .name }}
{{ len .pages }}
{{ replace .text 'foo' 'bar' }}

Pipe syntax

The pipe operator | threads the previous value as the first argument to the next function. These two are equivalent:

{{ .name | upper | trim }}
{{ trim (upper .name) }}

Pipes read left-to-right, which is friendlier than nested calls when you have several transforms.

Method-style calls

Any 1-arity function can be invoked as a method on its receiver:

{{ .name.upper.trim }}
{{ .name | upper | trim }}
{{ trim (upper .name) }}

All three render the same output.

Grouping

Parentheses group expressions and force evaluation order:

{{ (1 + 2) * 3 }}
{{ if (.count > 0) and (.published) }}…{{ end }}

Conditional expression

The C-style ternary, written with then / else keywords for readability:

{{ if .draft then 'DRAFT' else 'LIVE' }}

(Different from the block-form {{ if … }} … {{ end }} — see Control flow.)

Truthiness

A value is truthy unless it’s:

• null
• false
• the empty string ""
• the empty list / map
• the integer 0 or float 0.0

if, and, or, and not all use this definition.