with

{{ $var := "foo" }}
{{ with $var }}
  {{ . }} → foo
{{ end }}

Use with the else statement:

{{ $var := "foo" }}
{{ with $var }}
  {{ . }} → foo
{{ else }}
  {{ print "var is falsy" }}
{{ end }}

Use else with to check multiple conditions:

{{ $v1 := 0 }}
{{ $v2 := 42 }}
{{ with $v1 }}
  {{ . }}
{{ else with $v2 }}
  {{ . }} → 42
{{ else }}
  {{ print "v1 and v2 are falsy" }}
{{ end }}

Initialize a variable, scoped to the current block:

{{ with $var := 42 }}
  {{ . }} → 42
  {{ $var }} → 42
{{ end }}
{{ $var }} → undefined

Understanding context

At the top of a page template, the context (the dot) is a Page object. Inside of the with block, the context is bound to the value passed to the with statement.

With this contrived example:

{{ with 42 }}
  {{ .Title }}
{{ end }}

Hugo will throw an error:

can't evaluate field Title in type int

The error occurs because we are trying to use the .Title method on an integer instead of a Page object. Inside of the with block, if we want to render the page title, we need to get the context passed into the template.

Use the $ to get the context passed into the template.

This template will render the page title as desired:

{{ with 42 }}
  {{ $.Title }}
{{ end }}

Gaining a thorough understanding of context is critical for anyone writing template code.