default

Used to set a default value for a variable. If the variable is unset or an empty string, the given default value is printed instead. Default takes the one argument.

Parameter Position	Type	Required	Default	Description
1	string	No	empty	This is the default value to output if the variable is empty.

Template:

{$articleTitle = 'Dealers Will Hear Car Talk at Noon.'}
{$email= ''}

{$articleTitle|default:'no title'}
{$myTitle|default:'no title'}
{$email|default:'No email address available'}

output:

Dealers Will Hear Car Talk at Noon.
no title
No email address available

see also default in PHP Smarty documentation.