Conditional Syntax

Conditional syntax similar to that used in Unix shells may also be used:

%{​%{Foo}:-bar}

This code returns the value of %{Foo}, if it has a value. Otherwise, it returns a literal string bar.

%{​%{Foo}:-%{Bar}}

This code returns the value of %{Foo}, if it has a value. Otherwise, it returns the expansion of %{Bar}.

These conditional expansions can be nested to almost any depth, such as with %{​%{One}:-%{​%{Two}:-%{Three}}}.