"  @{[...]}  " is an idiomatic pseudo-operator by combining several mechanisms

• String interpolation work not only for arrays but also for dereferencing of arrays.

  " @{$a_ref} "

• The [...] marks an anonymous array-ref.

  " @{[ 1, 2, 3 ]} "

• Lists can also include code statements to be executed

  " @{[ 1, 2, some_code() ]} "

• The returned list will be included into the string.

    DB<6> p ">>> @{[ 1, 2, time() ]} <<<"
  >>> 1 2 1680647910 <<<
    DB<7>
  [download]

update

added code examples for each step