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This subroutine is considered experimental, in order to use it you will need to do:

use experimental :pack;

multi sub pack(Str $template, *@items)
multi sub pack(@template, *@items)

Packs the given items according to the template and returns a buffer containing the packed bytes.

The template string consists of zero or more units that begin with an ASCII letter, and are optionally followed by a quantifier. For details, see unpack.