From type/Proc

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method spawn(*@args ($, *@), :$cwd = $*CWD, Hash() :$env = %*ENV, :$arg0,
             :$win-verbatim-args = False --> Bool:D)

Runs the Proc object with the given command, argument list, working directory, and environment.

If :arg0 is set to a value, that value is passed as arg0 to the process instead of the program name.

On Windows the flag $win-verbatim-args disables all automatic quoting of process arguments. See this blog for more information on windows command quoting. The flag is ignored on all other platforms. The flag was introduced in Rakudo version 2020.06 and is not present in older releases.