I would do it like this:

while (@vars)
{
        print "directive: ";

        print join " ", map munge_var($_),
                splice @vars, 0, 4;

        print $/;
}
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Update: if I were feeling crazy, I might instead do it like this:

sub print_directive
{
        return unless @_;

        print "directive: ";
        print join " ", map munge_var($_), splice @_, 0, 4;
        print $/;

        &print_directive;
}

print_directive @vars;
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