Well assuming that $key = 'Varbind' and that $value is an array ref containing each part of the id, then you can use join:

print "$key: ".join('.',@$value)."\n";
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When you use an array in a string (like "@a"), perl translates this internally into join($", @a), one can see this if you turn perl's bytecode back into source code using B::Deparse.

--
integral, resident of freenode's #perl