You've (accidentally) stumbled upon a new (5.6) feature. Quoting perldoc perldata: ... a literal of the form v1.20.300.4000 is parsed as a string composed of characters with the specified ordinals.

print ".102.111.111 - ", .102.111.111; #prints ".102.111.111 - foo?
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This actually parses as:

print ".102.111.111 - ", v0.102.111.111;
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Since it's a numeric literal with multiple `.'s, it's interpreted as a v-string (there's actually a hidden \0 there as the first character). In your second example, you don't have a literal with more than two dots, so it parses as print ".$num.111.111 - ",. $num . 111.111.