In the vein of TMTOWTDI, I think this is clearer:

my $mac = "0:0A:0C:B:B8:F";
my @mac = split /:/, $mac;
$mac = join ':', map {sprintf '%02X', hex $_};
[download]

(BTW, this will reformat things that aren't even close to being valid MACs into things that look a little closer, but still aren't. For example, 'this::isn't:a:mac:foo' would become '00:00:0A:00:0F'.)

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