An alternative to using a regex is substr applied at either end of the string.

johngg@aleatico:~$ perl -Mstrict -Mwarnings -E 'say q{};
my $char = q{0x388c818ca8b9251b393131c08a736a67ccb19297};
say join q{ ... },
   substr( $char, 0, 6 ),
   substr( $char, length( $char ) - 6, 6 );'

0x388c ... b19297
[download]

I hope this is helpful.

Update: Re. AnonyMonk's comment regarding negative offsets, I had completely forgotten that, how dumb am I :-(

Update 2: Here's the amended code.

johngg@aleatico:~$ perl -Mstrict -Mwarnings -E 'say q{};
my $char = q{0x388c818ca8b9251b393131c08a736a67ccb19297};
say join q{ ... },
   substr( $char, 0, 6 ),
   substr( $char, -6 );'

0x388c ... b19297
[download]