This seems to work:

#!/bin/perl -w
use strict;

my @array = ([1,2,3],[5,5,6],[1,4,6]);

# nb => number of arrays in which the number is found
my %in_array;

foreach my $array (@array)
  { # the keys of %unique_for_array are the (unique) numbers in the ar
+ray
    my %unique_for_array= map { $_, 1} @$array;
    # now use those unique numbers to count
    $in_array{$_}++ foreach keys %unique_for_array;
  }

# get the duplicates
my @duplicates= grep { $in_array{$_} > 1 } keys %in_array;
print "duplicates: ", join( ', ',  @duplicates), "\n";
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