The math is simple if you have min and max from List::Util:

use strict;
use warnings;
use List::Util qw(min max);

my $range1 = "31-52";
my $range2 = "27-50";
print max(min($2,$4)-max($1,$3)+1,0),"\n" if "$range1,$range2"=~/(\d+)
+-(\d+),(\d+)-(\d+)/;
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Of course, each max or min could be replaced by the ternary operator ?:.