Using max and min from List::Util.

#!/usr/bin/perl
use strict;
use warnings;
use List::Util qw/ min max /;

my $hash = overlap('31-52', '27-50');
use Data::Dumper; print Dumper $hash;

sub overlap {
    my ($r1_lo, $r1_hi, $r2_lo, $r2_hi) = map {split /-/} @_;
    my $min = max($r1_lo, $r2_lo);
    my $max = min($r1_hi, $r2_hi);
    
    return if $min > $max;
    return {min => $min, max => $max};
}
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Prints:

$VAR1 = {
          'min' => 31,
          'max' => 50
        };
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