tie my @nums, 'Tie::File', $filename;

##</code><code>##

min(@nums);
max(@nums);

##</code><code>##

$ cat pm_num_list.txt
123
12e3
12e-3
-12e3
-123

##</code><code>##

#!/usr/bin/env perl

use strict;
use warnings;
use autodie;

use List::Util qw{min max};
use Tie::File;

tie my @nums, 'Tie::File', 'pm_num_list.txt';

print 'Min: ', min(@nums), "\n";
print 'Max: ', max(@nums), "\n";

untie @nums;

##</code><code>##

Min: -12e3
Max: 12e3