First, read the perl docs (try perldoc -f substr). You would use substr. In your case, the code would look like:

use strict;
use warnings;  # always a good idea

my $start = 12;
my $end   = 27;

my $string = 'a string at least 27 characters long with any random cha
+racters';

my $substring = substr($string, $start, ($end - $start));
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