#!/usr/bin/perl

use strict;
use warnings;

my $x = 5;
$x = $x + ++$x + $x++;
print "x: $x\n";

my $y = 5; # avoid any contamination from first group.
$y = ++$y + $y++ + $y;
print "y: $y\n";

exit;

__END__

Output:

[~/perl/test]# ./prepost.pl 
x: 18
y: 20