[23:11][nick:~/monks]$ cat 1138950-2.pl
#!/usr/bin/perl -w

use strict;
use warnings;

my $x = 3;
my $y = 0;

for(1..3){
    $y = $x;
    $y++;
    $x -= $y;
}
[23:11][nick:~/monks]$ perl -d 1138950-2.pl

Loading DB routines from perl5db.pl version 1.49
Editor support available.

Enter h or 'h h' for help, or 'man perldebug' for more help.

main::(1138950-2.pl:6):	my $x = 3;
  DB<1> a 11 say $y                                                                                                            
  DB<2> n                                                                                                                      
main::(1138950-2.pl:7):	my $y = 0;
  DB<2>                                                                                                                        
main::(1138950-2.pl:9):	for(1..3){
  DB<2>                                                                                                                        
main::(1138950-2.pl:10):	    $y = $x;
  DB<2>                                                                                                                        
main::(1138950-2.pl:11):	    $y++;
3
  DB<2>                                                                                                                        
main::(1138950-2.pl:12):	    $x -= $y;
4
  DB<2>                                                                                                                        
main::(1138950-2.pl:10):	    $y = $x;
4
  DB<2>                                                                                                                        
main::(1138950-2.pl:11):	    $y++;
-1
  DB<2>                                                                                                                        
main::(1138950-2.pl:12):	    $x -= $y;
0
  DB<2>                                                                                                                        
main::(1138950-2.pl:10):	    $y = $x;
0
  DB<2>                                                                                                                        
main::(1138950-2.pl:11):	    $y++;
-1
  DB<2>                                                                                                                        
main::(1138950-2.pl:12):	    $x -= $y;
0
  DB<2>                                                                                                                        
Debugged program terminated.  Use q to quit or R to restart,
use o inhibit_exit to avoid stopping after program termination,
h q, h R or h o to get additional info.
Use of uninitialized value $y in say at (eval 18)[/Users/nick/perl5/perlbrew/perls/perl-5.22.0/lib/5.22.0/perl5db.pl:737] line 1.
 at (eval 18)[/Users/nick/perl5/perlbrew/perls/perl-5.22.0/lib/5.22.0/perl5db.pl:737] line 1.
	eval 'no strict; ($@, $!, $^E, $,, $/, $\\, $^W) = @DB::saved;package main; say $y;
' called at /Users/nick/perl5/perlbrew/perls/perl-5.22.0/lib/5.22.0/perl5db.pl line 737
	DB::eval called at /Users/nick/perl5/perlbrew/perls/perl-5.22.0/lib/5.22.0/perl5db.pl line 2681
	DB::DB called at /Users/nick/perl5/perlbrew/perls/perl-5.22.0/lib/5.22.0/perl5db.pl line 10345
	DB::fake::at_exit() called at /Users/nick/perl5/perlbrew/perls/perl-5.22.0/lib/5.22.0/perl5db.pl line 9916
	DB::END() called at (eval 18)[/Users/nick/perl5/perlbrew/perls/perl-5.22.0/lib/5.22.0/perl5db.pl:737] line 0
	eval {...} called at (eval 18)[/Users/nick/perl5/perlbrew/perls/perl-5.22.0/lib/5.22.0/perl5db.pl:737] line 0

  DB<2>