Use of uninitialized value but variables declared - perl

Question

use strict;
use warnings;
my $last_variable2= 'abc';
print "last var2 $last_variable2\n";
my #grouped;
while (<DATA>) {
my ($variable1,
$variable2,
$other_data) = split ',',$_,3;
if($variable2 ne 'abc'){
if( $variable2 ne $last_variable2){
print "\n\n";
print "'$variable2' doesn't equal '$last_variable2'\n";
my %HoA;
&process_data(#grouped_series);
#grouped = ();
}
}else{
print "Skipped this because it's the first\n";
}
push #grouped_series, $_;
$last_variable2 = $variable2;
}
When I run this code, I keep getting
Use of uninitialized value $last_variable2 in string ne at 1_1_correspondencer.pl line 32, <DATA> line 3.
Use of uninitialized value $variable2 in string ne at 1_1_correspondencer.pl line 33, <DATA> line 3.
Use of uninitialized value $last_variable2 in concatenation (.) or string at 1_1_correspondencer.pl line 36, <DATA> line 6.
But, I initialized both variables. Sorry, this is a naive question--I only just started using strict and warnings

Answer 1

When parsing your DATA, you don't verify that each of these variables is defined:
my ($variable1,
$variable2,
$other_data) = split ',',$_,3;
If there are no commas on a row, then $variable2 would be undefined which is later assigned to $last_variable2. Maybe add some data verification to take into account that case?
if (! defined $variable2) {
warn "missing variable2 definition: $_\n";
}
Without seeing your actual data, we can't really advise you more.