The problem is you're actually declaring your array variable as "@1" (that's a "one"). Variable names can't start with a numeral. Here's your script, cleaned up a bit (remember to use warnings and stricture, use "or" where you can instead of "||", and you might want to try lexical (scalar) filehandles). This version actually compiles, but I don't know what you want it to do

#!/usr/bin/perl

use warnings;
use strict;
use Data::Dumper;
use PDL;
use PDL::Matrix;

my $file = $ARGV[0];

#open(DATA, "<", $file)
        #or die "Error: Unable to open $file:$!\n";

my $d = [[],[], [], []];

while ( <DATA> )
{
  chomp;

  my @l = split(/,/);

  push @{$d->[0]}, $l[0];
  push @{$d->[1]}, $l[1];
  push @{$d->[2]}, $l[2];
  push @{$d->[3]}, $l[3];
}

$d = PDL::Matrix->pdl($d);

__DATA__
-0.821,-0.247,0.001,-0.77
-1.045,-0.289,0.035,-0.962
-1.345,-0.345,0.048,-1.188
-1.674,-0.421,0.041,-1.428
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