#!/usr/bin/perl

@old = ( 2, 5, 13, undef, 6, 8, undef, 3);

@new = ();

for ($i=0;$i<=$#old;$i++)
{
    $new[$n++] = $old[$i] if defined $old[$i];    }
    
print "\n@old";
print "\n\n@new\n\n";

 
$i=0;
foreach (@old)
{      if ($old[$i] != defined)
       {    splice @old,$old[$i],1; }
$i++;

}

#!/usr/bin/perl

use strict;
use warnings;

use Data::Dumper;

my @old = ( 2, 5, 13, undef, 6, 8, undef, 3);

# mit splice (rückwärts durch das Array)

for (reverse 0..$#old) {
    warn "splicing: \@old[$_]" and splice @old, $_, 1 unless defined $old[$_];
}

print Dumper \@old;

# ohne Zählvariable

@old = ( 2, 5, 13, undef, 6, 8, undef, 3);
my @new = ();

for (@old) { push @new, $_ if defined $_ };
@old = @new;

print Dumper \@old;

# die perl-typische Variante

@old = ( 2, 5, 13, undef, 6, 8, undef, 3);
@old = grep { defined } @old;
print Dumper \@old;

$new[$n++] = ...;

push @new, ...;