my @beef = @{ $dataset->{ $col[0] } };

##</code><code>##

my $key  = $col[0] ;
my $meat = $dataset->{ $key };
my @beef = @{ $meat };

##</code><code>##

## no warnings or errors
$ perl -e "print @{ undef() }; print 6"
6

## a warning is issued, but 6 still gets printed
$ perl -we "print @{ undef() }
Use of uninitialized value in array dereference at -e line 1.
6

## with strict the warning is fatal, 6 not printed cause program died
$ perl -Mstrict -we "print @{ undef() }
Can't use an undefined value as an ARRAY reference at -e line 1.

##</code><code>##

next unless $meat;

##</code><code>##

push @{$data[$nr - 1]->{shift(@cols)}},\@cols;

##</code><code>##

push @{ $data[ $nr - 1 ]->{ shift(@cols) } }, \@cols;

##</code><code>##

push @{
    $data[ $fileCount ]->{
        shift @col
    }
},  \@col;

##</code><code>##

my $Hashref = $data[ $fileCount ];
if( not $Hashref){
    $Hashref = $data[ $fileCount ] = {};
}
my $key = shift @col;
my $Arrayref = $Hashref->{ $key };
if( not $Arrayref ){
    $Arrayref = $Hashref->{ $key } = [];
}
push @{ $Arrayref },  \@col;

##</code><code>##

my $Hashref = $data[ $fileCount ];
if( not $Hashref){
    my %newHashThatIsOnlyNamedHere;
    $Hashref = $data[ $fileCount ] = \%newHashThatIsOnlyNamedHere;
}
my $key = shift @col;
my $Arrayref = $Hashref->{ $key };
if( not $Arrayref ){
    my @newArrayThatIsOnlyNamedHere;
    $Arrayref = $Hashref->{ $key } = \@newArrayThatIsOnlyNamedHere;
}
push @{ $Arrayref },  \@col;