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

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

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

next unless $meat;

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

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

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

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

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