use strict;
use warnings;
use Data::Dumper;

my $n = 4;    # number of columns, given as user input
my %hcolumns; # this is the hash of the columns you are looking for

my @header = split /,/,<DATA>; # pls use Text::CSV for any real work
chomp @header;
while(<DATA>){
		chomp;
		my @record = split /,/;    # pls use Text::CSV for any real work
		for (0..$n-1) { 
				push @{ $hcolumns{$header[$_]} }, $record[$_]; 		}
}
print Dumper \%hcolumns; # hash of columns

__DATA__
Name,FirstName,Instrument
Mangelsdorff,Albert,Trombone
Parker,Charlie,Trumpet
Coltrane,John,Tenor
Evans,Bill,Piano