#! /usr/bin/perl -w

use strict;
use Data::Dumper;

my %hash;

while (<DATA>){
    # remove the newline
    chomp;
    # Split the data into an array
    my @data = split /,/,$_;
    # Match the filename and extension
    if ($data[2] =~ /(\w+)\.(\w+)/){
        
        # push
        push @{
            # onto an array refered to by the hash value
            $hash{lc $2}{$1}
        }, 
        # array values using a slice
        @data[3,4];
    }
}

print Dumper(\%hash);
__DATA__
abc,def,excel1.xls,12,some,time
hj,uyi,excel2.xls,12,more,time2
gh,ty,word1.doc,234,thing,time2
ksdj,hsjh,word2.doc,334,is,time3
[download]

$VAR1 = {
          'doc' => {
                     'word2' => [
                                  '334',
                                  'is'
                                ],
                     'word1' => [
                                  '234',
                                  'thing'
                                ]
                   },
          'xls' => {
                     'excel2' => [
                                   '12',
                                   'more'
                                 ],
                     'excel1' => [
                                   '12',
                                   'some'
                                 ]
                   }
        };
[download]