• Read perlintro.
• Write some code.
• When you encounter problems, post your code and ask specific questions.

Open the 2nd file (the 3000 number file). Read the first eight digits of each entry into a hash, where the eight-digit number is a hash key.

Open the 3000000 number file. For each entry in that file, take the first eight digits, and check for the existence of a matching hash key. If one exists, increment the value indexed by that key.

Sort the keys by their corresponding value.

Print the first 100 entries from the sorted list of hash keys.

Start with this:

#!/usr/bin/perl 
# ...or whatever shebang line your system requires

use strict;
use warnings;

# Follow the steps outlined above...
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perlintro will contain everything you need for this. It takes about a half hour to read through it. After having read perlintro, and after getting started, you will probably come up with more specific questions. When asked along with code to illustrate your sticking points, we'll be able to help you along.

Start with this:

#!/usr/bin/perl
use strict;
use warnings;
#psudo code from here on
# open the file with categories 
# read the categories in (probably to a hash where the key is the cate
+gory and the value 0)
# close the categories file (you have your hash, you don't need to rea
+d from the file anymore)
# open the file with 3000k entries
# read the file line by line
# for each line read
#    trim to the first 8 characters
#    look for that value in the hash keys
#    increment the value of the hash key that is matched if any
# you now have a hash with category as the key, and the number found a
+s the value
# you should be able to figure out how to find the top 100 values and 
+print out the key and value for each of them or store them to file
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Run the program using the -d (debugger) and learn to use that tool to examine and learn what those hashes and any other variables look like. It is a quick tool to learn to use if just doing basic examining for self-enlightenment.

PerlDoc is your friend. Tutorials like perldsc, perlop, perlfunc will all help you solve this pretty quickly, including example code much of the time.

Hope you find this helpful... Update:

Note that by using a hash, you eliminate the possibility of there being duplicate categories, simplifying and possibly making the effort more efficient.

Restated the increment step for clarity(I hope)

This is your task, first try yourself, if you struggle come here with the code you tried, we will help you better.

All good, it's working now after I've initialized the values :) the output is all the phone models in Uganda with the number of users having these phones. However, there are duplicates of models, with different values. Can you think of a way to add those values and have a unique model with all the values added up?

#!/usr/bin/perl


use strict;
use warnings;
use diagnostics;

open (IMEI, 'IMEI.txt');
open (TAC, 'tac.txt');
 my %mapToModel;
 my %keyCount;
 my $key;
 my $model;
 my $subs;
 my $keyCount;
 my $mapToModel;
 my $count;
 my %dictionary;

while (<TAC>){
         $key = substr $_,0,8;
         $model = substr $_,9;
         $keyCount{$key} = 0;
         $mapToModel{$key} = $model;
}


close (TAC);

while (<IMEI>){
          $subs = substr $_, 0, 8;
        if(exists $keyCount{$subs}){
                $keyCount{$subs} = $keyCount{$subs} +1;
        }
}
close (IMEI);
foreach my $key (keys %keyCount){
        if (exists $mapToModel{$key}){


                $model = $mapToModel{$key};
                $count = $keyCount{$key};

                foreach my$model (keys )


                if( $count !=0){

                 print "$count\t$model";

         }
        }






}
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#! /usr/bin/perl

use strict;
use warnings;

open (my $imeitag , '<', '/path/to/imei_tags.txt');
my %devices;
while(<$imeitag>){
  $devices{$1}=0 if /^\s*(\d{8}$/;
}

close $imeitag;

open (my $imei, '<', '/path/to/imeis.txt');
while(<$imei>){
  my $imeitag=$1 if /^\s*(\d{8}\d+\s*$/
  $devices{$imeitag}++ if defined $devices{$imeitag};
}

close $imei;

my $count=0;
for my $imeitag (sort {$devices{$a}<=>$devices{$b}} keys %devices){
  print "$imeitag\n";
  $count++;
  last if $count >=100;
}
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Some untested thoughts:

open (...);


Return status of open statements not checked; alternately,  use autodie; not used.

$devices{$1}=0 if /^\s*(\d{8}$/;


Capture group  (\d{8}$ not closed.

my $imeitag=$1 if /^\s*(\d{8}\d+\s*$/


Capture group  (\d{8}\d+\s*$ not closed; statement not terminated (missing semicolon);  my $imeitag ... if ... ; conditional creation of lexical (pre-state static variable hack).

for my $imeitag (sort {$devices{$a}<=>$devices{$b}} keys %devices){
    print "$imeitag\n";
    $count++;
    last if $count >=100;
}


Sorts keys of hash in ascending numerical order, but then prints first 100 keys, which does not seem in accord with requirement to "output ... the top 100 devices" (whatever "top" may exactly mean in the context of the OP).