#!/usr/bin/perl -w
#Tilte: final_problem7.pl
use strict;

if ( @ARGV eq 0 ){  die "Usage:\t$0\tdata_file\n"; }  
my $data_file = shift ;

# open data.
open (DATA,"<$data_file") or die "Could not open $data_file: $!\n";

my %phonebook;

#Split the data into hash of arrays
while (<DATA>){
  chomp( my ($name, $number) = split (/:/, $_));
  #Perl cookbook recipie 276-277: Hash of Arrays
  push @{ $phonebook{$number}},"$name" ;
}

#print the results
for my $phone (keys %phonebook){
  
  print "$phone:",join(", ", @{ $phonebook{$phone}}),"\n";
}