To read data from a file given as a command line argument (e.g. ./script.pl data.txt):

#!/usr/bin/perl
use strict;
use warnings;

# Read data from file
my $file = shift @ARGV;
die "Usage: $0 <data-file>\n" unless $file;
open FH, "<", $file or die "Can't open '$file': $!\n";

# Cristoforo's code (same as above)
my %data;
while (<FH>) {
    chomp;
    my ($v, $k) = split /,/;
    $data{ $k } += $v;
}

close FH;

print "$data{$_},$_\n" for sort keys %data;
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Have a nice day, j