use strict;
use warnings;
use String::Util 'trim'; 
use List::MoreUtils qw(uniq);

open IN, "<$ARGV[0]"
    or die "Could not open input file '$ARGV[0]' $!";

my $row;
my $val;
my $counter = 0;
my @trnAccounts;
my @unique_accounts;

while ($row = <IN>)
{
    $val = substr($row,0,1);
    @trnAccounts = substr($row,1050,50);
    @trnAccounts = trim (@trnAccounts);
    @unique_accounts = uniq (@trnAccounts);

    foreach (@unique_accounts) {
        $counter++;
        print $counter, ":";
        print @unique_accounts, "\n";
        #print $_, "\n"; this also prints all values
    }
}