I'm going to go strictly off your description, as what you said you want to print out doesn't seem to match the description as I understand it.

I would just do something like this:

@ACCTS = ("1234", "5678", "6959");
open(IN,"InFile.txt");
%acct="";
while (defined($line = (<IN>))){
  foreach $x (@ACCTS) {
     if ($line =~/$x/){
       #only print the first line we see for each account
       unless( exists $acct{$x} ){
         print "$line\n";
         $acct{$x}++;
       }
     }
  }
}
[download]

Or if you need to store all the data for other purposes:

@ACCTS = ("1234", "5678", "6959");
open(IN,"InFile.txt");
%acct="";
while (defined($line = (<IN>))){
  foreach $x (@ACCTS) {
     if ($line =~/$x/){
       push(@{$acct{$x}},$line);
     }
  }
}

foreach $key (sort keys %acct){
   print "$key,$acct{$key}[0]\n";
}
[download]