my %seen;
while (<>) {
  chomp;
  my @fields = split('\|', $_);
  if (my $record = $seen{$fields[0]}) {
    ... append @fields to $record...
  } else {
    $seen{$fields[0]} = ...some data structure...
  }
}
for my $k (keys %seen) {
  my $record = $seen{$k};
  # process $record
}