# Read passwd files from @ARGV, outputting one record per
# username.  Duplicate usernames are renamed to be unique
my %users;
while (<>) {
  $user = split ":",$_,1;
#  next if exists $users{$user};
  $_ = "a$_" , redo if exists $users{$user};
  print;
  $users{$user} = 1;
}