#! /usr/bin/perl
open(PW,"ypcat passwd|") || die "How did you get logged in?";
while (<PW>) {
    chomp;
    ($user, $gcos) = (split /:/)[0,4];
    ($real) = split /,/, $gcos;
    ($first) = split /\s+/, $real;
    $names{$first} .= " $user;";
}
foreach (keys %names) {
    $this = $names{$_};
    if ($this =~ /; /) {
        print "$_ is used by:$this\n";
    }
}