Given that backticks in list context return a list of lines, and each line starts with the username (which you want to use as a key), I'd do something like:

my %who;
foreach my $user (`who`) {
    $user =~ /^(\S+)/ or next;
    $who{$1}++;
}
while (my($user, $count) = each(%who)) {
    print "$user is logged in $count time";
    print $count == 1 ? ".\n" : "s.\n";
}
[download]

who -q just gives the total number of users logged in on my system, so that's not very useful for counting how often each user is logged in.

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