my $str = `who`;
[download]

To get a hash of it, you'd have to split the string on newlines, then split each line:

foreach my $line (split /\n/,$str) {
    my ($user, $remainder) = split /\s/,$_,2;
    $hash{$user}++;  # just increment the value
}
[download]

But you could also use open to read from who:

open(PIPE,"who |") or die "Can't run 'who': $!\n";
while(<PIPE>) {
    my ($user, $remainder) = split;  # implicit split splits $_ on /\s
++/
    $hash{$user}++;
[download]

Now you have a populated hash.

# sort by user
foreach my $user(sort keys %hash) {
    print "$user logged in $hash{$user} times.\n";
}
# sort by times users are logged in
foreach my $user(sort {$hash{$a} <=> $hash{$b}} keys %hash) {
    print "$user logged in $hash{$user} times.\n";
}
[download]

--shmem

_($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}