Joost and others have already pointed out the mistake you made with references.

However, I'd also like to point out that it would help if you simplified your code. Instead of keeping separate structures for count and the list of ttys, why not just keep those in a single hash of arrays structure.

Also, please note that you should limit the scope of your variables to their smallest possible scope. This gives "use strict;" the best chance of helping with syntax errors and also is the most obvious way to self-document your code. 
#!/usr/bin/perl -w

use strict;

my %ttys_of;

foreach (`who`) {
    my ($user, $tty) = /(\S+)\s+(\S+)/;
    push @{$ttys_of{$user}}, $tty;
}

foreach my $user (sort keys %ttys_of) {
    my $ttys = $ttys_of{$user};
    
    if (@$ttys == 1) {
        print "user $user is ONLY logged in at one place $ttys->[0]\n"
+;
    } else {
        print "user $user is logged in at: " . join(' ', sort @$ttys) 
+. "\n";
    }
}

[download]
- Miller

Update 4:20 UTC: Fixed this line my $ttys = @{$ttys_of{$user}};

In reply to Re: reference question by wind
in thread reference question by convenientstore

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