#!/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";
	}
}