You can use a hash. I wrote some example code to show how you can use it.

my %Nicks; # global variable

# you accept the NICK, then
$Nicks{$client} = $nick;

# later on, when you get a message
$client->print("$Nicks{$client} $msg") # NICK message

# when the client disconnects
delete $Nicks{$client};
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