$_ = ':Admin!Admin@leet-A0B340B0.host.com PRIVMSG #channel :!quit';
$channel = '#channel';

if($_ =~ /^:(.*)!(.*) PRIVMSG $channel :(.*)$/){
   my $user = $1;
   my $host = $2;
   my $message = $3;
   if ($message =~ /^!quit$/){
      die "Quiting!\n";
   }
}

__END__
output
======
Quiting!

##</code><code>##

if($_ =~ /^:([^!]*)!(\S*) PRIVMSG (#\S+) :(.*)$/){
   my $user = $1;
   my $host = $2;
   my $chnl = $3;
   my $message = $4;
   if ($chnl eq $channel) {
      if ($message =~ /^!quit$/){
         die "Quiting!\n";
      }
      ...
   }
}