sub head($)
{
    my ($x, $xs) = split( ' ', ${$_[0]}, 2);
    ${$_[0]} = $xs;
    return $x;
}

##</code><code>##

my $msg = "new item x";
my $cmd = head \ $msg;
if ( $cmd eq 'new') {
   if ( head \ $msg eq 'item') {
      ...
   } 
} elsif ( $cmd eq 'set') {
   ...
}