The syntax works fine for me, $hash is just the hash of code referances $params->{action} is just the key for which one to call. Here is the surrounding code.

my $q =new CGI;
my $params=$q->Vars(); 

my %hash=('sub1'=>\&sub1,'sub2'=>\&sub2, ''=
>\&notfound);

main();
sub main {
    #call the sub as defined by cgi param 'action'
    &$hash{$params->{'action'}}->() ;
}
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Thanks all for the tip on pushing undef, don't know if I asked much of a question was just checking this is 'normal' behaviour Update My mistake somehow added quotes when retyping