See autovivification, a pragma (available from CPAN) that can lexically disable autovivification (the behavior). Here's an example from perlfaq4:

{
    no autovivification;
    my %hash;
    if( exists $hash{key1}{key2}{key3} ) {
        ...;
    }
}
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The faq also suggests a few other techniques.

thanks for the suggestion. but i'm planning to write my own function to check if a hash key exists without autovivification :-)

You should be testing using exists, because the boolean test you are using will return false if the hash element exists but is undef or zero or the empty string...

That said, I don’t think there is any way to do what you want without the clumsy cascade of tests:

if (exists $Hash{'2013'} && exists $Hash{'2013'}{'Oct'} && ...
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because exists also autovivifies intervening elements. According to the documentation:

This surprising autovivification in what does not at first—or even second—glance appear to be an lvalue context may be fixed in a future release.

:-(

Noted and thanks for your prompt response.

> I only want to be here if I set $Hash{'2013'}{'Oct'}{'11th'} = 1 explicitly.

If you only check  if ($Hash{'2013'}{'Oct'}{'11th'} == 1) { .. } you can't be bothered by hash-refs.

Anyway better rethink your concept!

When setting $Hash{'2013'}{'Oct'}{'11th'} = 1 you are overwriting a potential hashref to a nested hash and any previous $Hash{'2013'}{'Oct'}{'11th'}{'1AM'}{'30Min'}=1 will be lost.

Better use an additional level of keys to mark and write and test $Hash{'2013'}{'Oct'}{'11th'}{MARK} or so.

sorry for the confusion. the examaple i gave wasn't perfect. what i wanted to say is

  ## I only want to be here if I set
  ## $Hash{'2013'}{'Oct'}{'11th'} 
  ## or $Hash{'2013'}{'Oct'}{'11th'}{...}...{...}
  ## explicitly.
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Then the only practical solution is to switch off autovivification. But take care to do it only in a limited scope because many other modules may still need it and could break unexpectedly if it is switched off.;

It is probably more safe to do a no autovivification 'exists'; as this turns off autovivification for dereferencing expressions that are parts of an exists only, such as :

exists $arrayref->[1][2][$idx]
exists $hashref->{this}{that}{$key};
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and then make sure you change your tests to include the exists function.

CountZero

A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James

My blog: Imperial Deltronics

Data::Diver it dives the hash without autovivification

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