Checking existence in hash of hashes without adding entries

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

Hi,

I'm coding some logging configuration info into hash of hashes - for instance:

my %Log_names = (
               "BM_therm_boiler_00_state"  => { 'events_log' => 1 },
               "BM_therm_house_00_state"  => { 'events_log' => 1 },
               "BM_therm_hpump_00_state"  => { 'events_log' => 1 },
               "BM_swi_"  => { 'device_log' => 1 },
              );
[download]

Now I'd like to check for certain key whether it exists and retrieve it's content. But using simple exists or defined with double hashes, like

if exists $Log_names{"BM_light_test_00_"}{"device_log"}
[download]

I get the right result but it seems that keys are added to hash. Can I prevent this ?

$VAR1 = {
          'BM_light_test_00_' => {},
          'BM_swi_' => {
                         'device_log' => 1
                       },
          'BM_therm_house_00_state' => {
                                         'events_log' => 1
                                       },
          'BM_therm_boiler_00_state' => {
                                          'events_log' => 1
                                        },
          'BM_therm_hpump_00_state' => {
                                         'events_log' => 1
                                       }
        };
[download]

How to properly check existence and retrieve its content from hash of hashes ?

Thanks in advance,

regards,

Rob.

Comment on Checking existence in hash of hashes without adding entries Select or Download Code

Replies are listed 'Best First'.
Re: Checking existence in hash of hashes without adding entries by ccn (Vicar) on Dec 19, 2008 at 21:20 UTC
`if exists $Log_names{"BM_light_test_00_"} and exists $Log_names{"BM_light_test_00_"}{"device_log"}` [download]	[reply] [d/l]
Re: Checking existence in hash of hashes without adding entries by holli (Abbot) on Dec 19, 2008 at 22:13 UTC
You've been bitten by autovivification. holli, /regexed monk/	[reply]
Re: Checking existence in hash of hashes without adding entries by Your Mother (Archbishop) on Dec 19, 2008 at 22:29 UTC
Give Data::Diver a look.	[reply]
Re: Checking existence in hash of hashes without adding entries by lakshmananindia (Chaplain) on Dec 20, 2008 at 03:23 UTC
Here is the another way using ref `if(ref $Log_names{BM_light_test_00_} eq 'HASH' && exists($Log_names{BM +_light_test_00_}{device_log})) { print "Exists\n"; }` [download]	[reply] [d/l]