Okay, this is NOT production ready, or even sane for that matter, but I couldn't resist. I call it: "hashes2hashes.pl". The script creates a hash of key=>value pairs from the __DATA__. While it is adding to the hash, it creates an array of references to the data. It then uses the references as keys to another hash which stores the $key of the first hash as the data element. Now if you have a reference to a value in %hash1 you can use it to look up the corresponding key stored in %hash2. 

#!/usr/bin/perl

use Data::Dumper;

while(<DATA>){
chomp;
($key,$val)=split/=/;
#add key => value pair to %hash1
$hash1{$key}=$val;

#add reference to $hash1{$key} to @refs
push @refs,\$hash1{$key};

#create second %hash that stores the reference as a key and $key as th
+e value
$hash2{\$hash1{$key}}=$key;
}

#Now let's see how we can reference the various things.
print "Reference \$refs[0] is the value $refs[0] and points to: ${$ref
+s[0]}\n";
print "In \$hash2,  $refs[0] points to the value $hash2{$refs[0]}\n";
print "The key $hash2{$refs[0]} can be then used to reference \$hash1{
+\$hash2{\$refs[0]}} => $hash1{$hash2{$refs[0]}}\n";

# And some Dumper output to make sure it looks good.
print Dumper(\%hash1, \@refs, \%hash2);


__DATA__
key1=1
key2=2
key3=3




OUTPUT:

Reference $refs[0] is the value SCALAR(0x804c05c) and points to: 1
In $hash2,  SCALAR(0x804c05c) points to the value key1
The key key1 can be then used to reference $hash1{$hash2{$refs[0]}} =>
+ 1
$VAR1 = {
          'key2' => '2',
          'key1' => '1',
          'key3' => '3'
        };
$VAR2 = [
          \$VAR1->{'key1'},
          \$VAR1->{'key2'},
          \$VAR1->{'key3'}
        ];
$VAR3 = {
          'SCALAR(0x804c05c)' => 'key1',
          'SCALAR(0x804c194)' => 'key3',
          'SCALAR(0x804c140)' => 'key2'
        };

[download]

I remember reading that using references as hash keys was bad. Maybe someone who knows a little more perl internals can tell me if the references would ever change during my program(provided I don't copy %hash1 of course)? Or if there is some other horrid reason not to do things this way?

In reply to Re: Given ref to hash value, retrieve the key by pzbagel
in thread Given ref to hash value, retrieve the key by gazpacho

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