Perl Hash,associative arrays, lookup tables

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Assigning values to hash (or associative arrays/lookup tables)

hash tables consist of key/value pairs

every key is followed by a value values can be assigned to hash tables as

%us_states=
("California","Sacramento","Wisconsin","Madison","New York","Albany");

We can also use => operator to identify the key to the left, and the value to the right; if the => operator encounters bare words in key positions, they will be automatically quoted (note "New York", however, which consists of two words and MUST be quoted

%us_states=
(California=>"Sacramento",Wisconsin=>"Madison","New York"=>"Albany");

In above example California is key and Sacromento is value.
Similarily Wisconsin is key and Madison is value.

Printing:

print "Capital of California is " . $us_states{"California"} . "\n\n";

printing all values(using for loop):

#!/usr/bin/perl
%states=
(California=>"Sacramento",Wisconsin=>"Madison","New York"=>"Albany");
foreach my $keys(keys %us_states)
{
  print "KEY:$keys VALUE:$us_states{$keys}\n";
}
 
output
KEY:Wisconsin VALUE:Madison
KEY:New York VALUE:Albany
KEY:California VALUE:Sacramento

Note

Hashes have no internal order

Hashes of hashes

example...

%companies_products = (
        google => {
        email   => "gmail",
    },
    microsoft => {
        email   => "hotmail",
        database      => "MSsql server",
        "wordprocessing" => "ms office",  
    },
    yahoo => {
        email   => "yahoo mail",
        chat      => "yahoo messenger",
    },
);