Hashes in Perl

Hashes are group of key-value pairs. Hash variables are prefixed with “%” sign. Lets take a simple example first then we will discuss the hash in detail.

#!/usr/bin/perl

%age = ('Chaitanya Singh', 29, 'Ajeet', 28, 'Lisa', 25);

print "\$age{'Lisa'}: $age{'Lisa'}\n";
print "\$age{'Chaitanya Singh'}: $age{'Chaitanya Singh'}\n";
print "\$age{'Ajeet'}: $age{'Ajeet'}\n";

Output:

$age{'Lisa'}: 25
$age{'Chaitanya Singh'}: 29
$age{'Ajeet'}: 28

In the above example, we have created a hash and displayed its elements. Lets see each part in detail:

Creating a hash

First method: This is what we have seen in the example above –

%age = ('Chaitanya Singh', 29, 'Ajeet', 28, 'Lisa', 25);

Here ‘Chaitanya Singh’ is the key 1 and 29 is value 1
‘Ajeet’ is key 2 and 28 is value 2
similarly ‘Lisa’ and 25 is third key-value pair.

Second method: This is the preferred way of creating a hash as it improves the readability. In this method we seperate key and value of each pair with ‘=>’ symbol.
For example:

%age = ('Chaitanya Singh' => 29, 'Ajeet' => 28, 'Lisa' => 25);

Useful Hash functions:

1) keys function:
keys function returns the list of all the keys in a hash.
Example:

#!/usr/bin/perl

%age = ('Chaitanya Singh' => 29, 'Ajeet' => 28, 'Lisa' => 25);
my @k = keys %age;
print "Keys: @k\n";

Output:

Keys: Ajeet Chaitanya Singh Lisa

2) values function:
values function returns the list of all the values in a hash.
Example:

#!/usr/bin/perl

%age = ('Chaitanya Singh' => 29, 'Ajeet' => 28, 'Lisa' => 25);
my @k = values %age;
print "Values: @k\n";

Output:

Values: 28 29 25

3) each function:
each function is used for iterating over a hash, it is generally used in while loop.
Example:

#!/usr/bin/perl

%age = ('Chaitanya Singh' => 29, 'Ajeet' => 28, 'Lisa' => 25);
while ( ($key, $value) = each %age ) { 
      print "Key: $key, Value: $value\n";
}

Output:

Key: Lisa, Value: 25
Key: Chaitanya Singh, Value: 29
Key: Ajeet, Value: 28