How to create and use a hash in Perl

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A hash, or more technically an associative array, assigns a key to a value. For example, let's say you have the following key:value pairs.

Key Value
Name Jeremy Canfield
ID 123456
Occupation Engineer

 

In this example, a variable named %hash is created, and the %hash variable contains the key:value pairs.

my %hash = ('name' => Jeremy, 'id' => 123456, 'occupation' => Engineer);

 

You can then print the value of a hash item. For example, the following will print the value of the name key, which is "Jeremy".

print $hash{name};

 


Start with an empty hash

Some Perl scripts will begin by creating a hash that does not contain any key:value pairs.

my %hash = ();

 

Then, somewhere in the script key:value pairs will be created. In this example, a key called "name" is created with a value of "Jeremy" and another key called "occupation" with a value of "engineer".

$hash{name}       = ("Jeremy");
$hash{occupation} = ("Engineer");

 

You can then print the values associated with a hash key.

print $hash{name};
print $hash{id};
print $hash{occupation};

 


Variables

You can create a variable for one or more of the key:value pairs.

$username = $hash{name};
$userid = $hash{id};
$useroccupation = $hash{occupation};

 

You can then print the value's associated with each key:value pair.

print $username;
print $userid;
print $useroccupation;

 


Loop through keys

You will usually want to loop through the hash. The following foreach loop will print the keys.

foreach $keys (keys %hash) {
    print $keys;
}

 

The following foreach loop will print the value associated with each key.

foreach $keys (keys %hash) {
    print $hash{$keys};
}

 


Loop through values

The following foreach loop with print the values.

foreach $values (values %hash) {
    print $values;
}

 

This will print the values.

Jeremy Canfield
123456
Engineer

 



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