Answer

In Perl, variables are divided into scalars ($), arrays (@), and hashes (%):

• Scalars ($variable) – store a single value (string, number):

  my $name = "Ivan";
  my $age = 30;

• Arrays (@array) – a set of ordered elements (indexed by numbers):

  my @fruits = ("apple", "banana", "cherry");
  print $fruits[1]; # banana

• Hashes (%hash) – a set of key-value pairs (associative array):

  my %colors = (red => "#ff0000", green => "#00ff00");
  print $colors{"red"}; # #ff0000

Note that accessing an element uses a specific symbol depending on the type of variable:

• $array[0] — element of the array
• $hash{"key"} — value of the hash by key

Trick Question

What is the difference between the expressions @array[1,2] and $array[1,2]?

Answer:

• @array[1,2] — provides a list of multiple elements from the array (slice).
• $array[1,2] — incorrect, leads to an error. To access multiple elements of an array, only the slice @array[...] should be used.

Example:

my @array = (10, 20, 30, 40);
my @slice = @array[1,2]; # (20, 30)

Examples of real errors due to not knowing the subtleties of the topic

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Story

In a logging project, a programmer accessed a hash element using @colors{"red"}. As a result, it produced not the value of the hash, but a random error because a $ is needed for a single value, not @.

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Story

In one service, while iterating over the indexes of an array, the correct access was forgotten — instead of $array[$i], @array$i was used, leading to warnings and incorrect results.

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Story

In an API project, a function was described to take an array as $args, but an array was passed on the call without the scalar: func(@list). It turned out that this way the elements of the array are "unfolded" into a list, and the function did not work as expected. It was correct to accept the array as @args.