Arrays

Introduction

Arrays let you store an ordered collection of values in a single variable, rather than creating a separate scalar for every item. If scalars are Perl's way of holding one thing, arrays are Perl's way of holding many things in a specific order — perfect for lists of usernames, file paths, log lines, or numbers.

What is an Array?

An array is an ordered, numbered list of scalar values. Array variable names always use the @ sigil, which signals "this variable holds multiple values" — the plural counterpart to the singular $ sigil used for scalars.

use strict;
use warnings;

my @fruits = ("apple", "banana", "cherry");
print "Fruits: @fruits\n";

Just like scalars, arrays are interpolated inside double-quoted strings — Perl automatically joins the elements with a single space between them by default.

Declaring and Accessing Arrays

Arrays are declared with my, just like scalars, followed by a parenthesized, comma-separated list of initial values.

use strict;
use warnings;

my @days = ("Monday", "Tuesday", "Wednesday", "Thursday", "Friday");
my @empty = ();   # an array can also start empty

print "Number of weekdays listed: ", scalar(@days), "\n";

scalar(@days) forces the array into scalar context, which returns its element count — we will look at this pattern more closely later in this lesson.

Indexing Elements

To access a single element of an array, switch the sigil to $ (because you are now asking for one scalar value) and provide the numeric index in square brackets. Perl array indexes start at 0, and negative indexes count backward from the end of the array.

use strict;
use warnings;

my @days = ("Monday", "Tuesday", "Wednesday", "Thursday", "Friday");

print "First day: $days[0]\n";
print "Third day: $days[2]\n";
print "Last day: $days[-1]\n";
print "Second-to-last day: $days[-2]\n";

Adding and Removing: push, pop, shift, unshift

Perl provides four core built-in functions for growing and shrinking an array from either end.

use strict;
use warnings;

my @queue = ("task1", "task2");

push(@queue, "task3");           # add to the end
unshift(@queue, "urgent-task");  # add to the beginning

print "Queue: @queue\n";

my $next_up = shift(@queue);     # remove from the beginning
print "Processing: $next_up\n";
print "Remaining queue: @queue\n";

my $last_task = pop(@queue);     # remove from the end
print "Removed from end: $last_task\n";
print "Final queue: @queue\n";

Array Length in Scalar Context

Perl arrays behave differently depending on whether they are used in list context or scalar context. When an array is evaluated in scalar context — for example, assigned to a scalar variable, or explicitly wrapped in scalar(...) — it evaluates to its element count, not its contents.

use strict;
use warnings;

my @colors = ("red", "green", "blue", "yellow");

my $count = @colors;          # scalar context: assigns the length, 4
my $last_index = $#colors;    # $#array gives the index of the last element

print "Number of colors: $count\n";
print "Last valid index: $last_index\n";

$#colors is a special notation that gives the index of the final element (always one less than the total count, since indexing starts at 0). This scalar-vs-list distinction is such a core Perl concept that an entire upcoming lesson, "Variables & Context," is dedicated to it.

Looping Over an Array

The foreach loop is the most natural way to process every element of an array in turn.

use strict;
use warnings;

my @scores = (88, 92, 79, 95);

foreach my $score (@scores) {
    print "Score: $score\n";
}

Common Mistakes

Best Practices

Frequently Asked Questions

Key Takeaways

Summary

Arrays give you ordered collections of data. Next, you will learn about hashes, which store data as key-value pairs rather than by numeric position, using the % sigil.