How to use foreach loop to iterate over arrays in Perl?

In Perl, the foreach loop (also aliased as for) is the most common and convenient way to iterate over elements of an array. It lets you process each element one by one without manually managing indexes. This makes your code clearer, shorter, and less error-prone.

Basic syntax of foreach

The syntax looks like this:

foreach my $element (@array) {
    # do something with $element
}

Here, @array is the array you want to loop over, and $element is a scalar variable that takes on the value of each element in turn. Inside the loop block, you can use $element just like any other scalar.

Key concepts in Perl foreach loops

• Sigils: Notice how @array has the "array" sigil @. When used in foreach, it expands to the list of elements. The loop variable is scalar ($element) because each item is one scalar at a time.
• Aliases: The loop variable ($element) is an alias to the actual array element. Modifying $element inside the loop changes the original array value.
• TMTOWTDI: Perl is flexible; you can use either foreach or just for as a loop keyword—they work the same for list iteration.
• Context: The loop iterates in list context over the array, so all elements are visited in order.

Example: Iterating over an array and printing each element

use strict;
use warnings;

my @languages = ('Perl', 'Python', 'Ruby', 'JavaScript');

foreach my $lang (@languages) {
    print "I like $lang\n";
}

Running this will output:

I like Perl
I like Python
I like Ruby
I like JavaScript

Modifying elements in a foreach loop

Because the loop variable aliases the original element, you can modify the array in-place:

foreach my $lang (@languages) {
    $lang = uc($lang);  # convert to uppercase
}
print join(", ", @languages), "\n";  # prints: PERL, PYTHON, RUBY, JAVASCRIPT

Common pitfalls

• Using a foreach loop variable without my can cause issues with variable scope, especially in strict mode.
• Modifying the array size inside the loop is not recommended—it may lead to unexpected behavior.
• If you want to iterate by index instead, you can use a C-style for loop with indexes, but foreach is preferred for direct element access.

Summary

The foreach loop is an easy and expressive way to iterate over arrays in Perl. Remember the signature:

foreach my $element (@array) {
    # use $element here
}

This loop variable aliases the current element, and you can read or modify it. Whether you're printing elements, transforming them, or processing data, foreach offers a clean syntax aligned with Perl’s flexible philosophy.