Perl List

Summary: in this tutorial, you’ll learn about the Perl list and how to manipulate list elements using various techniques such as list slicing, ranging and qw() function.

Introduction to Perl List

A Perl list is a sequence of scalar values. You use parenthesis and comma operators to construct a list. Each value is the list is called list element. List elements are indexed and ordered. You can refer to each element by its position.

Simple Perl list

The following example defines some simple lists:

();
(10,20,30);
("this", "is", "a","list");Code language: Perl (perl)

In the example above:

• The first list () is an empty list.
• The second list (10,20,30) is a list of integers.
• The third list ("this", "is", "a","list") is a list of strings.

Each element in the list is separated by a comma (,). In the previous tutorials, we used the print operator many times to display a number or a string. The print operator is a list operator. So let’s display our lists above with the print operator to see how it works:

#!/usr/bin/perl
use warnings;
use strict;

print(()); # display nothing
print("\n");
print(10,20,30); # display 102030
print("\n");
print("this", "is", "a","list"); # display: thisisalist
print("\n");Code language: Perl (perl)

We passed several lists to the print operator to display their elements. All the lists that we have seen so far contain an element with the same data type. These lists are called simple lists.

Complex Perl list

A Perl list may contain elements that have different data types. This kind of list is called a complex list. Let’s take a look at the following example:

#!/usr/bin/perl
use warnings;
use strict;

my $x = 10;
my $s = "a string";
print("complex list", $x , $s ,"\n");Code language: Perl (perl)

Using qw function

Perl provides the qw() function that allows you to get a list by extracting words out of a string using the space as a delimiter. The qw stands for quote word. The two lists below are the same:

#!/usr/bin/perl
use warnings;
use strict;

print('red','green','blue'); # redgreenblue
print("\n");

print(qw(red green blue)); # redgreenblue
print("\n");Code language: Perl (perl)

Similar to the q/ and q// operators, you can use any non-alphanumeric character as a delimiter. The following lists are the same:

qw\this is a list\;
qw{this is a list};
qw[this is a list];Code language: Perl (perl)

Flattening list

If you put a list, called an internal list, inside another list, Perl automatically flattens the internal list. The following lists are the same:

(2,3,4,(5,6))
(2,3,4,5,6)
((2,3,4),5,6)Code language: Perl (perl)

Accessing list element

You can access elements of a list by using the zero-based index. To access the n^th element, you put (n – 1) index inside square brackets.

Let’s take a look at the following example:

#!/usr/bin/perl
use warnings;
use strict;

print(
     (1,2,3)[0] # 1 first element
);
print "\n"; # new line

print(
     (1,2,3)[2] # 3 third element
);
print "\n"; # new lineCode language: Perl (perl)

To get multiple elements of a list at a time, you can put a list inside square brackets. This feature is called list slice. You can omit the parenthesis of the list inside the square bracket.

(1,2,3,4,5)[0,2,3] # (1,3,4)Code language: Perl (perl)

The above code returns a list of three elements (1, 3, 4).

Ranges

Perl allows you to build a list based on a range of numbers or characters e.g., a list of numbers from 1 to 100, a list of characters from a to z. The following example defines two lists:

(1..100)
(a..z)Code language: Perl (perl)