Range Operator in Perl

Perl Operators – Part 8

Perl Course

Foreword: In this part of the series, I talk about the Perl Range operator in list context. The range operator is a binary operator and it is ..

By: Chrysanthus Date Published: 12 Oct 2015

Introduction

This is part 8 of my series, Perl Operators. In this part of the series, I talk about the Perl Range operator in list context. The range operator is a binary operator and it is ".." without the quotes. You should have read the previous parts of the series before reaching here, as this is a continuation. The range operator is useful for writing foreach (1..10) loops and for doing slice operations on arrays. It can also be used for string ranges.

Array
Consider the following array:

    my @animals = ('dog', 'cat', 'cow', 'sheep', 'elephant', 'lion', 'tiger');

To return a copy of the values (list) in the array from index 1 to index 5, you can use:

    my $slice = @animals[1,2,3,4,5];

This slice is preferably written as in the following code using the range operator (try it):

use strict;

    my @animals = ('dog', 'cat', 'cow', 'sheep', 'elephant', 'lion', 'tiger');

    my @slice = @animals[1..5];

    print @slice;

foreach Loop
Remember that in Perl, “foreach” and “for” mean the same thing. The range operator can be used in the foreach loop as in the following code:

use strict;

foreach my $item (0..4)
        {
            print $item * 2; print "\\n";
        }

The output is:

0
2
4
6
8

The following code uses the range operator to print the position number and their corresponding values in an array.

use strict;

    my @arr = ('John', 'Peter', 'Mary');

     foreach (0..$#arr)
        {
            print "Number ", $_+1, " is ", $arr[$_], "\\n";
        }

The output is:

    Number 1 is John
    Number 2 is Peter
    Number 3 is Mary

Note that arrayName is found in the array definition statement and in the foreach list; that is why it is evaluated in the foreach loop. Remember that index counting for the array begins from zero and the last index for the array is $#arrayName.

Consider the following c-style for-loop:

use strict;

    my @arr = ('John', 'Peter', 'Mary');

     for (my $i=0; $i<@arr; ++$i)
        {
            print "Number ", $i+1, " is ", $arr[$i], "\\n";
        }

The following Perl-style for-loop operates faster than this one:

use strict;

    my @arr = ('John', 'Peter', 'Mary');

     foreach my $i (0..$#arr)
        {
            print "Number ", $i+1, " is ", $arr[$i], "\\n";
        }

The above three code samples do the same thing. The Perl-style samples, each operates faster than the c-style. So, you should always use the Perl-style foreach loop in Perl programs. The following is the recommended code for Perl to produce two-dimensional integers:

use strict;

    foreach my $i (0..2)
        {
            foreach my $j (0..3)
                {
                    print $i; print $j; print ", ";
                }
            print "\\n";
        }

The output is:

    00, 01, 02, 03
    10, 11, 12, 13
    20, 21, 22, 23

Strings
You can use the range operator to form a string range (and assign to an array). Read and try the following code that gives examples:

use strict;

    my @arr1 = "e".."n";
    print @arr1, "\\n";
    my @arrA = "E".."N";
    print @arrA, "\\n\\n";

    my @arr2 = "a".."z";
    print @arr2, "\\n";
    my @arrB = "A".."Z";
    print @arrB, "\\n\\n";

    my @arr3 = "3".."7";
    print @arr3, "\\n";
    my @arrB = "0".."9";
    print @arrB, "\\n\\n";

    my @mDays = ("01" .. "31");   #two digits days of the month
    print @mDays, "\\n\\n";

    my @hexDigits = (0 .. 9, "a" .. "f");   #two ranges for hexadecimal digits
    print @hexDigits, "\\n\\n";

The output is:

efghijklmn
EFGHIJKLMN

abcdefghijklmnopqrstuvwxyz
ABCDEFGHIJKLMNOPQRSTUVWXYZ

34567
0123456789

01020304050607080910111213141516171819202122232425262728293031

0123456789abcdef

The range operator is non-associative.

That is it for this part of the series. We stop here and continue in the next part.

Chrys

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