Perl Arrays

A Perl array is a list variable that stores scalar values, and the variables can be of different types.

Array variables start with @. To access an array element, use the$ + variable name + [index value]format to read it, as in the following example:

Example

#!/usr/bin/perl @hits = (25, 30, 40); @names = ("google", "example", "taobao"); print "\$hits[0] = $hits[0]\n"; print "\$hits[1] = $hits[1]\n"; print "\$hits[2] = $hits[2]\n"; print "\$names[0] = $names[0]\n"; print "\$names[1] = $names[1]\n"; print "\$names[2] = $names[2]\n";

In the program, the $ symbol is escaped with \ so that it is output literally.

Executing the above program produces the following output:

$hits[0] = 25
$hits[1] = 30
$hits[2] = 40
$names[0] = google
$names[1] = example
$names[2] = taobao

Creating Arrays

Array variables start with the@symbol, with elements placed inside parentheses. You can also useqwto start defining an array.

@array = (1, 2, 'Hello');
@array = qw/这是 一个 数组/;

The second array uses theqw//operator, which returns a list of strings, with array elements separated by spaces. Of course, you can also use multiple lines to define an array:

@days = qw/google
taobao
...
example/;

You can also assign values to an array by index, as shown below:

$array[0] = 'Monday';
...
$array[6] = 'Sunday';

Accessing Array Elements

Access array elements using the$ + variable name + [index value]format to read, as in the following example:

Example

@sites = qw/google taobao example/; print "$sites[0]\n"; print "$sites[1]\n"; print "$sites[2]\n"; print "$sites[-1]\n"; # Negative numbers, read in reverse

Executing the above program produces the following output:

google
taobao
example
example

Array index values start from 0, i.e., 0 is the first element, 1 is the second element, and so on.

Negative numbers start reading from the reverse end, -1 is the first element, -2 is the second element.

Array Ranges

Perl provides an array form that can be output by sequence, with the formatstart value + .. + end value, as in the following example:

Example

#!/usr/bin/perl @var_10 = (1..10); @var_20 = (10..20); @var_abc = ('a'..'z'); print "@var_10\n"; # Print 1 to 10 print "@var_20\n"; # Print 10 to 20 print "@var_abc\n"; # Print a to z

Executing the above program produces the following output:

1 2 3 4 5 6 7 8 9 10
10 11 12 13 14 15 16 17 18 19 20
a b c d e f g h i j k l m n o p q r s t u v w x y z

Array Size

The size of an array is determined by the scalar context of the array:

Example

@array = (1,2,3); print "Array size:",scalar @array,"\n";

Executing the above program produces the following output:

数组大小: 3

The array length returns the physical size of the array, not the number of elements. We can look at the following example:

Example

#!/uer/bin/perl @array = (1,2,3); $array[50] = 4; $size = @array; $max_index = $#array; print "Array size:$size\n"; print "Maximum index:$max_index\n";

Executing the above program produces the following output:

数组大小:  51
最大索引: 50

From the output, we can see that the array has only four elements, but the array size is 51.

Adding and Removing Array Elements

Perl provides some useful functions to add and remove array elements.

If you have no programming experience before, you might ask what a function is. In fact, theprintwe used before is an output function.

The following table lists the common operation functions for arrays:

No.	Type and Description
1	push @ARRAY, LIST Places the list of values at the end of the array.
2	pop @ARRAY Deletes the last value of the array.
3	shift @ARRAY Pops the first value of the array and returns it. The array's index values are also decremented by one accordingly.
4	unshift @ARRAY, LIST Places the list at the front of the array and returns the number of elements in the new array.

Example

#!/usr/bin/perl # Create a simple array @sites = ("google","example","taobao"); $new_size = @sites ; print "1. \@sites = @sites\n"."Original array length:$new_size\n"; # Add an element at the end of the array $new_size = push(@sites, "baidu"); print "2. \@sites = @sites\n"."New array length:$new_size\n"; # Add an element at the beginning of the array $new_size = unshift(@sites, "weibo"); print "3. \@sites = @sites\n"."New array length:$new_size\n"; # Delete the element at the end of the array $new_byte = pop(@sites); print "4. \@sites = @sites\n"."Popped element:$new_byte\n"; # Remove the element at the beginning of the array $new_byte = shift(@sites); print "5. \@sites = @sites\n"."Popped element:$new_byte\n";

Executing the above program produces the following output:

Slicing Arrays

We can slice an array and return the new sliced array:

Example

#!/usr/bin/perl @sites = qw/google taobao example weibo qq facebook NetEase/; @sites2 = @sites[3,4,5]; print "@sites2\n";

Executing the above program produces the following output:

weibo qq facebook

Array indexing requires specifying valid index values, which can be positive or negative numbers. Each index value is separated by a comma.

If the indexes are consecutive, you can use..to specify a range:

Example

#!/usr/bin/perl @sites = qw/google taobao example weibo qq facebook NetEase/; @sites2 = @sites[3..5]; print "@sites2\n";

Executing the above program produces the following output:

weibo qq facebook

Replacing Array Elements

In Perl, array element replacement uses the splice() function, with the following syntax format:

splice @ARRAY, OFFSET [ , LENGTH [ , LIST ] ]

Parameter description:

@ARRAY: The array to be replaced.
OFFSET: The starting position.
LENGTH: The number of elements to replace.
LIST: The list of replacement elements.

The following example replaces 5 elements in the array starting from the 6th element:

Example

#!/usr/bin/perl @nums = (1..20); print "Before replacement - @nums\n"; splice(@nums, 5, 5, 21..25); print "After replacement - @nums\n";

Executing the above program produces the following output:

替换前 - 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
替换后 - 1 2 3 4 5 21 22 23 24 25 11 12 13 14 15 16 17 18 19 20

Converting a String to an Array

In Perl, converting a string to an array uses the split() function, with the following syntax format:

split [ PATTERN [ , EXPR [ , LIMIT ] ] ]

Parameter description:

PATTERN: Delimiter, defaults to a space.
EXPR: Specifies the string.
LIMIT: If this parameter is specified, it returns the number of elements in the array.

Example

#!/usr/bin/perl # Define a string $var_test = "example"; $var_string = "www-example-com"; $var_names = "google,taobao,example,weibo"; # Convert the string to an array @test = split('', $var_test); @string = split('-', $var_string); @names = split(',', $var_names); print "$test[3]\n"; # Print o print "$string[2]\n"; # Print com print "$names[3]\n"; # Print weibo

Executing the above program produces the following output:

o
com
weibo

Converting an Array to a String

In Perl, converting an array to a string uses the join() function, with the following syntax format:

join EXPR, LIST

Parameter description:

EXPR: Connector.
LIST: List or array.

Example

#!/usr/bin/perl # Define a string $var_string = "www-example-com"; $var_names = "google,taobao,example,weibo"; # Convert the string to an array @string = split('-', $var_string); @names = split(',', $var_names); # Convert the array to a string $string1 = join( '-', @string ); $string2 = join( ',', @names ); print "$string1\n"; print "$string2\n";

Executing the above program produces the following output:

www-example-com
google,taobao,example,weibo

Sorting Arrays

In Perl, sorting an array uses the sort() function, with the following syntax format:

sort [ SUBROUTINE ] LIST

Parameter description:

SUBROUTINE: Specifies the rule.
LIST: List or array.

Example

#!/usr/bin/perl # Define an array @sites = qw(google taobao example facebook); print "Before sorting: @sites\n"; # Sort the array @sites = sort(@sites); print "After sorting: @sites\n";

Executing the above program produces the following output:

排序前: google taobao example facebook
排序后: facebook google example taobao

Note: Array sorting is based on ASCII numeric values. Therefore, when sorting an array, it is best to first convert each element to lowercase before sorting.

Special Variable: $[

The special variable$[represents the first index value of an array. It is usually 0. If we set$[to 1, then the first index value of the array is 1, the second is 2, and so on. Here is an example:

Example

#!/usr/bin/perl # Define an array @sites = qw(google taobao example facebook); print "Website: @sites\n"; # Set the first index of the array to 1 $[ = 1; print "\@sites[1]: $sites[1]\n"; print "\@sites[2]: $sites[2]\n";

Executing the above program produces the following output:

网站: google taobao example facebook
@sites[1]: google
@sites[2]: taobao

In general, we do not recommend using the special variable$[. In new versions of Perl, this variable is deprecated.

Merging Arrays

Array elements are separated by commas. We can also use commas to merge arrays, as shown below:

Example

#!/usr/bin/perl @numbers = (1,3,(4,5,6)); print "numbers = @numbers\n";

Executing the above program produces the following output:

numbers = 1 3 4 5 6

You can also embed multiple arrays within an array and merge them into the main array:

Example

#!/usr/bin/perl @odd = (1,3,5); @even = (2, 4, 6); @numbers = (@odd, @even); print "numbers = @numbers\n";

Execute the above program, the output result is:

numbers = 1 3 5 2 4 6

Selecting Elements from a List

A list can be used as an array. Specifying an index value after the list can read the specified element, as shown below:

Example

#!/usr/bin/perl $var = (5,4,3,2,1)[4]; print "The value of var is =$var\n"

Execute the above program, the output result is:

var 的值为 = 1

Similarly, we can use in arrays..to read elements in the specified range:

Example

#!/usr/bin/perl @list = (5,4,3,2,1)[1..3]; print "The value of list = @list\n";

Execute the above program, the output result is:

list 的值 = 4 3 2

Other extensions