Perl array

Array A is an unordered list variable that stores scalar values.

Array variables start with @. To access array elements, use the $ + variable name + [index value] format to read. The example is as follows:

#!/usr/bin/perl

@hits = (25, 30, 40);             
@names = ("google", "php", "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";

The $ symbol in the program is escaped with \, allowing it to be output as is.

Execute the above program, the output result is:

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

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Create array

The array variable starts with the @ symbol, and the elements are placed in brackets , you can also define an array starting with qw.

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

The second array uses the qw// 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
...
php/;

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

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

---

Accessing array elements

To access array elements, use the $ + variable name + [index value] format to read. The example is as follows:

@sites = qw/google taobao php/;

print "$sites[0]\n";
print "$sites[1]\n";
print "$sites[2]\n";
print "$sites[-1]\n";    # 负数，反向读取

Execute the above program, and the output result is:

google
taobao
php
php

array Index values ​​start at 0, which is 0 for the first element, 1 for the second element, and so on.

Negative numbers are read from the reverse direction, -1 is the first element, -2 is the second element

---

Array sequence number

Perl provides Array form that can be output in sequence, the format is start value + .. + end value, the example is as follows:

#!/usr/bin/perl

@var_10 = (1..10);
@var_20 = (10..20);
@var_abc = (a..z);

print "@var_10\n";   # 输出 1 到 10
print "@var_20\n";   # 输出 10 到 20
print "@var_abc\n";  # 输出 a 到 z

<p>执行以上程序，输出结果为：</p>
<pre>
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 array size is given by Determined by the context of the scalar in the array. :

@array = (1,2,3);
print "数组大小: ",标量 @array,"\n";

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

#!/uer/bin/perl

@array = (1,2,3);
$array[50] = 4;

$size = @array;
$max_index = $#array;

print "数组大小:  $size\n";
print "最大索引: $max_index\n";

Execute the above program, the output result is:

数组大小:  51
最大索引: 50

As can be seen from the output results, there are only four array elements, but the array size is 51.

---

Add and remove array elements

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

If you have no programming experience before, you may ask what a function is. In fact, the print we used before is an output function.

The following table lists the commonly used operation functions in arrays:

Serial number	Type and description
1	push @ARRAY, LIST Push the value of the list to the end of the array
2	pop @ARRAY Pop the last value of the array and return it
3	shift @ARRAY Pop the first value of the array and return it. The index value of the array is also decremented by one.
4	unshift @ARRAY, LIST Put the list in front of the array and return the elements of the new array number.

Example

#!/usr/bin/perl

# 创建一个简单是数组
@sites = ("google","php","taobao");
print "1. \@sites  = @sites\n";

# 在数组结尾添加一个元素
push(@sites, "baidu");
print "2. \@sites  = @sites\n";

# 在数组开头添加一个元素
unshift(@sites, "weibo");
print "3. \@sites  = @sites\n";

# 删除数组末尾的元素
pop(@sites);
print "4. \@sites  = @sites\n";

# 移除数组开头的元素
shift(@sites);
print "5. \@sites  = @sites\n";

Execute the above program, the output result is:

---

##Cut array

We can cut an array , and return the new array after cutting:

#!/usr/bin/perl

@sites = qw/google taobao php weibo qq facebook 网易/;

@sites2 = @sites[3,4,5];

print "@sites2\n";

Execute the above program, the output result is:

weibo qq facebook

The array index needs to specify a valid index value, which can be a positive number followed by a negative number, each index value Separate with commas.

If it is a continuous index, you can use

.. to indicate the specified range:

#!/usr/bin/perl

@sites = qw/google taobao php weibo qq facebook 网易/;

@sites2 = @sites[3..5];

print "@sites2\n";

Execute the above program, the output result is:

weibo qq facebook

---

Replace array elements

The splice() function is used to replace array elements in Perl. The syntax format is as follows:

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

Parameter description:

• @ARRAY : The array to be replaced.

• OFFSET: Starting position.

• LENGTH: The number of elements to replace.

• LIST: List of replacement elements.

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

#!/usr/bin/perl

@nums = (1..20);
print "替换前 - @nums\n";

splice(@nums, 5, 5, 21..25); 
print "替换后 - @nums\n";

Execute the above program, the output result is:

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

---

Convert a string to an array

In Perl, use the split() function to convert a string to an array. The syntax format is as follows:

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

Parameter description:

• PATTERN: delimiter, default is space.

• EXPR: Specify the number of strings.

• LIMIT: If this parameter is specified, the number of elements in the array is returned.

Example

#!/usr/bin/perl

# 定义字符串
$var_test = "php";
$var_string = "www-php-com";
$var_names = "google,taobao,php,weibo";

# 字符串转为数组
@test = split('', $var_test);
@string = split('-', $var_string);
@names  = split(',', $var_names);

print "$test[3]\n";  # 输出 com
print "$string[2]\n";  # 输出 com
print "$names[3]\n";   # 输出 weibo

Execute the above program, the output result is:

o
com
weibo

---

Convert the array to a string

In Perl, the join() function is used to convert an array into a string. The syntax format is as follows:

join EXPR, LIST

Parameter description:

• EXPR: connector.

• LIST: List or array.

Example

#!/usr/bin/perl

# 定义字符串
$var_string = "www-php-com";
$var_names = "google,taobao,php,weibo";

# 字符串转为数组
@string = split('-', $var_string);
@names  = split(',', $var_names);


# 数组转为字符串
$string1 = join( '-', @string );
$string2 = join( ',', @names );

print "$string1\n";
print "$string2\n";

Execute the above program, the output result is:

www-php-com
google,taobao,php,weibo

---

Array sorting

Array sorting in Perl Use the sort() function, the syntax format is as follows:

sort [ SUBROUTINE ] LIST

Parameter description:

• SUBROUTINE: Specify the rule.

• LIMIT: list or array.

Example

#!/usr/bin/perl

# 定义数组
@sites = qw(google taobao php facebook);
print "排序前: @sites\n";

# 对数组进行排序
@sites = sort(@sites);
print "排序前: @sites\n";

Execute the above program, the output result is:

排序前: google taobao php facebook
排序前: facebook google php taobao

Note: Array sorting is based on ASCII numeric values. So when we sort the array, it is best to convert each element to lowercase before sorting.

---

Special variables: $[

Special variables

$[ represents the first index value of the array, which is generally 0. If we $[ is set to 1, then the first index value of the array is 1, the second is 2, and so on. The example is as follows:

#!/usr/bin/perl

# 定义数组
@sites = qw(google taobao php facebook);
print "网站: @sites\n";

# 设置数组的第一个索引为 1
$[ = 1;

print "\@sites[1]: $sites[1]\n";
print "\@sites[2]: $sites[2]\n";

Execute the above program, the output result is:

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

Generally, we do not recommend the use of special variables

$[. In the new version of Perl, This variable is obsolete.

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Merge arrays

The elements of the array are separated by commas. We can also use commas to merge arrays, as shown below:

#!/usr/bin/perl

@numbers = (1,3,(4,5,6));

print "numbers = @numbers\n";

Execute the above program, the output result is:

numbers = 1 3 4 5 6

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

#!/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

---

Select elements from the list

A list can be used as an array, and the specified element can be read by specifying the index value after the list, as follows:

#!/usr/bin/perl

$var = (5,4,3,2,1)[4];

print "var 的值为 = $var\n"

Execute the above program, the output result is:

var 的值为 = 1

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

#!/usr/bin/perl

@list = (5,4,3,2,1)[1..3];

print "list 的值 = @list\n";

Executing the above program, the output result is:

list 的值 = 4 3 2