Perl array

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

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

Example

#!/usr/bin/perl @hits = ( 25 , 30 , 40 ) ; @names = ( " google " , " codercto " , " 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 , allowing it to be output as is.

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

create array

Array variables start 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/This is an array/;

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/googletaobao...codercto/;

You can also assign values ​​to an array by index, as follows:

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

Access array elements

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

Example

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

 googletaobaocoderctocodercto

Array index values ​​start from 0, that is, 0 is the first element, 1 is 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 an array format that can be output in sequence. The format is starting value + .. + end value . The example is as follows:

Example

#!/usr/bin/perl @var_1 0 = ( 1 . .10 ) ; @var_2 0 = ( 10 . .20 ) ; @var_abc = ( a .. z ) ; print " @var_10 n " ; # Output 1 to 10 print " @var_20 n " ; # Output 10 to 20 print " @var_abc n " ; # Output a to z

 1 2 3 4 5 6 7 8 9 1010 11 12 13 14 15 16 17 18 19 20a bcdefghijklmnopqrstuv wxyz

array size

The array size is determined by the scalar context within the array. :

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

The array length returns the physical size of the array, not the number of elements. We can see 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 " ;

 Array size: 51 Maximum index: 50

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

Add and remove array elements

Perl provides some useful functions for adding and removing 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 commonly used operation functions in arrays:

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

Example

#!/usr/bin/perl #Create a simple array @sites = ( " google " , " codercto " , " taobao " ) ; print " 1. @ sites = @sites n " ; # Add an element to the end of the array push ( @sites , " baidu " ) ; print " 2. @ sites = @sites n " ; # Add an element to the beginning of the array unshift ( @sites , " weibo " ) ; print " 3. @ sites = @sites n " ; # Delete elements at the end of the array pop ( @sites ) ; print " 4. @ sites = @sites n " ; # Remove elements at the beginning of the array shift ( @sites ) ; print " 5. @ sites = @sites n " ;

Cut array

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

Example

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

 weibo qq facebook

Array index needs to specify a valid index value, which can be a positive number followed by a negative number. Each index value is separated by a comma.

If it is a continuous index, you can use .. to indicate the specified range:

Example

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

 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: 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 an array starting from the 6th element:

Example

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

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

Convert string to array

To convert a string into an array in Perl, use the split() function. The syntax 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 #define string $var_test = " codercto " ; $var_string = " www-codercto-com " ; $var_names = " google,taobao,codercto,weibo " ; # Convert string to array @test = split ( ' ' , $var_test ) ; @string = split ( ' - ' , $var_string ) ; @names = split ( ' , ' , $var_names ) ; print " $test [3] n " ; # Output o print " $string [2] n " ; # Output com print " $names [3] n " ; # Output weibo

 ocomweibo

Convert array to string

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

 join EXPR, LIST

Parameter description:

EXPR: Connector.

LIST: List or array.

Example

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

 www-codercto-comgoogle,taobao,codercto,weibo

Array sort

Array sorting in Perl uses the sort() function, and the syntax is as follows:

 sort [SUBROUTINE] LIST

Parameter description:

SUBROUTINE: Specify rules.

LIST: List or array.

Example

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

 Before sorting: google taobao codercto facebook After sorting: facebook google codercto 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: $[

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

Example

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

 Website: google taobao codercto facebook@sites[1]: google@sites[2]: taobao

In general, we do not recommend using the special variable $[ . In the new version of Perl, this variable has been abandoned.

Merge arrays

The elements of the array 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 " ;

 numbers = 1 3 4 5 6

It is also possible to 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 " ;

 numbers = 1 3 5 2 4 6

Select element from list

A list can be used as an array. Specifying the 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 "

 The value of var is = 1

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

Example

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

 value of list = 4 3 2