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Array and Hash Variables

CGI/Perl Programming

By Diane Zak

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Objectives

• In this chapter, you will:

• Create an array• Access the variables in an array• Create a hash• Access the variables in a hash• Learn how to code the repetition

structure using the foreach and for statements

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Introduction

• Perl has 3 data types for variables:– scalar

•Can store 1 value

– array•Can store multiple values

– hash•Can store multiple values

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Juniper Printers Script

• Planning and Coding:

• Output:

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Juniper Printers Script

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Array Variables

• Array Variable or Array– Group of related scalar variables,

each having the same name– Index is used to distinguish the scalar

variables within the array• The index is assigned as the area is

created• Index starts with 0 for the first variable• Index is also known as a subscript

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Array Variables

• Array declaration syntax:– my arrayname=(list);

• Name of array must begin with at sign (@)• After the @, the name must start with a

letter, and then a combination of letters, numbers, or underscores

• The list consists of values separated by commas

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Array Variables

• Array declaration examples:– my @sales = (25000, 35000, 10000);– my @cities = (“Boston”, “Chicago”,

“Detriot”, “San Diego”);

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Array Variables

• Accessing the array– Replace the @ in the array name with a $,

array name, index enclosed in square brackets ([ ])

– Example:– my @sales = (25000, 35000, 10000);

• $sales[0]=25000• $sales[1]=35000• $sales[2]=10000

– A scalar variable within an array can be used the same as any other scalar variable

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Using an Array in the Juniper Printers Script

• The customer will be sending the model number from the form– 0, 1, or 2

• This number corresponds to the index number of the @models array

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Using an Array in the Juniper Printers Script

• This code now includes declaring the @models array, as well as accessing and printing the corresponding model name

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Hash Variables• Hash variable, or hash:

– Collection of related scalar variables– Like an array variable– Instead of using an index number, a

hash uses a key name– Like an array’s index numbers, the keys

are assigned to the scalar variables when the hash is created

– Another name for a hash is an associative array

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Hash Variables

• Hash declaration syntax:– my hashname = (key1, value1, key2,

value2,...keyn, valuen);• Name of hash must start with percent

sign (%)• After %, the name must start with a

letter, and then a combination of letters, numbers, or underscores

– Can declare the hash in one line, or multiple lines

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Hash Variables

• Hash declaration example:– my %sales = (“Jan”, 25000,

“Feb”, 35000, “Mar”, 10000);

– “Jan”, “Feb”, and “Mar” are keys– Their corresponding values are

25000, 35000, 10000

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Hash Variables

• Hash declaration example:– my %cities = (“617”, “Boston”,

“312”, “Chicago”, “313”, “Detroit”, “619”, “San Diego”);

– Keys: “617”, “312”, “313”, “619”– Values: “Boston”, “Chicago”, “Detroit”, “San

Diego”

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Hash Variables• Accessing the hash:

– Replace the % in the hash name with a $, array name, key enclosed in braces ({ })

– Example:– my %sales = (“Jan”, 25000,

“Feb”, 35000, “Mar”, 10000);

• $sales{Jan} = 25000• $sales{Feb} = 35000• $sales{Mar} = 10000

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Hash Variables

• Accessing the hash:– If a key has a space:

• Use single or double quotation marks within the braces

• Example:– $state {‘New Mexico’}– $state {“New Mexico”}

– A scalar variable within a hash can be used the same as any other scalar variable

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Using a Hash in the Juniper Printers Script

• The customer will be sending the letter corresponding to the Operating System

• The system letter will be stored in the $sysletter variable

• To access the full operating system name, the $sysletter key can be used with the %systems hash– $systems {$sysletter}

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Using a Hash in the Juniper Printers Script

• This code now includes declaring the %systems hash, and printing out the full operating system name by accessing the %systems hash

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Modifying the Juniper Printers Form and Script

• HTML checkboxes:– Use the same key, in this form, System– Syntax:

• <INPUT TYPE=checkbox NAME=name VALUE=value>

• The CHECKED keyword can be used to have a checkbox checked by default

– If multiple checkboxes are selected, the keys and values are sent to the script

• Example:• If all 3 operating systems are selected:

System=W&System=M&System=U will be passed

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Modifying the Juniper Printers Form and Script

• One change made involves storing the System key in @sysletter array instead of $sysletter, due to the possibility of multiple values for that key

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Modifying the Juniper Printers Form and Script

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The foreach and for Statements

• 3 basic structures (control or logic structures) make up scripts:– Sequence

• Script statements are processed in the order they appear in the script

– Selection• Make a decision or comparison, and then select one

of 2 paths based on the result

– Repetition (loop)• Repeat a block of instructions for a specified

number of times or until a condition is met• Examples: foreach, for, while, until

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The foreach and for Statements

• foreach:– The foreach statement repeats one or more

instructions per element in a group, like an array

– When each member of the array has been processed, the loop stops

– Syntax:foreach element (group) {

One or more statements processed per element in group

}

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The foreach and for Statements

• foreach– Example:

my ($num, @numbers);

@numbers = (5000, 200, 100, 3);foreach $num (@numbers) {

print “$num<BR>\n”;}

Result:

5000

200

100

3

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The foreach and for Statements

• for:– The for statement is used to repeat one or

more statements as long as the loop condition is true

– 3 arguments are used:• initialization argument

– counter variable• loop condition

– Boolean expression that evaluates to true or false– Loop stops when loop condition evaluates to false

• update– Updates the counter variable in the initialization

argument

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The foreach and for Statements

• for:– Syntax:

for (initialization; loop condition; update) {one or more statements to be processed as long as the loop condition is true

}

– Example:my $num;for ($num = 1; $num < 4; $num = $num + 1) {

print “$num<BR>\n”;

}

Result:

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3

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Updating the Juniper Printers script

• foreach will be used to process each member of the @sysletter array

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Summary• keys are the names of the form elements.

– values of the keys will be passed to the server– Textbox: value is the text entered– Radio button or checkbox: value assign to the VALUE property

of the selected radio button or checkbox

• Array variable, or array, is a group of related scalar variables.– Each scalar variable in array has same name, but unique index

number– First scalar variable in array has index number of 0

• Array declaration: my arrayname = (list);

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Summary• Array name must start with at sign (@), followed by

letter, then optionally one or more letters, numbers, or underscores

• When referring to scalar variable in an array, replace @ with $, then the name, along with the index enclosed in square brackets ([ ])

• Hash variable, or hash, is a group of related scalar variables. Each scalar variable has same name, but unique key

• Hash declaration: my hashname = (key1, value1, key2, value2, ... keyn, valuen);

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Summary

• Name of hash must start with percent sign (%), followed by letter, then optionally one or more letters, numbers, or underscores

• When referring to scalar variable in a hash, replace % with a $, and follow the name with the scalar variable’s key in braces ({ }).

• A repetition structure, or loop, is used to tell the computer to repeat a block of instructions:– Certain number of times– Until a condition is met

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Summary

• foreach statement can be used to repeat one or more instructions for each element in a group

• for statement can be used to repeat one or more statements for as long as loop condition is true