3
Sending Data
Using an Online
Form
CGI/Perl
Programming
By Diane Zak
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3
Objectives
• In this chapter, you will:
• Plan and create a CGI script that
processes form data
• Learn how to prevent Perl from
creating undeclared variables in a
script
• Declare and create scalar variables in
a script
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3
Objectives
• In this chapter, you will:
• Use assignment statements to
assign values to existing variables
• Send form data to a script using
GET and POST
• Improve the appearance of
numbers displayed on a Web page
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Introduction
3
• Online forms can also be used to
send data to a CGI script, in addition
to hyperlinks
• Online forms are written in HTML
• Information is sent through a form by
clicking on the submit button
• Typically, after the data has been
submitted, a script will create a
dynamic Web page that contains an
appropriate response, such as:
– Acknowledgment
– Answer
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3
Processing Form Data
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Processing Form Data
3
1. When the Submit button is clicked, the
browser sends the form data to the server
2. The server forwards the form data to the
CGI script to process
3. The CGI script sends its output to the
server
4. The web server transfers the HTML code6
to the browser which displays it for the user
Planning a Script
3
• It is important to plan a script beforehand
– Errors can be difficult to find
• Steps to planning:
1. Determine the script’s input and output
• Input may be the form data
2. List the steps for the script to transform
the input into output
• Algorithm
– A set of step-by-step instructions to solve a problem
– Written in pseudocode or flowchart
3. Code the algorithm in a language that
the computer will understand
• Like Perl
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3
Variables in Perl
• Variable
– Location in the computer’s internal
memory where a script can temporarily
store data
– Each variable has a data type
• Determines the kind of data the variable can
store
• Perl has 3 data types:
– Scalar variable – can store one value
» Example: number or string
– Array variable – can store lists or sets of
values
– Hash variable – can store lists or sets of values
– Each variable has a name
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3
Variables in Perl
• Scalar variable naming:
– Must begin with dollar sign ($)
– Followed by a letter
– Optionally followed by one or more
letters, numbers, or underscores
– Valid names: $city, $inc_tax
– Variable names are case-sensitive:
• $city and $CITY are two different variables
– Should use descriptive names
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Variables in Perl
3
• Perl does not require variables to be
explicitly declared
– By default, variables are created “on the
fly”
• Variable exists as soon as you use the
variable
– It is a good programming practice to not
allow variables to be created “on the fly”
• use strict;
– Prevents Perl from creating undeclared
variables
• Syntax to declare variables:
– my (variablelist);
• Example:
– my ($hours, $gross, $sales);
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3
Assignment Statements
• Can be used to assign or change a value
stored in a variable
– Interpolation occurs in the fourth example:
• Perl replaces the variable’s name with the
variable’s contents
• If a variable name occurs within double quotes (“)
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in a statement, the value of the variable will be
replaced for the variable’s name
Coding the Bonus
Calculator Script
3
• 4 scalar variables are used:
– $name, $sales, $rate, $bonus
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Coding the Bonus
Calculator Script
3
• The lower precedence number will be
performed before a higher precedence
number
• The negation operator is a unary operator –
it makes a number negative, rather than
the subtraction binary operator which
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subtracts one number from another
Coding the Bonus
Calculator Script
3
• If operators have the same precedence
number, the operators are evaluated
from left to right
• Parentheses can be used to change the
order that operators are evaluated
• The modulus operator (%) is used to get
the remainder of the division of two
integers
– Example:
• 211 % 4 = 3
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3
Accessing the Values
Received from an Online Form
• Each data item sent by a hyperlink has
a key and value
• Online forms also use keys and values
– key = name of the form element
– value = data entered by user
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3
Accessing the Values
Received from an Online Form
• Data sent
using an
online form
must also be
parsed by the
script
– Can use same
parsing
routing in
CGI.pm
• param
function
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The Bonus Calculator
Form
3
• The <FORM> tag uses 2 properties:
– ACTION
• The name of the CGI script that will process
the form data
– METHOD
• Controls how your web browser sends the
form data to the Web server
• GET
– Default method
– Appends form data to the end of the URL
– Similar to sending data using a hyperlink
• POST
– Sends form data in a separate data stream
– Safer than GET
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» Some web servers limit the size of the URL
3
The Bonus Calculator Form
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3
The Bonus Calculator Form
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Including a Dollar Sign
in a Number
3
• Use the backslash (\) followed by the
dollar sign ($) in a print statement
– Backslash is used because the dollar
sign has special meaning in Perl (scalar
variables)
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Including a Dollar Sign
in a Number
3
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Using the printf
function
3
• The printf function can be used to
format data
– Can specify the number of decimal
places
– Can display a plus sign (+) before
positive numbers and a minus sign (-)
before negative numbers
– Syntax:
• printf formatstring, list;
– formatstring = string that controls the
appearance of each item in the list
» Can contain text and one or more format
fields
– list – comma-separated list of items, mostly
variables
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Using the printf
function
3
• 2 format fields are used in the
formatstring
– %.1f
• Format the value stored in $avg1 variable
• Display the value as a floating-point number with 1
decimal place
– %.2f
• Format the value stored in $avg2 variable
• Display the value as a floating-point number with 223
decimal places
Using the printf
function
3
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Using the printf
function
3
25
3
Using the printf function in
the Bonus Calculator Script
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Summary
3
• When you click the submit button, the browser
sends the form data to the server.
– If the form is associated with a CGI script, the
server forwards the form data to the script for
processing.
– When the script has finished processing, it sends
its output – typically HTML – to the server, which
transfers the output to the browser.
• Planning a CGI script involves determining the
script’s input, output, and algorithm.
• A variable is a location, within the computer’s
memory, where a script can temporarily store
data.
– Every variable has a data type and name.
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Summary
3
• Perl provides 3 basic data types for variables:
– scalar – stores one value – normally number or
string
– hash
– array
• Scalar variable names begin with dollar sign
($), followed by a letter, and optionally one or
more letters, numbers, or underscores.
– Variable names are case-sensitive.
• use strict; can be used to stop Perl from
creating variables “on the fly” to force
declaration of variables
• my (variablelist) is used to explicitly declare
variables
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Summary
3
• An assignment statement is used to assign
or change a value of a variable
– Syntax: variable = value;
• When the name of a variable appears within
double quotation marks in a statement, Perl
replaces the variable’s name with the
variable’s contents – interpolation.
• Single quotation marks around a string
indicate that no interpolation should be
performed.
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Summary
3
• You can use the parsing routine contained
in the CGI.pm module to parse the data
submitted to a script using an online form.
• You can use the printf function to format
data displayed on a web page.
– printf formatstring, list;
– formatlist – string that controls appearance of
each item in list
– list – comma-separated list of items whose
values you want to format
• A format field in a printf function’s
formatstring is composed of 5 parts:
– %, modifier, minimum field width, precision, and
format type
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– Only % and format type parts are required.