11 1 Cookies CGI/Perl Programming By Diane Zak

11 2 Objectives In this chapter, you will: Learn the difference between temporary and persistent cookies Create a cookie Send a cookie to a web browser Access the information stored in a cookie

11 3 Introduction Misconceptions about cookies: –Contain viruses –Gain access to private information stored on a computer Truth about cookies: –Cookie are just pieces of text Since they are not programs, they cannot pass a virus or read a hard disk

11 4 Introduction –Cookies only contain information that has been disclosed on the cookie’s website –A web site can only access information stored in its cookie Does not have access to any other site’s cookie files

11 5 Using a Cookie A cookie is a piece of data that a Web server stores in your computer –Stored in RAM Random Access Memory –Store on hard drive –Allows site to remember information about you Data entered on a form Number of times a site has been visited User preferences

11 6 Using a Cookie Every cookie can contain: –Required key and value –Optional information like expiration date 2 types of cookies: –Temporary cookie Also referred to as a session cookie Stored in RAM (Random Access Memory) Only exists while browser is open Erased from memory when the browser is closed

11 7 Using a Cookie 2 types of cookies: –Permanent cookie Stored in a text file Has expiration date telling browser when the cookie should be deleted Netscape stores in cookies.txt file –In Netscape directory Internet Explorer stores each cookie in a separate file –Each file name starts with your username –In Cookies directory

11 8 Using a Cookie Browser’s responsibilities: –Web browser keeps track of all cookies sent to it by a particular server –When a URL is typed into a browser, the browser searches RAM and the hard drive for any cookies belonging to the server Contacts server and transmits any cookies and the URL CGI.pm module contains functions for creating and retrieving cookies

11 9 Creating a Cookie cookie function: –Syntax: cookie (-name => key, -value => value, -path => path, -expires => expires); The => operator is the “corresponds to” operator. –Used to associate each argument with a value –Can use comma instead

11 10 Creating a Cookie PartsDescription key- Required - Name of value listed in –value - Can be string, number, scalar variable value- Required - Value of the cookie - Can be string, number, scalar variable, array, or hash path-Optional - Indicates the scripts to which the cookie will be sent - If omitted, sent to all scripts on server expires- Optional - When the cookie will expire - If omitted, will expire when the browser is closed

11 Creating a Cookie Expiration Settings: SettingCookie will expire +ns+nsin n seconds +nm+nmin n minutes +nh+nhin n hours +nd+ndin n days nowimmediately +nM+nMin n months +nY+nYin n years

11 12 Creating a Cookie

11 13 Sending a Cookie to the Browser header function: –Part of CGI.pm –Sends one or more cookies to a browser –The header function already sends the print “Content-type: text/html\n\n”; statement If it is typed into the script before the header function, the cookies will not be sent to the browser –Cookies must be sent before the Content-type header line is processed

11 14 Sending Cookies to a Browser

11 15 Accessing the Information Stored in a Cookie When a URL is entered into a browser: –Browser searches RAM and hard drive for cookies for that server –Browser contacts server and sends cookies, URL, and any form data –Server sends cookie and form data to script if the URL is associated with a script

11 16 Accessing the Information Stored in a Cookie Syntax: –cookie (key) Example: $color = cookie(‘Color’); print “ \n”; The value of the Color key is assigned to the $color variable –When the cookie was created, its name was “Color”, and its value will change the background color of a dynamic web page

11 17 Examples: $custid = cookie(‘Id’); print “Customer id: $custid = split (/ /, cookie(‘Record’)); foreach my $rec { print “$rec \n”; } If the value associated with the cookie’s key is an array: Use split to divide the value associated with the key Use the foreach loop to go print each element Accessing the Information Stored in a Cookie

11 18 The Jubilee Book Club Web Pages If the user has never visited the site, the Name text box should be blank If the user has visited the site, his/her name should appear in the Name text box

11 19 The Jubilee Book Club Web Pages

11 20 Planning and Coding the book2.cgi Script –Each time the user visits the web site, the book2.cgi script will create the Name cookie and send it to the user’s browser –It will overwrite the existing Name cookie (if any) –The cookie will expire in 6 months

11 21 Planning and Coding the book1.cgi Script

11 22 Planning and Coding the book1.cgi Script

11 23 Summary A cookie is a piece of data that a Web server can store on your computer (RAM, hard drive) depending on the life span of the cookie. A cookie cannot pass a virus or read a hard drive. A cookie can contain only as much information as you disclose on the web site that creates the cookie. Every cookie has a key and value and can contain optional information like path and expiration date.

11 24 Summary A temporary (session) cookie is stored in RAM and erased from memory when the browser is closed. A persistent cookie is stored in a text file on the hard drive. –Expiration date telling browser when to delete Like form data, cookies are sent with the requested URL. The cookie function, defined in CGI.pm, can create a cookie or access data stored in a cookie.

11 25 Summary cookie function: –must specify –name and –value functions. –The => operator is called the “corresponds to” operator. –The –path argument determines which scripts receive the cookie. –The –expires argument indicates the expiration period for the cookie. You can use the header function to send one or more cookies to a browser –Defined in cgi.pm –Sends cookie information and the Content-type header line to the browser Don’t need to type in the Content-type header line