1. Ch27 - Common Gateway Interface (CGI) and Perl
Outline
Server-side processing
Common Gateway Interface (CGI)
Other server-side programming technologies
(Active Server Pages (ASP))
Java Servlets and Java Server Pages (JSP)
PHP Hypertext Processor
Python
Perl
Simple Perl examples
Handling HTTP Requests – GET and POST
CGI Environment Variables
Viewing CGI Environment Variables in Perl
Using Perl DBI to Connect to a Database
(Hel sida välj 75%, Stlk 9 OK)
Dynamic creation of Web pages – the key to interactivity and performing transactions on the web
The web page is based on data submitted by the user
E.g. results page from search engines and order confirmation pages at on-line stores
The web page is derived from data that changes frequently
E.g., a weather report or a news headlines page
The web page uses information from databases or other server-side resources
E.g. an e-commerce site could build a Web page that lists the current price and availability of each item that is for sale
Going dynamic – an overview of technologies for dynamic web programming
På kursen lär vi oss inte Perl utan kommer bara använda en bråkdel för att illustrera principerna för CGI
Not covered
Web Server Extensions (using ISAPI, NSAPI)
(String Processing and Regular Expressions)
(Server-Side Includes)
(Verifying a Username and Password)
(Form Processing and Business Logic)
(Cookies and Perl)
(Operator Precedence Chart)
(Internet and World Wide Web Resources)

2. Web Programming Technologies
Content
Authoring:
HTML
Protocols:
HTTP
Client Side Processing
Server Side Processing
Client-Side Processing vs Server-Side Processing - Putting it All Together
Många tekniker som vill bli standarder
Börjar rensas upp och de-facto standarder skapas
Har växt enormt under 1990-talet
1990- statiska webbsidor, (Web servers were originally designed to serve static HTML pages) enklare dynamiska webbsidor - Utveckling främst I Perl, asvancerade dynamiska webbsidor - Integration med andra program, webbapplikationer - E-handel, ASP, avancerade webbapplikationer - PHP
Webbapplikation
Relativt nytt begrepp för en avancerad dynamisk webbsida
Webbapplikation – grundpelare (CGI och formulär, Java)
Lägeslös miljö ( sessioner, cookies)
Lagring av data (Databas)
A program is a sequence of written instructions which is compiled and executed by a computer
A script is a program which runs directly without pre-compilation
Web pages can be thought of as scripts which are interpreted by web browsers
Creating HTML pages and organizing them into web sites (HTML, DHTML,XML)
Where should my functionality reside? Server-side or client-side?
Server-side technologies (CGI, mod_perl, s/s JavaScript, PHP, JSP, ASP)
Scripting on the server side for content delivery (Perl, ASP)
Client-side technologies
Scripting on the client side for interactive content (Javascript). JavaScript most popular client-side script
Programming on the client side and server side (Java) - ?
Client-side scripting
Validates user input, Accesses the browser, Enhances Web pages with ActiveX® controls, applets, etc., Manipulates browser documents
Client-side validation
Reduces number of requests that need to be passed to server
Client-side scripting limitations
Browser dependency, Viewable to users through View Source command
Client-server communication relies on network protocols. HTTP handles transfer of web pages. Server processing can be handled be CGI-protocol
HTTP Request
Web
Server
Web
Browser
HTML Pages
CLIENT
SERVER
Client Scripts:
JavaScript
Client Programs:
Java Applets
HTTP Response
HTML Page
Server Scripts:
Perl, ASP,
PHP, JSP
Protocols: CGI
Server Programs:
Java Servlets

3. What is server-side processing?
The use of programs on the server-side to process client input and produce client output
Generates custom responses for clients
Has access to server-side software that extend server functionality
Provides programmers greater flexibility
Contains greater programmatic capabilities than client-side equivalents
There are several technologies that can be used to create server-side scripts
Common Gateway Interface (CGI)
Microsoft Active Server Pages (ASP) – HTML embedding VBScript
PHP Hypertext Processor (PHP)
Java Servlets and Java Server Pages (JSP)
Common script languages
Perl, VBScript, Python, Java
Exekvering på server istället för på klient. Server-side processing of HTML data such as form input
• Kan göra exekveringen säkrare (ur både klient och serverhänseende). Kräver inget speciellt av klienten (plug-ins etc)
Server-side scripts
Ger tillgång till kataloger, filer och andra program på servern
Has access to server-side software that extend server functionality
What needs to be on the server side?
Any functionality that uses the web to change the status of a database or file system on the server side, e.g., online shops back-ends, online booking systems
Any functionality that requires access to resources not available on the client (e.g., search engines, web-cam, etc.)
Any functionality designed to safeguard the security of the server
Anything else that can’t or shouldn’t be done on the client
What shouldn’t be on the server side?
Functionality that can be implemented on the client side without compromising server security. Will usually make your site appear faster!
Applications that are to handle sensitive data on the client that are not to be shared with the server. Acceptance issues!
Webbutveckling bedrivs vanligen i interpreterande språk ex. Perl, ASP och PHP
Enklare att hantera i moderna webbspråk, exempelvis PHP och ASP. Hastigheten är inte så betydelsefull
Other forms of server side processing
Web Server Extensions (using ISAPI, NSAPI) Ny? LT 5-6 Web Server Extensions
SSI

4. Common Gateway Interface (CGI)
A standard for how a web server interact and transfer information to an application program (called CGI script)
Application is responsible for generating some dynamic content
Application can call database
Extend servers beyond simple HTML file serving
CGI = Common Gateway Interface.
Common - supported by almost all web servers, can be used by many platforms and programming languages such as Perl, C, C++, VBScript, etc
Gateway - pathway between server and application programs
Interface - provides a well-defined way to call up its features
CGI is Not…
a programming language
AL –11Se ävenLT 5-6
Example uses for CGI
Forms
On-the-fly Pages
Database Interaction
Logging/Counters
Animation
CGI is…
a gateway which allows programs or scripts written in either languages to run over the internet
Gateway:
potential access it offers to other systems ( a standard environment)
Gateway program (CGI) on server gets data from client and passes it to a CGI application
Practically the oldest widespread server-side technology for dynamic generation of content
CGI = protocol, JAVA = programming language
Ett CGI-script kan skrivas i många olika språk, tex Perl, C/C++, TCL, C Shell, Visual Basic, Python, JavaScript (has client-side and server-side parts, part of Netscape servers ), (Java, Smalltalk) och AppleScript
Which one you prefer depends on your background
C and C++ must be compiled code is not platform dependent
Because CGI-applications tend to be fairly trivial large languages such as C++ are often overkill

5. CGI at work Web Server Client (Browser) CGI script
Read explicit data (form data) and implicit data (request headers) sent by client
Generate the results and send explicit data (HTML) and implicit data (status code and response headers) back to client
Client (Browser)
Web Server
2. Sets data
Environment
variables
1. Sends HTTP-request
HTML-
Form
Se även Calgary eller LT 5-12 CGI Operation: A Closer Look
Many CGI scripts access databases – but we focus on the CGI script communication with server
Connection established
Server receives client request for script via GET or POST (Parameters can be passed to the program.)
Request is sent by clicking buttons or links
Instead of path to a file, the resource specifies a program to be executed.
Server starts script as an external process and passes any client data via environment variables
A web server usually holds many CGI scripts
Script can access environment variables and outputs document
Script process and makes decisions on data
Output is piped to server, which may parse it and transmits it back to client
Connection closed (HTTP is stateless)
CGI-programs generally executes then quits and is restarted each time is it needed.
CGI Web Server Interaction
User invokes a script
Request and Relay data
CGI script wakes up
Carry out request
Return request to server
Send results back to user
User sees and/or hears results
4. Reads data
Internet
CGI script
3. Calls
script
6. Sends HTTP-response
(HTML Page)
5. Returns output
Database

6. CGI Advantages and Disadvantages
Web server and language independence (such as C/C++ or Perl)
Wide acceptance. De facto standard (One of the earliest server-side options). Many free example CGI scripts
Simple to use
Disadvantages
Each request starts up a new process of the CGI script
Stateless protocol. Can’t retain information between requests
Communication to application must go through the web server
Advantages (se AL 15):
Vast majority of Web servers run Unix. Majority of servers does not support ASP at the moment.
Web masters want free software with wide range of technical support in the Internet.
Nackdelar
Långsamt jämfört med ASP och PHP (resource intensive)
Går ej att kompinera HTML och scriptkod eftersom scriptkoden måste ligga I en separat fil
Helt enkel föråldrat (Karlstad)
Why is state hard for Perl/CGI?
HTTP is stateless.
Each CGI invocation starts a new process.
No association between HTTP connections.
When clientsat an on-line store add an item to their shopping chart, how does the server know what’s already in the chart?
When clients decide to proceed to checkout, how can the server determine which preciously created shopping cart is theirs?
Solution
cookies:
Introduced by Netscape
Not actually part of official HTTP specification.
Basic idea:
“Set-cookie” header in HTTP response defines a cookie providing: value, name, domain, path
Client sends cookie value and name in request header when domain and path match.
Good when state must survive the current session.
What about security?
Prone to security problems
Client attacking the program to gain unauthorized access
Innocent script = dangerous to the integrity of a system

7. Java Servlets and Java Server Pages (JSP)
Java servlet is like an applet that runs inside a web server, extending the servers functionality
A web server must provide an API so Java servlets can be written
JSP is part of the servlet API that allows Java to be embedded inside HTML
Same concept as ASP
Advantages of servlets and JSP
When written in Java, servlets and JSP are plattform independent
Wide support: from Netscape, Sun, Apache, Oracle, IBM
Servlets and JSPs are compiled, loaded once at server startup, and service Web requests using separate lightweight threads
Java Servlets and JSP are part of Java 2 Enterprise Edition (J2EE), a collection of enterprise APIs
Se Deitel ch 30 och 31, även AL-24, LT 5-9
Servlets
Javas motsvarighet till CGI fast anpassat till Java
The servlet API is defined by Sun Microsystems
JSP
Similar to ASP or PHP in terms of ability to separate static and dynamic content
In-process
Easier to run offline (container)
Platform-independent
Java is becoming very popular as a server-side language
Servlets/JSP provide high performance
Java is portable and supported by many servers
Biggest difference between CGI applications and servlets is that a servlet is persistent.
each user request is invoked as a thread
once it is started, it stays in memory and can fulfill multiple requests
makes them faster because there's no wasted time in setting up and tearing down the process

8. PHP Hypertext Preprocessor
PHP is a script language in Web programming, which is platform independent but used primarily on Linux Web servers
Initials come originally from the earliest version of the program, which was called "Personal Home Page Tools“. Now acronym for PHP Hypertext Preprocessor
PHP is free and offered under an open source license. The latest version is PHP4.
Interpreter is freely available.
An alternative and works similar to ASP technology
LAMP - Linux, Apache, MySQL and PHP. Four parts to build fast, robust Web applications. PHP is a project of the Apache Software Foundation.
As with ASP, the PHP script is embedded within a Web page along with its HTML. Before the page is sent to a user that has requested it, the Web server calls PHP to interpret and perform the operations called for in the PHP script.
An HTML page that includes a PHP script is typically given a file name suffix of ".php" ".php3," or ".phtml".
Like ASP, PHP can be thought of as "dynamic HTML pages," since content will vary based on the results of interpreting the script.
Se Deitel ch 29,
Står för PHP Hypertext Preprocessor
Ingår i de-facto standarden LAMP (Linux, Apache MySQL, PHP)
Very mature and extensive language
Similar to Perl. Nyare scriptspråk som från början var ett supplement till Perl
Works similar to ASP, but with (to my knowlegde) a larger range of functions
Via CGI or in-process server
Enables separation of static and dynamic content

9. Perl
Perl (Practical Extraction Report Language) is an interpreted language (not compiled, like Java) which is ideally suited for CGI programming.
written by Larry Wall in Combines syntax from several UNIX utilities and languages.
has also been adapted to non-UNIX platforms. ActivePerl, the standard Perl implementation for Windows is freely available
Perl is a text processing language that provides comprehensive string handling functions
designed to handle a variety of system administrator functions
It is widely used to write Web server programs for such tasks as
automatically updating user accounts and newsgroup postings
processing removal requests
synchronizing databases and generating reports
Vad är Perl?
Perl är ett interpreterande programspråk inspirerat av C och cshell (Unix-shell)
Används som scriptspråk, precis som VBscript.
Finns på många plattformar. Perl comes as part of the Unix system. Larry Wall now works for O’Reilly
Kör på Win genom att ladda hem (även bok CD) och installera Perl interpretator, ex ActivePerl
Många funktioner för bla mönstermatchning
Perl approach: TIMTOWTDI There Is More Than One Way To Do It
It has its roots in Unix system administration (similar to Unix, SED, AWK, and Shell Script) and offers several features like regular expressions and file manipulation which make it extremely powerful. It’s arguably the most popular CGI scripting language
Många specialfunktioner för att hitta och byta ut tecken/ord – regular expression
The ActiveState Tool Corporation is the company which develops and maintains ActivePerl, the standard binary Perl distribution for Win32. Is included in book CD
It's learning curve has been described as long and shallow. It is very easy to pick up at first, (går snabbt att konstruera kraftfulla program, especially if you are at all familiar with Unix.
However, it does take quite a bit of time to become familiar with all the little nuances of the language. For most CGI work, however, these little nuances aren't really necessary.
Varför Perl?
Relativt enkelt att använda
Går att provköra som vanligt program från terminal
Finns på flera plattformar
Dock inbjuder inte Perl till välstrukturerade (speciellt stora) program
Troligaste användningsområde: att ta emot data från formulär.
Perl is now an OO language too

10. Python
An interpreted, object-oriented programming language developed by Guido van Rossum.
Can be used to write:
CGI-scripts
ASP-scripts
Large-scale Internet search engines
Small administration scripts
GUI applications
Python is very portable since Python interpreters are available for most operating system platforms.
Although Python is copyrighted, the source code is freely available, and unlike GNU software, it can be commercially re-sold.
Se Deitel ch 28
The name comes from one of van Rossum's favorite television shows, Monty Python's (Pajton) Flying Circus.
Ett alternativ till Perl
Uppbyggt som ett eget språk från grunden till skillnad mot Perl

11. Perl - Simple Example #!/usr/bin/perl $name=“Foo”;
$friends=1; #I only have one friend
#$friends=2; #actually, I have 2 friends
#$friends=“many;” #I have too many friends
if ($friends == 1) {
print “$name, you are my best friend.”; }
The “shebang” construct (#!) indicates the path to the Perl interpreter on Unix systems.
Välj ett scriptexempel
För att testa programmet, skriv perl mitt_program.pl
Perl tolkar koden och skriver ut den i operativsystemet
Observera att det bara fungerar om du installerat Perl på datorn.
Sparas med ändelserna ”.pl” eller ”.cgi”
(#!) Magisk shebang… (magsik rad) The path will vary from system to system.
På Windows är sökvägen utan betydelse. Där associerar man ändelsen med kommandotolken för Perl. Raden tas ändå med för enhetlighets skull.
-         ActiveState install configures the System Registry
Kommentarer med #
Perl is not a strongly typed language you don’t have to declare the type of variable when you declare it
Variabler behöver inte deklareras, aktiveras vid första användandet.
CGI/Perl Hello World
Perl script that returns an HTML document with the text “Hello World”
Remember to make the script executable, and end its name in “.cgi”
#!/usr/local/bin/perl
print “Content-type: text/html\n”;
print “\n”;
print “<html>\n”;
print “<body>\n”;
print “<h1>Hello World!</h1>\n”;
print “</body>\n”;
print “</html>\n”;
Function print writes the string to the screen.

12. Data Types in Perl
Ett tecken symboliserar vilken typ av variabel det är eller %) Ingen risk att blanda variabler och nyckelord
Indexerade variabler börjar
Hash Kallas Tabell på svenska
…Hash consists of a series of pairs of items with each pair comprising of a key and an associated value.
Scalar is a singular data type.
Array is a plural data type
Much of the power of Perl lies in hashes.
Komplettera ev med example #2 (se Calgary)
Ev more advanced exempel med variabler
[mitt_program.pl]
# Att jobba med variabler
Print ”Använda en variabel i en sträng: $var”;
$num = 5;
$test =$num + 5;
Print ”Innehållet i test-variabeln är 10: $test”;
@array = (”Henrik”, ”Kalle”, ”Pelle”) OBS1 ej { som i Java
# Skriver ut Pelle
#Skriver ut hela array

13. Client-Server Interaction
HTTP is a request-response protocol. Client sends request, server responds.
HTTP Request (Client is sending request message to Server ):
When a client sends a request, it consists of three parts:
Request line: (e.g. POST /im269/w7.html HTTP/1/1)
HTTP method type (GET or POST)
Resource name (URL)
Protocol/version
Header: contains browser information (optional)
Message body: in POST method request information is stored here (optional)
HTTP Response (Server is sending response message to Client):
The response sent by the server also consists of three parts:
Response line: (server protocol and status code)
Header: specifies the type of output (content-type such as text/html, location such as or no response such as 204 No Response)
Message body: (the actual data, such as sending back a Web page or a file to the user)
It shouldn’t take a rocket scientist to realize that need to understand HTTP to be effective with CGI
Basic HTTP Exchange
1.Connection established. 2.Client sends a request. 2. Server sends a response. 3.Connection closed.
HTTP Request contains
Request line (includes resource), Request header (Zero or more lines), Request body (ev. FORM data)
HTTP is stateless
The HTTP reply has 3 parts:
Status-Line
Zero or more header lines (Content-length and type)
Tells browser what to do with the information
Content-type (s.k. MIME-huvud)
text/html for html
text/plain for plain text
Location
Status
Message body (HTML-page)
HTTP/ OK < Status line
Date: Fri, 11 Aug :17:44 GMT
Server: Apach/1.3.9 (Unix) (Red Hat/Linux)
Last-Modified: Fri, 11 Aug :17:27 GMT
Etag: “2be71r90-2d ”
Accept-Ranges: bytes
Content-Length: 45
Connection: close
Content-type: text/html < header line
<html>  Message body (HTML-page)
<body>
This is a test
</body>
</html>

14. HTTP Response from a CGI script
A CGI script that produces a HTTP response. CGI responds to the server via standard output
Example CGI scripts:
1. Return content to user
print (“Content-type: text/html”);
print (““);
print (“<HEAD>”);
print (“<TITLE>CGI script output</TITLE>”);
print (“</HEAD>”);
print (“<BODY>”);
print (“<H1>Output from a CGI script</H1>”);
...
print (“</BODY>”);
2. Return a location to user
Location:
3. Return no response
Status: 204 No Response
The web server process can automatically insert information into the header of the response. Unfortunaltly CGI-scripts cannot use this mechanism
Reply Status Line
Format: VERSION CODE REASON
Status Code 3 digits 1xx (Informational) 2xx (Success) 3xx (Redirection) 4xx (Client Error) 5xx (Server Error)
Reason: Human-readable phrase
404 (Not Found)
No such page

15. GET and POST request methods
Most common ways to send data from client to server:
GET request
Retrieves appropriate resource from Web server
Form contents are appended as a querystring to the URL
Limits query to 1024 characters stored in request line
Browsers cache (save on disk) HTML pages
Allows for quick reloading
Cache responses to get request
Do not cache responses to post request
POST request
Updates contents of Web server (posting new messages to forum)
The data is sent as part the message body of the request.
Not part of URL and cannot be seen by user
Has no limit for length of query
Posts data to server-side form handler
Note that the client don’t always need to send data to server to generate a response
Also called HTTP Request types
Other request methods:
PUT - Take my message body and store it as the identified resource
DELETE - Delete the resource
Hur ser ett CGI-program ut?
Ett program som är kopplat via CGI till en websida hanterar data som skickats via GET eller POST från den aktuella sidan
Två sätt att skicka data: GET och POST
GET
Begränsat hur mycket som kan skickas
(Problem med cache?)
POST
sends all the information from the form separately from the URL.
Skickar formulärets data direkt in I webbapplikationen som en dataström med hjälp av <STDIN>
GET vs. POST
GET = slightly more limited, but easier to deal with. Data may get lost or truncated
POST = substantial text entry fields
POST is usually preffered because the amount of information that can be sent is not limited by the size of a URL. The most common method is POST
… but what is the difference? The answer lies within the way information is passed...
Vilken ska användas?
GET ska användas för att fram data, till exempel söka efter ett specifikt namn i ett adressregister
POST ska används för att modifiera data, till exempel lägga till en post i ett adressregister
POST ska även användas när informationen bör döljas för användaren
GET Requests can be stored as bookmarks

16. Ways to call Server-Side Scripts
The URL specifies a script called “program” to be executed Instead of an HTML file.
Sending data directly to a script (using the GET-method)
Invoking can also be done through a link. A hypertext reference can refer to:
An exutable script
<a href=
An exutable script with arguments (using the GET-method)
<a href=
An Active Server Page
<a href=
It is much easier provide user input from an HTML form:
<FORM ACTION=“
Input elements go here
</FORM>
LT 5-5
Flyttas ev till FORMS, GET o POST (se Calgary)
All examples scripts could also be invoked with the POST-method
Other Methods than using forms with GET or POST to access CGI
Can be done through URL
<A HREF=“
Can be done through link
Invoking a CGI program in the cgi-bin directory
The directory that the CGI scripts sit in cannot be specified by you alone - you need the help of whoever runs your HTTP server
Most of Google is implemented in C or C++ for efficiency and can run in either Solaris or Linux
Data of request is sent as name/value pairs
Komplettera ev. med JSP och PHP ev. Phyton
webserver extensions
An exutable program that extends the server
<a href=
A hypertext reference can refer to
(A local file <a href=file:///docs/system.html>
A remote file <a href=
Requesting documents
Must know machine name on which Web server resides
Through local Web servers or remote Web servers
Through domain name or Internet Protocol (IP) address
Local Web server
Resides on users’ machines
Requests documents in two ways
Machine name
localhost
Host name that references local machine

17. Encoding User Input from Forms
HTML-forms are used to provide input to CGI scripts. The <FORM> tag requires two arguments:
ACTION
the URL representing the script which is to receive the form information
METHOD
either GET or POST
represents the way in which the information will get passed to the script
Using METHOD=“GET”.
FORM elements’ names are paired with their contents ie. <input type=“text” size=“9” maxlength=“9” name=“zip”> User inputs 10003, then zip=10003
All such name/value pairs are joined together with an ‘&’
The entire input data string is URL encoded ie. name=Jane+Doe&address=35+W%27+4th+St%27&zip=10003
On the server end the data is placed in the environment variable QUERY_STRING
Kommunikationen mellan webbbläsare och webbserver sker med hjälp av formulär som användaren fyller i och sedan skickar till en webbapplikation för bearbetning
Forms are one of the most popular, interactive features on the web. They enable users to interact with the text and graphics that are displayed on your machine.
when the user submits the form, the information is returned to a server-side script. A script is a short program that is written specifically for each form.
Vad är Forms?
Ett sätt att i HTML skapa sidor som använder inmatning av information från användaren och koppla hantering till program på en server
Vi kan hantera knappar, textfält, listor, mm
Information in the form is forwarded to a script that can process the data
Varför Forms?
HTML är ett språk för att beskriva innehåll på sidor och inte hur det skall hanteras
FORMS är ett sätt att beskriva olika grafiska objekt och koppla hanteringen av användarens inmatning via CGI till program skrivna i konventionella programspråk
GET
Lägger formulärets data till slutet av URL:en i kodat format
Parameter form:
name = value, (Spaces replaced with +)
Name/value pairs separated by & (ampersand)
Space replaced by a ‘+’ sign
Se Calgary eller Cal State Bild
METHOD selects variations in the sending protocol. Tells the form how to send its information back to the script.
<input type=“text”…
type attribute determines input type: A single-line text field
The browser specially encodes the form’s data before passing it to the server. The standard encoding format is “application/x-www-form-url-encoded” Spaces are converted to + sign, non-alphanumerics to %ASCII_hex_value, and line breaks into %0D%0A
Using METHOD=“POST”; we have
Basically the same as METHOD=“GET”
Parameters are encoded as with GET for consistency.
string -> STDIN
length of string -> CONTENT_LENGTH

18. Three ways to pass data to CGI scripts
Environment variables (When the GET method is used in an HTML form)
Data is encoded as part of the URL
Portions of the URL are assigned to the environment variables QUERY_STRING, PATH_INFO, and SCRIPT_NAME:
QUERY_STRING is assigned input_data
PATH_INFO is assigned extrapath/afile
SCRIPT_NAME is assigned cgi-bin/scriptname
Standard input (When the POST method is used)
The data is given in the message body of the HTTP request
Web server forwards message body to the script via the standard input stream
Command–line arguments
For example, to pass arg1 and arg2 to a script:
<a href=
LT 5-14 AL-14
method = ”post” appends form data to the browser request, which contains the protocol (HTTP) and the requsted resource’s URL
Retrieving parameter values.
Determine whether parameters are in QUERY_STRING or on STDIN
Use “split” to break parameter/value pairs.
Use “split” to break parameters from value
Replace “+” with a space.
Replace “%##” with characters (use “pack”)

19. CGI Environment Variables
CGI environment variables are used to pass information about the context of execution. These variables are global, and accessible to all running programs
Programs -> programs
Variables are text strings (name and value pairs)
Can be classified into two major categories
Nonrequest specific
Request specific
Nonrequest-specific environment variables
These variables are set for all requests
SERVER_SOFTWARE The name and version of the information server software answering the request
SERVER_NAME The server's hostname, DNS alias, or IP address
GATEWAY_INTERFACE The revision of the CGI specification to which this server complies.
LT , se även Calgary (komplettera med kolumn med exempel på värden)
Knowing the client’s execution environment allows system administrators to provide client-specific information to generate clinet specific Web pages.
Vidare kan programmet hantera andra omgivningsvariabler för att tex kontrollera om anropande websida "körs" från en bläddrare på en gilltig plattform (vi kan tex se till att endast bläddrare startade på någon av NADAs datorer kan köra CGI-programmet)
Can be accessed by other running programs
Function param is part of Perl CGI module and retrieves values from a form field’s value
(Mastering boken delar upp variablerna I 3 grupper
Server (Non request)
Request
Client)

20. Request-specific environment variables (1)
These variables are set depending on the request being fulfilled by the CGI script:
SERVER_PROTOCOL The name and revision of the information protocol this request came in with. Format: protocol/revision
SERVER_PORT The port number to which the request was sent.
REQUEST_METHOD The method with which the request was made. For HTTP, this is "GET", "POST", etc.
PATH_INFO The extra path information, as given by the client. E.g.
PATH_TRANSLATED the PATH_INFO path translated into an absolute document path on the local system, which takes the path and does any virtual-to-physical mapping to it.
SCRIPT_NAME A the path and the name of the script being executed, as referenced in the URL.
QUERY_STRING The information which follows the ? that referenced this script.
Important request variable: REQUEST_METHOD
’OBS! PATH_INFO Definitionen ovan stämmer ej med Bild 17
PATH_INFO The extra path information, as given by the client. In other words, scripts can be accessed by their virtual pathname, followed by extra information at the end of this path. The extra information is sent as PATH_INFO. This information should be decoded by the server if it comes from a URL before it is passed to the CGI script.
PATH_TRANSLATED The server provides a translated version of PATH_INFO, which takes the path and does any virtual-to-physical mapping to it.
QUERY_STRING has encoded parameters if using GET
QUERY_STRING This is the query information. It should not be decoded in any fashion. This variable should always be set when there is query information, regardless of command line decoding.

21. Request-specific environment variables (2)
REMOTE_HOST The Internet domain name making the request.
REMOTE_ADDR The IP address of the remote host making the request.
AUTH_TYPE If the server supports user authentication, and the script is protects, this is the protocol-specific authentication method used to validate the user.
REMOTE_USER the username that server and script have authenticated.
REMOTE_IDENT the remote user name retrieved by the server using inetd identification (RFC 931),
CONTENT_TYPE For queries which have attached information, such as POST-method, this is the MIME-content type of the data.
CONTENT_LENGTH The length of the content as given by the client.
Important request variable: CONTENT_LENGTH hint: Use the environment variable CONTENT_LENGTH to determine how much data to read
REMOTE_HOST If the server does not have this information, it should set REMOTE_ADDR and leave this unset.
AUTH_TYPE If the server supports user authentication, and the script is protects, this is the protocol-specific authentication method used to validate the user.
REMOTE_USER If the server supports user authentication, and the script is protected, this is the username they have authenticated as.
REMOTE_IDENT If the HTTP server supports RFC 931 identification, then this variable will be set to the remote user name retrieved from the server. Usage of this variable should be limited to logging only.
Also, every item in an HTTP request header is stored in an environment variable for example: HTTP_USER_AGENT
Se core servlets
Accept
Accept-Encoding
Authorization
Connection
Referer
Host
If-modified-since
Se NorthC headers

22. Perl script to display CGI environment variables
#!/usr/bin/perl
2 # Fig : fig27_11.pl
3 # Program to display CGI environment variables. 4
5 use CGI qw( :standard ); 6
7 $dtd =
8 "-//W3C//DTD XHTML 1.0 Transitional//EN\"
\" 10
11 print( header() ); 12
13 print( start_html( { dtd => $dtd,
title => "Environment Variables..." } ) ); 15
The use statement instructs Perl programs to include the contents (e.g., functions) of predefined packages called modules. The import tag :standard imports a predefined set of standard functions.
Fig27_11.pl
Calgary har ett enklare exempel (Dela upp ex på två sidor) el. Byt mot ex att ta emot data fr formulär )
qw places quotes around a list of words
3 # Program to display CGI environment variables.
CGI.pm is a library of routines that simplify the creation and processing of Web forms.
-         handle the extraction of data
-         includes shortcuts which can be used to create common HTML tags
-         Attribute to tags have their standard HTML names and are preceded by a dash.
If you want to create non-form pages these shortcuts are actually more complex than writing your own print statements.
CGI.pm operate as classes and allow the programmer to access their routines through method calls
Methods are accessed by using an arrow 
Module has a name (starting with uppercase)
Examples: MyModule, CGI
Stored in a file with same name with .pm ending
Examples: MyModule.pm, CGI.pm
DTD (or a schema) shows what HTML-version is used. Some parsers can read the DTD/schema and check that the document follows the structure that DTD/schema defines to The DTD shows the DTD in use by the document: XHTML Transitional
11 print( header() );
Instruct the Perl script to print a valid HTTP header, using function header from the CGI library. Prints Content-type::text.html
The start_html function prints the document type definition for this document, as well as several opening XHTML tags (<html>, <head>, <title>, etc., up to the opening <body> tag).

23. Perl script to display CGI environment variables, cont.
16 print( "<table style = \"border: 0; padding: 2;
font-weight: bold\">" ); 18
19 print( Tr( th( "Variable Name" ),
th( "Value" ) ) ); 21
22 print( Tr( td( hr() ), td( hr() ) ) ); 23
24 foreach $variable ( sort( keys( %ENV ) ) ) { 25
print( Tr( td( { style => "background-color: #11bbff" },
$variable ),
td( { style => "font-size: 12pt" },
$ENV{ $variable } ) ) ); 30
print( Tr( td( hr() ), td( hr() ) ) );
32 } 33
34 print( "</table>" );
35 print( end_html() );
The %ENV hash is a built-in table in Perl that contains the names and values of all the environment variables. Function keys returns an unordered array containing all the keys in the %ENV hash. sort orders the array of keys alphabetically. The foreach loop iterates sequentially through the array returned by sort, repeatedly assigning the current key’s value to scalar $variable.
16 Specifies the value for the attribute style. The name of the attribute is specified on the left, followed by its value on the right.
19 print( Tr( th( "Variable Name" ),
th( "Value" ) ) );
Functions Tr and th place their arguments between table row and table header tags, respectively
24 foreach $variable ( sort( keys( %ENV ) ) )
foreach is used to set the value on each loop foreach. Foreach ger en kompaktare kod
%ENV is a table with keys and value column (Rita hashtabell med key och value
%ENV is a special variable containing the current environment
Fr Henriks
foreach $key (sort keys %ENV) {
print "<strong>$key</strong>";
print "$ENV{$key}";
print "<br>" }
print( Tr( td( { style => "background-color: #11bbff" },
$variable ),
td( { style => "font-size: 12pt" },
$ENV{ $variable } ) ) );
Function Tr is called again with the hr and td functions, in order to print a row of horizontal rules within <td> tags.
Hash values are accessed using the syntax $hashName{ keyName }. In this example, each key in hash %ENV is the name of an environment variable name (e.g., HTTP_HOST).
Function end_html returns the closing tags for the page (</body> and </html>).

24. Program Output Prev notes
Specifies the value for the attribute style. The name of the attribute is specified on the left, followed by its value on the right.

25. Introduction to DBI Databases part of distributed applications Driver
Divides work across multiple computers
Retrieves result set and displays results
Driver
Helps programs access databases
Each database can have different syntax
Each database requires its own driver
Interface
Provides uniform access to all database systems
Database interface
Programmatic library for accessing relational database
Using the web to conduct business depends on storing and retrieving and manipulating data from customers.
If you’re handling complex data a relational database is the best solution.
Lägg ev in LT 6-13 o 6-14 showing a three tier model
If the DBMS that you’re using changes (Oracle) then you simply tell the Perl DBI to use a different driver
A Perl driver is available to talk to ODBC the consistent DBMS interface from Microsoft

26. Perl Database Interface
Perl DBI
Enables users to access relational databases from Perl programs
Database independent
Most widely used interface in Perl
Uses handles (Fig )
Object-oriented interfaces
Driver handles, database handles, statement handles
Each connection into the database is identified by a handle whose methods are called by Perl scripts
Perl DBI is an API which provides a library of functions, variables and conventions.
The functionality comes from a driver module which must be specifically developed for the database being used
Till bild:

27. MySQL Pronounced “My Ess Que Ell” Robust and scalable RDBMS
Multiuser, multithreaded server
Performs multiple commands concurrently
Uses SQL to interact with data
Supports various programming languages
C, C++, Java, Python, Perl, PHP, etc
Supports various operating systems
Windows, Linux and Unix
Access multiple databases with single query
There are many types of relational database available – some of them even freely available on the Internet.
Fig:
Perl script using DBI -> MySQL Driver -> MySQL Engine
MySQL Perl DBI lacks commit and drawback

28. The Perl DBI module and the MySQL driver, DBD::mysql are required.
Fig27_19.pl
1 #!/usr/bin/perl
2 # Fig : fig27_19.pl
3 # CGI program that generates a list of authors. 4
5 use CGI qw( :standard );
6 use DBI;
7 use DBD::mysql; 8
9 $dtd =
10 "-//W3C//DTD XHTML 1.0 Transitional//EN\"
\" 12
13 print( header() ); 14
15 print( start_html( { dtd => $dtd,
title => "Authors" } ) ); 17
18 # connect to "books" database, no password needed
19 $databaseHandle = DBI->connect( "DBI:mysql:books",
"root", "", { RaiseError => 1 } ); 21
22 # retrieve the names and IDs of all authors
23 $query = "SELECT FirstName, LastName, AuthorID
FROM Authors ORDER BY LastName"; 25
26 # prepare the query for execution, then execute it
27 # a prepared query can be executed multiple times
28 $statementHandle = $databaseHandle->prepare( $query );
29 $statementHandle->execute(); 30
31 print( h2( "Choose an author:" ) ); 32
33 print( start_form( { action => 'fig27_20.pl' } ) ); 34
35 print( "<select name = \"author\">\n" );
The Perl DBI module and the MySQL driver, DBD::mysql are required.
Connect to the database by calling DBI method connect. If the connection succeeds, function connect returns a database handle that is assigned to $databaseHandle.
# CGI program that generates a list of authors. Byt mot ex att ta emot data fr formulär se XML How to Program
The databasehandle will be used for all database operations
19 $databaseHandle = DBI->connect( "DBI:mysql:books",
"root", "", { RaiseError => 1 } ); Argument ({ RaiseError => 1 })
is used for error checking. If an error occurs when trying to connect to the database, function die is called and passed an error message.(Application can then use to fail gracefully)
Connect ($datasource $username, $password)
The datasource is a colon-separated set of values identifying the driver, database (and host)
Driver is called through DBI::”driver-name:
The handle is an instance of DBI
Note that SQL-statements should not generally be terminated by a semicolon
What is the contents of the table.
The database handle is used to prepare the query (using the method prepare). This method prepares the database driver for a statement, which can be executed multiple times.
Method execute executes the query.

29. Each value is printed as a list option.
Fig27_19.pl 36
37 # drop-down list contains the author and ID number
38 # fetchrow_array returns a single row from the result
39 while = $statementHandle->fetchrow_array() ) {
print( "<option>" );
print( "$row[ 2 ]. $row[ 1 ], $row[ 0 ]" );
print( "</option>" );
43 } 44
45 print( "</select>\n" ); 46
47 print( submit( { value => 'Get Info' } ) );
48 print( end_form(), end_html() ); 49
50 # close the statement and database handles
51 $databaseHandle->disconnect();
52 $statementHandle->finish();
Method fetchrow_array accesses the results of the query. Each call to this function returns the next set of data in the resulting table until there are no data sets left. Each row is returned as an array and assigned
Each value is printed as a list option.
37 # drop-down list contains the author and ID number
# method fetchrow_array returns a single row from the result
fetchrow_array returns next row from the set of rows returned by the database. The row is returned as an array of values.
Connection should be dropped by calling disconnect
Finish is used to show that no more data will be returned from a statement handle.
Detta går vi ej igenom:
Formulär
[send_form.pl]
<form action=”get_form.pl” method=”post”>
<input type=”text” name=”namn”>
<input type=”submit” value=”skicka”>
</form>
Parsing form (query) data in traditional CGI
Read the data one way for GET requests
Chop pairs at & then separate parameter names (left of the ’=’) from parameter values (right of the ’=’)
URL decode values (e.g. ”%7E becomes ”~”)
Need special cases for omitted parameters
[get_form.pl]
# Ta emot formulärdata
Use CGI qw/:standard/;
My $name = param(namn);
Print $name;
Close the database connection (using method disconnect), and specify that the query is finished by calling method finish
Program Output