1 CGI (Common Gateway Interface) CmpE 587 Emir Bayraktar Onur Bük

2 Overview What is CGI ? How it works Perl Language Cgi Environment Variables Get & POST Methods Server-Side Includes (SSI)

3 What is CGI ? It stands for Common Gateway Interface It is a way of programming for the web It is a server-side technology It makes web-pages dynamic

4 Basics of CGI CGI can be written with many languages Most popular are PERL and C Our choose is PERL because... PERL is standard on UNIX systems PERL is very easy and robust It also runs on WindowsNT

5 How it works ? CGI combines HTML tags with program statements HTML tags are for appearance and visuality PERL codes are for functionality The result are functional and nice web- pages

6 Before we begin PERL is an interpreted language You write the script and it runs But only if it is error-free A simple text editor is enough No additional software required

7 Let’s begin with the first script We need to know where PERL runs %>whereis perl or %> which perl /usr/bin/perl The first line of our script would be #!/usr/bin/perl As the result must be an HTML code print “Content-type:text/html\n\n”;

8 Default First Script : “HELLO WORLD” #!/usr/bin/perl print “Content-type:text/html\n\n”; print “ HELLO \n”; print “ \n”; print “ HELLO WORLD \n”; print “ \n”;

9 PERL Variables Like many other programming languages, PERL has different kinds of variables SCALAR VARIABLES ==> $scalar ARRAY VARIABLES HASH VARIABLES ==> %hash

10 Scalar Variables A scalar variable stores a scalar value. They have the prefix $. They can contain any kind of data like numbers, characters or a string. $num=5; $name=“John”; You can input data to a scalar variable with $name= ;

11 Array Variables An array stores list of information. They have the The arrays start with the index 0. If you refer to a single element of the array, you use the prefix $ with the index. For $city[0] =“ist” $city[2] =“izmir”

12 Hash Variables Hash variables are a special kind of arrays. They contain paired groups of elements. Each pair consists of a key and data value. They have the prefix %. %pages = ( ”Yahoo" => " ”Mail" => " ”Uni" => " );

13 CGI Environment Variables These are a series of hidden values that the web server sends to every CGI you run. They are stored in a hash called %ENV. Some of them are… DOCUMENT_ROOT:The root directory of your server HTTP_HOST:The hostname of your server REMOTE_ADDR:The IP address of the visitor REMOTE_HOST:The hostname of the visitor SERVER_NAME:Your server's qualified domain name

14 Properties of %ENV The %ENV hash is set for every CGI, and you can use any or all of it as needed. For example, you can write the IP address of the visitor with the command: print “Your IP =$ENV{‘REMOTE_ADDR'}\n"; print “Your Port =$ENV{‘REMOTE_PORT’}\n”; print “Your Browser =$ENV{‘HTTP_USER_AGENT’}\n”;

15 Some examples using %ENV Let’s find the IP address of the visitor... #!usr/bin/perl print “Content-type:text/html\n\n”; print <<Finish IP Your IP address: $ENV{‘REMOTE_ADDR’} Finish

16 GET and POST We use GET and POST in order to send data from an HTML document to a CGI program. GET: The input values are sent as part of the URL, saved in the QUERY_STRING environment variable. POST: Data are sent as input stream to the program

17 A simple example with GET We will write a simple CGI script which takes data input from and sends the data with the ‘QUERY_STRING’. The working part of the code is as follows: #!/usr/bin/perl print “Content-type:text/html\n\n” print <<Finish CMPE587

18 A simple example with GET (cont’d) This page collects info about you Name: Surname: Finish

19 A simple example with GET (cont’d)

20 There are two important results If we look at the %ENV variable we would see that $ENV{‘QUERY_STRING’}= name=Ali+Veli&sname=Yilmaz The second result is that the address bar of the result page would look like

21 How to filter unwanted characters There are some unwanted characters in the string: “=”, “+” and “&”. “+” stands for space and “&” separates input values. name=Ali+Veli&sname=Yilmaz First we have to split “name” and “sname”. Fortunately, PERL has a

22 How to filter unwanted characters (cont’d) We have now an array variable. We use the split command for the second time in order to filter “=“ character. As we have many input values we use such a code: foreach $ran { ($field, $value)= split(/=/,$ran); print “$field = $value\n”;}

23 Advantages and disadvantages of GET It is very simple to collect data and process it. You can make forms very easily. This is an advantage. It is not secure. The data that will be sent is a part of the URL. It can be easily obtained by others.

24 An example with POST POST is another method of sending data but it is much more secure than GET. Data will be sent after encoding. It can also send more data according to GET. Encoding requires decoding and this increases the complexity of the script. The decoding tasks are performed by PERL with some simple commands.

25 Decoding Commands There are two basic decoding commands. These are substitute and translate. The syntax for substitute is: $varia =~ s/pattern/replacement An example clears all: $greeting = “Hello name.\n”; $greeting = ~s/name/Ali/; print $greeting;

26 Decoding Commands The syntax for translate is: $varia =~ tr/searchlist/replacelist The translate command turns every character in the searchlist to its corresponding character in the replacelist The upper&lower case transformation can easily be done with $lower =~ tr/[A-Z]/[a-z] $upper =~ tr/[a-z]/[A-Z]

27 How to decode data streams We have seen how to split a data stream. Now, we have to decode the stream with translate and substitute. $value =~ tr/+/ /; $value =~ s/%([a-fA-F0-9][a-fA-F0- 9])/pack(“C”, hex($1))/eg;

28 How we get POST data read (STDIN, Foreach ($varname,$value)=split(/=/,$pair);, $value =~ tr/+/ /; $value =~ s/%([a-fA-F0-9][a-fA-F0- 9])/pack(“C”, hex($1))/eg; $FORM{$varname}=$value; }

29 Server-Side Includes(SSI) Embedded code section in an HTML document. Dependent on type of server Server parses SSI code executes it sends the results to the client

30 Server-Side Includes (cont’d) How does the server understand that the HTML file contains SSI code? The file extension is converted to shtml or The access rights for the file is 755 (in UNIX environment)

31 SSI Structure Ex:

32 Database Connectivity Uses Perl’s DBI Module Ex (pseudocode): use DBI; $dbh=DBI- >Connect(“dbi:mysql:dbname”,”username”,”pswd”); $sth=$dbh->prepare(“sql query”); $sth.execute; while(($var1,$var2,$var3)=$sth->fetchrow){ use variables $dbh->disconnect }

33 Thank You! Please ask any questions you may have.

34 İyi Bayramlar!