Introduction 2 Perl CGI

8/7/2019 Introduction 2 Perl CGI

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CGI PerlProgramming

CGI PerlProgramming

Dr. Abzetdin ADAMOV


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Overview of Course

Objectives Of The Course

Introduction to CGI

Preparing CGI Programs To Work Calling CGI programs on the client side.

Programming CGI Using PERL

Connecting to and interacting withdatabases using ODBC.

CGI Program Examples


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Courses Objectives

To understand how CGI technology works.

To be able to install CGI programs on the

web servers. To identify the ways used to connect client

browsers to CGI Programs

To be able to write CGI programs in PERL To be able to connect to a database and

to run SQL commands.


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Introduction to CGI

CGI stands forCommon GatewayInterface.

CGI is a standard programming interfaceto Web servers that gives us a way tomake our sites dynamic and interactive.

CGI is not a programming language. It is

just a set of standards (protocols.) CGI can be implemented in an interpreted

language such as PERL or in a compiledlanguage such as C.


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Introduction to CGI(continued)

CGI programs work as follows:

STEP 1 (On the client side): Get

Information from the user (using HTMLforms, SSI, Java Applet, ,etc).

STEP 2 (On the server side): Process thedata, connect to DATABASE, search forPATTERNS, ,etc.

STEP 3 (On the server side): Send theresult of computation back to the client.


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Preparing CGI for work

The steps involved in preparing a CGI program for work.

1. Contact your Web host to find out where you shouldput your CGI programs on the server. Usually it will bea directory on the server named cgi-bin.

2. Set up the access permission of directory cgi-binusing the following UNIX command:

chmod 755 cgi-bin/

3. Set up the access permission of the CGI programusing the following UNIX command:chmod 755 cgi-program

4. Test your CGI program from the server command lineto make sure it works perfectly before publishing it.


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Calling CGI Programs On The

Client Side

(Using HTML Forms)

. . .

Two HTTP methods are available:

GET

POST

The CGI program will be invoked every time you thebutton SUBMIT is clicked.

See HTMLFormDemo.html


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Calling CGI programs on the

client side(Using SSI extensions)

SSI stands forServerSide Includes.

Two ways to invoke a cgi program here:

For SSI to be used , your Web server must be alreadyconfigured to accept SSI extensions.

Usually html files that contain SSI extensions are given theextension .shtm or .shtml.


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CGI Programming in PERL

PERL stands forPractical Extraction ReportLanguage.

PERL

Is an interpreted language. Runs on multiple platforms:Windows, Unix, Mac, ,

etc.

Is a scripting language.

Is a typeless language. Has some aspects similar to C language.

Could be as procedural as you want it to be.

Could be as object-oriented as you want it to be(PERL 5).


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Introduction to PERL

PERL can be downloaded from:

http://www.perl.com/pub/a/language/info/software.html

To run PERL programs:

On UNIX, type the command from UNIX shell:

perl perl_prog.pl

On Windows, type the command from DOS prompt:

perl perl_prog.pl

PERL is a case-sensitive language just like C or Java.

#sign is used for comments in PERL Example:

#!/usr/bin/perl

# This program is to . . .


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Programming Standards

The following coding standards should be followed:

Start the program with a header comment giving info aboutthe PERL path, programmer, copyrights, last modifieddate, and description.

Example:#!/usr/bin/perl

######################################

# Abzetdin Z. Adamov

# Copyrights 2005

# All rights reserved.

#

# Last modified 05/02/2007

# This program is to . . .

######################################


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Programming Standards(Continued)

Use three-line-comment style. Example:#

# Incrementing variable $count.

#$count++;

Use meaningful names for variables orsubroutines. Capitalize every word except the

first one. Example:$myBuffer=1;sub printThankYouMessage(){

}


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Programming Standards(Continued)

For file handlers such as STDIN, STDOUT useall-cap identifiers.

Use three-space indentation. Example:

## comment here

#

$buffer = '';

foreach $field (@array1){foreach $value (@array2){

$buffer .= "$field: $value\n";

}

}


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PERL Data Types

PERL has three built-in data types: scalars,arrays of scalars, and associative arrays ofscalars, known as "hashes".

Scalar Variables A scalar may contain one single value in any of three

different flavors: a number, a string, or a reference.

Scalar values are always named with '$ at thebeginning, even when referring to a scalar that is partof an array or a hash. Examples:$day #A simple scalar value "day"

$day[28] #the 29th element of @day

$day{'Feb'} #The 'Feb' value from %day


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PERL Data Type(Continued)

Array Variables

An array is basically a way to store a whole bunch ofscalar values under one name.

An array name begins with an "@" symbol. Examples:

@arrayName = ("element1", "element2");

@browser = ("NS", "IE", "Opera");

@one_two_thre = (1, 2, 3);

To access a single element is an array, use a $+array

name+[ + index+]. Array indexing starts form zero.Examples:

$arrayName[0] # the first element of the

# array

$browser[1] # This will return IE.


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PERL Data Type(Continued)

Associative Arrays Hashes Associative arrays are created with a set of

key/value pairs. A key is a text string of your choice

that will help you remember the value later. A hash name begins with % sign. Examples:%hashName = ('key1', 'value1', 'key2','value2');

%ourFriends = ('best', 'Don', 'good','Robert', 'worst', 'Joe');

To access an element, use $+hash name+{+key+}.Examples:$hashName{key1} #This will return value1

$ourFriends{'good'} #This will return

#Robert


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Operators

PERL uses: Arithmetic operations: +, -, *, /, %,**.

Relational operations: , =, ==.

String Operations: ., x, eq, ne, lt, gt, le, ge. Assignment Operators: =, +=, -+, *=, /=, .=.

Increment/decrement operators: ++, --.

Boolean operations: &&, ||, !.

Quotation marks: character string with variable interpolation. character string without variable interpolation.

` system commands stings with variable interpolation.

qq|| character string with variable interpolation.


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Control Structures

If /else control structure looks like:if(condition){

If body

}

else{Else body

}

Example:if ($gas_money < 10) {

print "You dont have enough money!";

}

else {

print "You have enough money.";

}


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Control Structures(Continued)

For loop has the following C-based formula:for (initialize;condition; increment){

code to repeat

}ForExample:

for ($count=1; $count


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Control Structures(Continued)

WhileExample:

$count=1;

while ($count < 11){

print "$count\n"; $count++;

}

foreach has the following formula:foreach variable_name (array_name){

code to repeat

}

ForeachExample:

foreach $item(@inventory){

print $item\n;

}


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Dealing With Files In PERL

Reading Files: STEP 1: Open the file for reading:

open(DFH, data.txt") || die(Cant Open file);

STEP 2: Read the data from the file:

@rawData = ;

STEP 3: Close the file:close(DFH);


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Dealing With Files In PERL(Continued)

Writing to files: STEP 1: Open the file for writing:

open(DFH, >data.txt") || die(Cannot Open file);

STEP 2: Write data to the file:

print DFH New Data;



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Dealing With Files In PERL(Continued)

Appending Files: STEP 1: Open the file for appending:

open(DFH, >>data.txt") || die(Cannot Open file);

STEP 2: Write data at the end of the file:

print DFH Another data line;



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PERL Subroutines

A subroutine is a named group of statementsthat does a specific job and can be called overand over. Subroutines are very important forsoftware reuse.

The formula of creating subroutines in PERL issub subName(){

group of statements

}

TO call a subroutines as follows:subName(arg1, arg2, arg3, );

PERL pass the arguments to subroutines in anarray named

@_


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Useful Built-in Functions

The chop function is used to "chop off" the lastcharacter of a string variableExample: chop(Hii); #return Hi

The length function simply gives you back thenumber of characters in a string variable.Example: length(Hello); #return 5

The substring function is a way to get a portion of

a string value, rather than using the entire value.Example:

$str = substr(Cold, 1, 3); #return old


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Useful Built-in Functions(Continued)

The split function separates a string expressioninto a list. Example:my (@pairs) = split(/&/, $buffer);

The translate(tr) function exchanges eachoccurrence of a character in the search stringwith its matching character in the replacementstring. Example: $value =~ tr/+/ /;

The substitute(s///) function searched the searchstring for the input pattern and replaces it withthe replacement pattern. Example:$searchString =~ s/OPattern/NPattern/g;


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Regular Expressions

PERL has three primary functions that useregular expressions: split, substitute(s///) andpattern-match(m//).

These functions are used to extract the datasent by the client before processing it on theserver side.

Example:

($name, $value) = split(/=/,$pair);$value =~ tr/+/ /;

$value =~ s/%([a-fA-F0-9][a-fA-F0-9])/pack("C",hex($1))/eg;

See the handout titled Regular Expressions.


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Environment Variable

Associative array %ENV is used to carry on the

information coming from the client. PERL gives you

an access to this variable. Therefore you start your

CGI program by extracting this information.

Name What it Gets

CONTENT_LENGTH Number of characters submitted from a

POST commandHTTP_USER_AGENT Type of Browser viewer is using.

QUERY_STRING String in URL after the ? character

REMOTE_ADDR Remote user's IP address


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Database Connection In

PERL

You can use two ways to access a databasefrom a PERL program.

Using DBI Using ODBC

Using ODBC is currently supported by everymajor software company in the world.

In this tutorial, MS Access will be used. Yet itwill still be the same with ODBC whether youconnect to MSACESS, DB2, or any otherdatabase.


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Database Connection In PERL

(Continued)

Steps of connecting to a database. STEP 1: Identify the database drivers you

have on you system. STEP 2: Create your database created.

STEP 3: Create DSN (Date Source Name)for your database. You can do that

graphically form the CONTROL PANNEL,or through programming .

STEP 4: Connect to the database usingthe Win32::ODBC module.


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CGI Program Examples

PROGRAM 1:Suppose you have a database. You want to connect

to it. What we should do is to create first a DSN.Then you need to connect to the database. Once

you are connected, you can make query to thedatabase using SQL statement. So lets do that.

PROGRAM 2:Suppose that we have a couple of listservs that we

want our user to be able to subscribe orunsubscribe to. We want to create first a GUIinterface (Using HTML form) that will take the theuser information and send it back to the cgiprogram which in turn will send subscription or un-subscription to the listserv on behalf of the user.

Introduction 2 Perl CGI

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