Perl was developed in 1986 by Larry Walls to create reports for a company he worked for. Perl was not really designed for the web ,insomuch that it was found that the two sort of went togeather like coffee and donuts. It is said that PERL stands for Practical Extraction and Report Language.

Since its creation Perl has become a very popular programming language among web developers .It has evolved into a powerful full featured programming language though only parts of this robust language are used for web development.

You will be hard pressed to find another web development tool that has more support,public code,and followers as Perl does. It has matured and been added to and updated along the way to become the popular language its become.

Its an easy to learn language and you will find few arguments among site designers about the benefits of adding it to your skills as a web site designer.

Perl is used for a wide variety of things but this tutorial will focus only on its popular use as a tool to make web sites interactive.

Perl scripts can process forms,create guestbooks,web-based bulletin boards,count page hits,and a lot more.

Perl is well suited to Web-related tasks for three reasons.

1. It is a powerful text manipulation tool.
2. Perl is easily ported,(moved from one platform to another).
3. Perl is a friendly easy to use programming language.

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Perl and HTML make good partners.

HTML allows you to create links and forms that access or activate your Perl scripts.

Perl allows you to generate HTML code in the background of your web pages which will display the result of the script to visitors at your site. Pretty cool , huh?

Examples will follow.

If you need to review HTML visit this link. HTML Primer

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Often computer languages are compared to human languages. The similarities stem from the communicating syntax elements of each.

A typical written sentence contains various syntax elements as does a line of computer instruction. A computer has its "nouns" (variables),"verbs"(commands),and "objects"(operands and arguments).

A computer program is a series of line statements that instruct the cpu to perform a certain function.The program lines can instruct the computer to perform an action, or simply provide information related to the program.

The elements of each statement are the functions and expressions.Again if you compared the computer statement to a human language ,functions would be verbs, and expressions would be complex clauses,and nouns would be variables.

Each statement in Perl ends with a semicolon,not a period.

A working knowledge of human language grammar isnt neccesary to learn programming,but if you are familar with the grammar of human language then the comparison is helpful.

Information is provided to a computer program in the form of data. Text,images,and instructions acted upon are all code data that the computer understands,namely ones and zeroes at the processor level.

Programs hold this data for the computer in variables.Variables are places in memory (addresses) but you need not worry about how the computer decides where to store variable data. You merely specify a variable name within the program to represent or hold the value of some information until the computer needs to access it from within the program.

In a nutshell,variables represent numbers,bits of text,words,expressions,and maybe even other variables.

In Perl there are three types of variables.

Scalars:   Scalar variables hold single values.Any value held in a scalar variable is considered to be a single,discreet unit.The scalar variable is indenified by the $ (dollar sign) in front of the variable name.

$scalar=1

This declares a scalar variable named scalar and assigns the value 1 to it.

Lists:    Also called Array variables,list variables hold multiple values. A single unit of data,(an item) in a list variable is called a list element.

Lists are idenified by the @ sign in front of the variable name. Scalars and Lists are related variables in that list variables contain scalar variables.

Each individual item in a list variable is a scalar variable. You can access the single elements (scalars) within a list by referring to it as a scalar and referencing it by its index number that corresponds to its position in the list.

Example: Let us say we have a list variable called @list and the third element can be idenified as $list[2].The third element is designated as 2 because pc's typically start counting at 0. Therefore 0=the first element ; 1= second element,2=third element, and so on.

Elements within a hash are grouped in pairs. Each pair contains a "key" and a "value".

Values are accessed by referring to their associated key.

%hash= [key1, value1], [key2, value2], [key3, value3]

The key is usually the idenifier and any [value] can be extracted from the hash by referring to its key.

so the value of:

$hash[key2]

would be value2.

A more practical hash might look like this.

%address= (
	   "number" => "2135",
	   "street" => "Elm St.",
	   "City"   => "Cleveland",
	   "State"  => "Ohio",
	)

The symbol => is a convention used in hash data to make the key/value pairs easier to see.It is synomynous with the comma.

To extract the city from this hash you refer to it as

$hash{"city"}

this will represent the value Cleveland.

Notice that each element of a hash is a scalar and is referred to it with the dollar sign, just as the list variable.

Operators    Operators perform or describe some kind of relationship between two things. Some common operators used in programming are the mathematical operators.+, -, *, /, . There are more matematical operators then these basic ones but thats for a later section. Besides mathematical operators there are comparison operators such as = and +=,and increment and decrement operators such as ++ and --.

One typical use of operators is to create or check a condition and have the program perform some operation if the condition matches or doesnt match some predetermined conditions.

An easy condition for example is to compare two numbers to see if they are equal or not equal,or if one is bigger or smaller than the other.This comparision will return either a true or false value.

Text strings can be compared for equality as well . Search tools and your find file programs use such operators to find string matches.

More detail about operators will be introduced in the Conditional and Loops section.

Functions    Functions are the heart and soul of programming. Functions are like operators with names,that perform some kind of operation on the data.They are named,case-sensitive,and always in lowercase letters.Generally they perform more complicated operations on the data then operators.

An example of a Perl function is a print function that sends specified data to the specified output ,which may be a printer or file.

Some functions work on arrays,some on hashes or scalars. Others may work differently depending on where you use them,or what you use them on.

Handles    Handles are special keywords that help identify "something" as a target for certain functions.A file handle is the most common type of handle. It is a label that is linked to a filename. The label is referred to when operations such as opening,closing,reading and writing need to be performed on the file. Handles for directories can also be created for databases and network connections.

Program Grammar     

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