PERL PROGRAMMERS AND DEVELOPERS

Regarding Todays perl 5+ version

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Usability enhancements

It is now possible to write much more readable Perl code. (How any C-like language can be called readable is still beyond me!)
Simplified grammar

The new grammar is one half the size of the old one. Many of the arbitrary grammar rules have been regularized. The number of reserved words has been cut by two-thirds. Despite this, nearly all old Perl scripts will continue to work the same.

Lexical scoping

Perl variables may now be declared within a lexical scope.
Arbitrarily nested data structures Any scalar value, including any array element, may now contain a reference to any other variable or subroutine.

Modularity and reusability

The Perl library is now defined in terms of modules that can be shared easily among various packages.

Object-oriented programming

A package can function as a class. Dynamic multiple inheritance and virtual methods are supported in a straightforward manner and with very little new syntax. File handles may now be treated as objects.

Embeddability and Extensibility

Perl may now be embedded easily in your C or C++ application and can either call or be called by your routines through a documented interface.

POSIX compliant

A major new module is the POSIX module, which provides access to all available POSIX routines and definitions via object classes, where appropriate.

Package constructors and destructors

The new BEGIN and END blocks provide a means to capture control as a package is being compiled and after the program exits.

Multiple simultaneous BM implementations

A Perl program may now access DBM, NDBM, SDBM, GDBM, and Berkeley DB files from the same script, simultaneously.

Subroutine definitions may be autoloaded

The AUTOLOAD mechanism enables you to define any arbitrary semantics for undefined subroutine calls.

Regular expression enhancements

You can now specify non-greedy quantifiers and performing grouping without creating a back reference.You can write regular expressions with embedded white space and comments for readability. A consistent extensibility mechanism has been added that is upwardly compatible with all old, regular expressions

Capabilities Of Perl

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One of the most common uses of Perl on the Internet is to process form input. Perl is especially adept at this chore because most of that input is textual-Perl's strength.

Mail Processing

Another popular use of Perl is for the automated processing of Internet e-mail. Perl scripts have been used to filter mail based on address or content. Perl scripts have also been written to automate mailing lists.

Automating Web Site Maintenance

Perl can be used to automate the maintenance of Web sites. Because Web pages are little more than text files in a specific format, Perl is particularly adept at processing them. Perl's socket capability can also be used to contact other sites and request information using HTTP. There has even been a Web server written in Perl.In order to check the links on a site, a Perl program must parse the sites pages starting with the main page, extract the URLs, and determine whether these URLs are still active.

Automating File Retrieval

There are several FTP clients written in Perl. Perl can be used to automate file retrieval via FTP. Again, this combines the socket capability of Perl with its text-processing capability.

Language Capabilities

Perl is optimized for text processing and, therefore, is very efficient at many tasks required of system administrators and application developers. Many of the files used in UNIX systems administration are plain text files. Selecting records, processing the selected records, and reporting exceptions are the heart of many tasks performed in UNIX administration.

In the current versions of Perl, the language also includes much additional functionality, making it appropriate for tasks such as processing socket calls, embedding in programs written in C, and maintaining POSIX-compliant systems.

Socket Capability

Perl has the capability to read/write TCP/IP sockets. This gives it the capability to communicate with servers of all types that rely on socket communication. It also enables you to write utility and "robot" programs in the Perl language. For example, Perl's socket capability can be used to write a robot program to automate the checking of a World Wide Web (WWW) site to verify the validity of links on your Web pages. This can be especially useful in keeping a site up-to-date, given the volatility of the Internet in its relative infancy.

Perl Has Built-In Debugging Facilities

The Perl interpreter has a built-in debugger that can help reduce the time it takes to debug applications. The debugger is activated through the use of the -d switch on the command line. In addition, the -w switch provides a complete set of warnings that can be invaluable in debugging Perl scripts.

Extensibility,Perl And C Language

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Extensibility

Much of the growth in Perl as a platform has come by way of the increasing use of libraries (Perl 4) and modules (Perl 5).The arrival of objects in Perl 5 makes structured design methodologies possible for Perl applications. The language has come of age without loosing any of its flexibility or raw power.

It is now fairly easy to add your code by using modules. It is likely that many of the added-on features of Perl such as socket
handling will be dropped from the core of Perl and moved out to modules after a time. So that core remains same and it will act as added features in the form of modules.

Perl And C Language

Perl programs bear a passing resemblance to C programs, perhaps because Perl was written in C, or perhaps because Larry found some of its syntactic conventions handy. But Perl is lot more concise than C.It has a lot in common with C. But Perl handles the internals of data types, memory allocation, and such automatically and seamlessly.

Perl can access C libraries to take advantage of much of the code written for this popular language. Utilities included with Perl distributions
enable you to convert the headers for these C libraries into their Perl equivalents.

Perl 5.0 can be integrated easily into C and C++ applications. Perl can call or be called by routines written in C or C++. The Perl interface is
through a set of perl_call_* functions. The call to C libraries is through the XS language interface.

Availability Of perl

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Perl is free. The full source code and documentation are free to copy, compile, print, and give away. Any programs you write in Perl are yours to do with as you please; there are no royalties to pay and no restrictions on distributing them as far as Perl is concerned.

The GNU General Public License is one way to distribute free software without the danger of someone taking advantage of you. Under this type of license, source code may be distributed freely and used by anybody, but any programs derived using such code must be released under the same type of license. In other words, if you derive any of your source code from GNU-licensed source code, you have to release your source code to anyone who wants it.

This may deprive the original author of a say in the development of his or her own creation. It can also lead to confusion on the part of the end users as it becomes hard to establish which is the definitive version of the package, whether a particular script will work with a given version, and so on.

That's why Perl is released under the terms of the "Artistic" license. This is a variation on the GNU General Public License which says that anyone who releases a package derived from Perl must make it clear that the package is not actually Perl. All modifications must be clearly flagged, executables renamed if necessary, and the original modules distributed along with the modified versions. The effect is that the original author is clearly recognized as the "owner" of the package. The general terms of the GNU General Public License also apply.

This is the Perl language homepage. It provides links to Perl resources. http://www.perl.com/

Where Perl Is Used ?

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Perl is an interpreted language optimized for scanning arbitrary text files, extracting information from these files, and printing reports based on that information. It is also a good language for many system management tasks.

Perl makes it easy to manipulate numbers, text, files, directories,computers, networks, and programs.It also makes it easy to develop,modify, and debug your own programs portably, on any modern operating system.Perl is especially popular with systems programmers
and web developers.Nowadays, Perl is seen by many as the ideal development language for Web server scripts.

Originally designed for text processing, it has grown into a sophisticated, general-purpose programming language with a rich software development environment complete with debuggers, profilers, cross-referencers,compilers, interpreters, libraries, syntax-directed editors, and all the rest of thetrappings of a "real" programming language.

Many programming projects are high level rather than low level. That means that they tend not to involve bit-level manipulations, direct operating system calls. Instead, they focus on reading from files, reformatting the output, and writing it to standard output-for example, a Web browser. With Perl, the programmer does not need to get involved in the details of how file handles and buffers are manipulated, how memory is allocated, and so on.

In a nutshell, that's the secret to rapid development: Write small amounts of powerful code without having to come across consider awkward issues of syntax at every step.Little Perl code goes a long way. In terms of programming languages, that usually means that the code will be difficult to read and painful to write Larry Wall, the author of Perl, says that Perl is functional rather than elegant, This is especially true of the high-level, macro operations typicallyrequired in Web development As it happens, Perl is quite capable of handling some pretty low-level operations, too. It can handle operating system signals and talk to network sockets.

Origin Of Perl

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Back in 1986, Larry Wall found himself working on a task which involved generating reports from a lot of text files with cross references.Larry Wall developed Perl in 1986. He was a systems programmer on a project that was developing multilevel, secure wide area networks. Larry was in charge of an installation consisting of three Vaxes and three Suns on the West Coast of the United States connected over an encrypted serial line (1200 baud!) to a similar configuration on the East Coast of the United States. Larry's primary job was system support "guru." During this stint, he developed several useful UNIX tools such as rn, patch, and warp.

Perl was developed in response to a management requirement for a configuration management and control system for all six Vaxes and all six Suns. As with most management requests, Larry had a month to develop this tool!

Being a UNIX programmer, and because the problem involved manipulating the contents of text files, he started touse awk for the task. But it soon became clear that awk wasn't fitting the job; with no other option for the job, he'd just have to write some code.

Instead of wasting time on utility tool, he invented a new language and wrote an interpreter for it.The new language had an emphasis on system management and text handling. After a few revisions, it could handle regular expressions, signals, and network sockets, too. It became known as Perl and quickly became popular with frustrated, lazy UNIX programmers.

Perl is short for "Practical Extraction and Report Language", although it has also been called a "Pathologically Eclectic Rubbish Lister." There's no point in arguing which one is more correct, because both are endorsed by Larry Wall, Perl's creator and chief architect, implementor, and maintainer

Larry moved on to support research and development and took Perl with him. Perl was becoming a good tool for system administration. Larry borrowed Henry Spencer's regular expression package and modified it for Perl. Then Larry added most of the goodies he and other people wanted and released it on the Internet.