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2. Perl Programming Environment

2.1 Brief History of Perl (Practical Extraction Report Language)

Invented by Larry Wall for use by UNIX system administrators to perform routine system administration tasks, collect statistics on system performance, and generate periodic status reports
Not invented to be used on the Web
Primary Web development tool for the past 11 years (1989)
Back to mid'90s UNIX Administrators and Network Servers used Perl to manage UNIX-based Web server (Webmaster)
Perl is now a scripting language widely used for system administration and programming on the World Wide Web.

2.2 Perl Applications for Now

Implemented for more than dozen different operating systems: UNIX, Macintosh, MS Windows, IBM OS/390 mainframes, etc
CGI scripting and Web-based applications
Managing server log files
Load-banlancing server farms
Monitoring servers for performance problems
Automating backup procedures
Generating periodic report on Web server usage

2.3 Perl CGI Script Libraries

CGI.pm library module: a standardized routines for parsing form input and generate HTML pages
DBI library module: routines for accessing relational databases
LWP library module: routines for connecting to Web and FTP servers

2.4 Perl Limitations

Criticized for poor performance
Resource hog: use lots of memory
Perl CGI scripts are not CPU-bound but I/O-bound
High startup cost (latency): a server-side script may takes a second to load before it begins running and new Web requests are coming several times a second. This is the problem.

Helps for Improving the Slow Start Problem

Mod_perl Apache module: a Perl interpreter embedded inside the Apache Web server. It eliminates the start-up costs of Perl CGI scripts (about 10 fold increase in CGI execution speed)
PerlEx: a similar commercial product, from ActiveState, for Microsoft IIS, Netscape Enterprise Server, and Microsoft Personal Web server

2.5 Perl Programming Environment

Getting and Installing Perl

Perl Information Web Pages

O'Relly's Perl Home page

www.perl.com

Comprehensive Perl Archive network (CPAN)

www.cpan.org

Activestates

www.activestate.com

Larry Wall's Third "State of the Onion" Address

www.perl/com/pub/1999/08/onion/talk1.html

Perl for Windows Environment

Including in Widnows NT resource kit
A full-fledged ActiveX script language
Can be used as the scripting language in server-side Active Server Pages (ASP)
Client-side script (like JavaScript or VBScript functions)

Other New Features for Perl in the Windows Environment

Support for fork() on Windows platforms -- launch a subprocess in the background; for parallelizing time-consuming operations and networking applications
Unicode and locale support
Multithreading allows a single Perl script process to run multiple simultaneous threads of execution
Regular expression enhancements
Perl compiler

Check if you have a Perl:

Perl.exe -- The Perl Interpreter in the 'bin" directory

C:\Perl\bin>perl -v

This is perl, version 5.005_03 built for MSWin32-x86-object

(with 1 registered patch, see perl -V for more detail)

Binary build 522 provided by ActiveState Tool Corp. http://www.ActiveState.com

Built 09:52:28 Nov 2 1999

Perl may be copied only under the terms of either the Artistic License or the

GNU General Public License, which may be found in the Perl 5.0 source kit.

Complete documentation for Perl, including FAQ lists, should be found on

this system using `man perl' or `perldoc perl'. If you have access to the

Internet, point your browser at http://www.perl.com/, the Perl Home Page.

Editor for Creating Perl Programs

Text editors

emac -- UNIX

vi -- UNIX

pico -- LINUX

edit -- Windows

notepad -- Windows

filename.pl -- The file extension for Perl program for associated with the Perl Interpreter

CGI Scripts will be created directly on the UNIX or LINUX server if you are using vi, emac, or pico editor for creating scripts.

If you use MAC or PC to write your scripts and the Web server is at a remote location, you would need to do the following

Use FTP to upload file to script directories
Telnet to the UNIX server to change the permissions for files and scripts. It is generally set up in the way so that the owner can read and write to it, and others can just read it. For scripts, execution should be permitted.

2.6 Create and Test Perl Programs

Create a testing.pl script for Windows environment

1. Start --> Programs --> Accessories --> Notepad

2. Enter the three lines as shown below:

#!/usr/bin/perl -w

#testing.pl

print("My first Perl Program\n");

print("Hello!\n");

3. Save the file as "testing.pl" and place it in bin directory

4. Run the testing.pl program

C:\Perl\bin>perl testing.pl

My first Perl Program

Hello!

5. For UNIX environment

Change the file into executable:

$chmod +x testing.pl

Run the program under the command line

$testing

Exercise

1. Use Notepad to enter the following Perl statements

#printex.pl

print (1,2,3,4,5);

print "\n";

print (1..15);

print "\n";

print (a..z);

2. Save it as printex.pl

3. Run the program to verify the result

C:\ActivePerl522\bin>perl printex.pl

12345

123456789101112131415

abcdefghijklmnopqrstuvwxyz

Running Perl for LINUX

· Login to LINUX machine: telnet 149.164.36.10

· Check the version of the Perl Interpreter

[plin@ecetlin plin]$ perl -v

This is perl, version 5.005_03 built for i386-linux

Perl may be copied only under the terms of either the Artistic License or the

GNU General Public License, which may be found in the Perl 5.0 source kit.

Complete documentation for Perl, including FAQ lists, should be found on

this system using `man perl' or `perldoc perl'. If you have access to the

Internet, point your browser at http://www.perl.com/, the Perl Home Page.

· Start PICO editor; enter the first program as shown below; then save the program as "test1.pl" by entering Ctrl W to write to a file and enter the file name: pico test1.pl

· Run the program

[plin@ecetlin plin]$ perl test1.pl

My first Perl Program

Hello!

· View all files in the working directory using ls -al command

[plin@ecetlin plin]$ ls -al

total 56

drwx------ 3 plin plin 4096 Nov 15 14:33 .

drwxr-xr-x 28 root root 4096 Nov 13 15:01 ..

-rw------- 1 plin plin 447 Oct 2 10:41 .bash_history

-rw-r--r-- 1 plin plin 24 Sep 28 09:56 .bash_logout

-rw-r--r-- 1 plin plin 230 Sep 28 09:56 .bash_profile

-rw-r--r-- 1 plin plin 124 Sep 28 09:56 .bashrc

-rw-r--r-- 1 plin plin 3394 Sep 28 09:56 .screenrc

-rw-rw-r-- 1 plin plin 29 Sep 30 12:46 date.txt

drwxrwxr-x 2 plin plin 4096 Sep 30 13:10 localsite

-rw-rw-r-- 1 plin plin 27 Sep 30 12:50 names

-rw-rw-r-- 1 plin plin 746 Sep 30 13:06 pingfile.txt

-rw-rw-r-- 1 plin plin 27 Sep 30 12:59 reversenames

-rw-rw-r-- 1 plin plin 27 Sep 30 12:56 sortnames

-rw-rw-r-- 1 plin plin 85 Nov 15 14:33 test1.pl

[plin@ecetlin plin]$

· Recognizing file permissions

Three levels of permissions associated with three classes of user groups:

User (u) - the owner of the file or directory. The owner's name can be seen

in the display.

Group (g) - the group that owns the file.

Others (o) - Any users

Three levels of permissions:

r - Read the file or directory

w - Write the file or directory

x - Execute the file

· Change the file mode for "read", "write", and "execute"

Note that you must have at least "read" and "execute" permission to run a Perl program.

Add execute permission for the owner (or user) of test1.pl

ls -l test1.pl

-rw-rw-r-- 1 plin plin 83 Nov 15 14:56 test1.pl

chmod u+x test1.pl

ls -l test1.pl

-rwxrw-r-- 1 plin plin 85 Nov 15 14:33 test1.pl

Add permission for both the group and other classes

chmod go+rx test1.pl

ls -l test1.pl

-rwxr-xr-x 1 plin plin 85 Nov 15 14:33 test1.pl

2.7 LINUX/UNIX Security Mechanism

File security:

File attributes:

.Directory or regular file

.Owner read, write, execute

.Group read, write, execute

.Users read, write, execute

Changing file permissions control access to files, directories, and devices (shell commands)

$chmod .... change permissions

$chown .... change ownership

$chgrp .... change group

chmod 755 thisFile (for CGI scripts that needs to be executed)
chmod 644 otherFile (for non-executable files such as log files, configuration files, libraries, and others)

Password security: a password scheme prevents unauthorized users from logging in.

$cat /etc/passwd

-To change password:

$passwd