Internet / Intranet Spring 2000

1
Internet / IntranetSpring 2000

• Class 8
• Perl / CGI Scripting

2
Class 8 Agenda

• Homework Discussion Milestone 3
• Presentations
• CGI Scripting
• Perl
• Telnet / UNIX
• Lab Work
• Telnet
• Basic UNIX
• Perl

3
CGI / Scripting

• Scripts are Programs Run By the Server
• CGI Common Gateway Interface
• Methodology For Server/Script Communication
• Can Be Written in Any Language Supported By the
  Server
• UNIX Origins
• PERL is Most Common
• Script Output is Returned to the Browser
• Alternative Methodologies Exist
• CGI is the Most Portable
• PERL Practical Extraction and Reporting
  Language
• UNIX Based Scripting Language
• Ported to Multiple Platforms
• How Does Browser Know to Execute a Program?
• Program is in a Script Directory
• Typically cgi-bin (Apache)
• Or By Extension (e.g. .pl, .cgi)
• Scripts Must Have Executable Permissions

4
Scripting Features

• Scripts Can Have Input Parameters
• Passed as Part of URL ? Argument (Query String)
• Special Characters Passed as Ascii Hex Values
• Name/Value Pairs Separated by
• Variable
• Passed in HTTP Header
• Name/Value Pairs
• Method Post
• HTML Forms
• Passed in Cookies
• Netscape Origins, Now Widely Adopted
• Name/Value Pairs Associated With a URL
• Stored on Client Computer
• Users May Turn off Cookies
• Scripts Must Be Aware of How Parameters are Being
  Passed
• Different Methodology to Access Each Method
• Parameters Also Used to Maintain State
  Information
• Help Track a Session

5
Scripting Issues

• Security Concerns
• No Limits on What CGI Scripts May Access
• Potential to Execute Any System Command
• Hacker Can Cause Serious and Unforeseen Problems
• Potential to Affect More Than Just Your Web Site
• Many ISPs Limit CGI Capabilities
• Performance Concerns
• CGI Scripts are Run as a Standalone Process
• E.g. Interpreter is Loaded and Initialized Each
  Time
• Alternative to Posting Forms
• Mailto Option

6
Perl

• Why Should I Learn Perl?
• S/W Engineers Need to Be Adept at Picking Up New
  Languages
• Need a Comfort Level of Expertise
• Ability to Write Basic Code
• Ability to View/Modify Existing Code
• Ability to Learn More as Needed
• Develop Reference Library
• Develop Guru Network
• Large Public Archives of Perl Scripts
• Perl Basics
• Interpreted
• Originally Used Primarily By UNIX Sys-Admins
• Public Domain
• The preferred language for CGI Scripts
• PERL is Relatively Portable
• Activestate ActivePerl (Windows / IIS)
• UNIX specific scripts dominate (Uses UNIX O/S
  Commands)

7
Perl 101

• C-like
• Lines end with
• Syntax of Print statement is very similar
• Pointers and indirection
• VB-like
• Untyped (except for arrays)
• Associative arrays
• UNIX-like
• Tricks
• e.g. a ltgt retrieves a line of input from stdin
• support for regular expressions
• doublequotes vs. singlequotes
• all examples must contain foo
• Perl-Like
• Variables begin with
• Comments begin with
• Subroutines Begin with
• Associative Arrays Begin with

8
Perl 102

• Powerful Features
• Can run command line commands on O/S (system,
  xxx)
• Can create code on the fly (eval)
• Subroutine Libraries
• Powerful Features Make it a Target of Hackers
• Print is the Most Important Command
• Generate HTML Using Print Statements
• print text to print \n
• Dont forget carriage returns \n
• First Line ! /usr/local/bin/perl
• Output has Mime content-type as first line, blank
  line
• print Content-type text/html \n\n

9
A Simple Perl Example

• ! /usr/local/bin/perl
• First Perl
• mynameEvan
• print ltltEND
• Content-type text/html
• ltHTMLgt
• ltHEADgt
• ltTITLEgt
• lt/TITLEgt
• lt/HEADgt
• ltBODYgt
• END
• print ltH1gtThis is myname s Test Perl
  Script.lt/H1gt\n
• print ltH2gtHello Worldlt/H2gt\n
• print lt/BODYgt\n
• print lt/HTMLgt\n

10
Class Exercise First Perl

• Save This Locally as perl1.pl
• Open a Command Prompt
• perl.exe perl1.pl
• Once You Are Satisfied With the HTML Produced
• Upload This via FTP to public_html/cgi-bin in
  your ShoreNet Account
• Remember to Transfer this In ASCII Mode!
• Give the Script Execute Permissions For All
• Right Button Click / chmod in WS_FTP
• http//shell3.shore.net/brinetxx/cgi-bin/perl1.pl
  

11
Advanced Exercise

• Create a Script Like the One in Stein p.481
• Typo for each should be foreach
• Put it On Your Web Site
• Remember to Give the Script the Appropriate
  Permissions
• OPTIONAL Homework Install a Perl Interpreter On
  Your Local Machine
• Read Stein Chapter 9. Skim Chapter 8.

12
Telnet

• Telnet is a Remote Login Protocol
• Terminal Emulation
• All Processing Occurs on Host
• Command Line Interface
• Port 23
• Used Extensively for UNIX Machines / Multiuser
  Systems
• Why Do We Care?
• Remote Administration of Web Site
• Configuring Web Servers, Setting Permissions

13
Sample Telnet Session

• telnet world.std.com
• Trying 192.74.137.5...
• Connected to world.std.com.
• Escape character is ''.
•  
• UNIX System V.4 (world)
•  
• login evan
• Password xxxxx
• Last login Sun Jan 23 160336 from
  fxtc2-c.std.com
• Welcome to The World! A 24 x 250MHZ CPU 2.5GB
  SGI Challenge XL
• world

DNS Resolves the Name to an IP Address
Found the Telnet Server at This IP Address
Host Information
Login Successful
UNIX Command Prompt
14
UNIX - Background

• UNIX Developed at ATT Bell Labs 1969
• Multi-User / Multi-Tasking
• Many Other Proprietary Operating Systems Existed
• Schools Adopted UNIX as Teaching Environment
• Schools Made Significant Additions and Changes
• Standardization Efforts
• Culture of Sharing / Helping / Working Together
• Free Software Foundation, etc.
• Put Source-Code in Public Domain
• Many Other Free Add-Ons / Extensions
• LINUX
• UNIX Expects Technical Competence

15
UNIX File Structure

• Forward Slashes (/) to Separate Filenames,
  Directories
• Case Sensitive File Names
• Windows is Not
• No Limit on Filename Size / Extensions
• Extensions are by Convention
• Root is /
• User Home Directory is /
• Symbolic Links / Aliases
• Directories Can Be Spread Over Multiple Drives
• Can Create Non-Hierarchical Structure
• File Permissions
• Read, Write, Execute
• Separate Permissions for Owner, Group, All
• Directories are Special Cases of Files
• Execute Permissions Able to Browse Directory

16
Common Basic UNIX Commands

• pwd List the current working directory
• More filename List the Contents of a File
• ls Lists the files in a directory
• ls l
• Permissions drwxrwxrwx
• d If this is a directory
• r,w,x Read, Write, Execute
• Owner, Group, Public
• Owner, Filesize, Timestamp, Filename
• cd change directory
• cd /
• Change to Your Root Directory
• chmod
• Changes Permissions
• Dont Use This Command Until Youre Sure About It
• Can Open Up Serious Security Holes

17
More Unix Commands

• man command
• UNIX help
• e.g. man ls
• cat filename
• List a file
• command more
• All Output can be piped to Display one Screen
  at a Time
• e.g. cat filename more
• Carriage return next page
• q quit
• cp path1 path2
• Copy a File
• mv path1 path2
• Move a File. Useful for Renaming a file

18
The UNIX chmod Command

• UNIX Mode
• chmod abc filename
• Where a,b,c are digits from 0 to 7 (Bit Mask)
• 4 Read, 2 Write, 1 Execute
• a owner, b group, c- others
• e.g. chmod 711 myscript.cgi
• Sets permissions on file myscript.cgi so that
• It is readable, writable, and executable by owner
• It is executable by all others.
• An Easier Way
• chmod urwx,gx,ox
• u owner (user), g group, o other (Not
  Owner!)
• r read, w write, x execute

19
A Caveat

• UNIX Culture Developer Oriented
• Read Access Often Given For Non-Confidential
  Files
• User Responsibility to Not Abuse It
• Be Respectful When Not in Your User Directory

20
Lab Work Telnet

• From a command prompt type telnet
• Connect/Remote System
• Host Name users.shore.net
• Login brinetxx Your Shorenet Login
• Password Your Shorenet password
• ls l
• cd public_html
• ls l
• cd bin
• chmod perl1.pl 600
• Try to access the Script Now
• chmod perl1.pl 755
• ls -l
• cd /
• ls l
• logout

21
Reference Material

• CGI / PERL
• Stein Chapter 9
• http//www.activestate.com/ActivePerl
• Freeware ActivePerl Interpreter For Microsoft
  Platforms
• http//www.shore.net/techtalk/referenceold/cgi.htm
  l
• ShoreNets CGI Reference Page
• http//www.webdeveloper.com/cgi-perl
• CGI/Perl Portal
• http//agora.leeds.ac.uk/Perl/start.html
• A Perl tutorial
• http//worldwidemart.com/scripts/
• Free CGI Scripts (Matts Script Archive)

22
Processing Forms The Server Side

• Target of Forms is Usually a CGI Script
• Script Requirements
• 1. Parse the Data
• 2. Process the Data
• 3. Return Data to the User
• Raw HTML or Another Form
• Data Flow Options
• Each Script Handles a Specific Form
• Form in Plain HTML
• Script in Perl
• One Script Handles Multiple Forms
• Selects Action Based on Data Passed In
• All in Perl

23
Scripting Parsing Data

• GET vs. PUT
• Each Requires Different Logic
• Parsing is Not Trivial
• All Parameters Passed in On One Line
• Each Name/Value Pair Separated by
• Name Separated From Value by
• Special Character Encoding Complicates It
• E.g. Value May Contain ,
• Error Handling
• Typically Use a Library to Parse Data
• Public Domain
• Cgi.pm Perl5 Object Oriented
• Used by Stein
• Cgi-lib.pl Basic Perl
• Used by Schapiro
• Others

24
CGI-LIB

• http//cgi-lib.berkeley.edu/
• Using This Library in Perl
• Download Library From Website
• Version 2.18 Latest Version
• More Robust
• Supports Saving File Uploads as Files
• Version 1.14 Easier to Understand
• Use This Version to Understand cgi-lib Code
• Install it in cgi-bin Directory
• Perl Code
• require (cgi-lib.pl)
• ReadParse()
• More Perl Info
• require Includes Another File
• varname Associative Arrays
• Use Braces to Index, prefix
• e.g. varname keyname

25
ReadParse Subroutine in cgi-lib

• ReadParse Subroutine
• Reads in Both Get and Put Data
• Converts Encoding to Plain Text
• Puts Key/Value Pairs in in
• in is an Associative Array
• To Access a Value
• in keyname
• To Access Each Key/Value Pair
• foreach keyname (sort keys (in))
• print keyname in keyname
• Example

26
In Class Exercise

• Modify Last Weeks Script to Accept User Name via
  a Form
• Step 1 Install cgi-lib in Your bin Directory
• Make Sure to Set Permissions Correctly
• Step 2 Make a Copy of perl1.pl
• Name it perl2.pl
• Step 3 Edit perl2.pl
• Add these lines
• require (cgi-lib.pl)
• ReadParse()
• Replace mynamexxx with
• myname in username
• Copy it to Your Shorenet cgi-bin directory

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In Class Exercise (2)

• Step 4 Create a Simple Form To Accept User Name
• lthtmlgtltheadgtlt/headgtltbodygt
• ltform methodpost actionhttp//users.shore.net/
  brinetxx/cgi-bin/perl2.plgt
• Enter name ltinput typetext nameusername
  valuedefaultgtltbrgt
• ltinput typesubmit Valuesubmitgt
• lt/formgt
• lt/bodygtlt/htmlgt
• Copy it to Your Shorenet Public_html Directory
• Step 5 Try It!
• When You Are Done
• Review Sample Scripts / Demos