1. Guide To UNIX Using Linux Third Edition
Chapter 9:
Perl and CGI Programming
Guide To UNIX Using Linux Third Edition

2. Objectives Understand the basics of the Perl language
Identify and use data types in Perl scripts
Understand differences between the Awk program and Perl programming
Guide to UNIX Using Linux, Third Edition

3. Objectives (continued)
Access disk files in Perl
Use Perl to sort information
Set up a simple HTML Web page
Understand how Perl and CGI are used for creating Web pages
Guide to UNIX Using Linux, Third Edition

4. Introduction to Perl
Perl contains features found in other languages – it is very similar to C and also contains features found in Awk and shell programs
Guide to UNIX Using Linux, Third Edition

5. Introduction to Perl (continued)
Perl can be directed to read its input from the keyboard
Guide to UNIX Using Linux, Third Edition

6. Introduction to Perl (continued)
Perl uses decision structures such as if statements to control program flow
Guide to UNIX Using Linux, Third Edition

7. Introduction to Perl (continued)
Guide to UNIX Using Linux, Third Edition

8. Introduction to Perl (continued)
Guide to UNIX Using Linux, Third Edition

9. Identifying Data Types
Data may be represented in Perl in a variety of ways:
Variables and constants
Scalars
Numbers
Strings
Arrays
Hashes
Guide to UNIX Using Linux, Third Edition

10. Variables and Constants
Variables and constants are symbolic names that represent values stored in memory
The value of a variable can change while the program runs
The value of a constant does not change while the program runs
Guide to UNIX Using Linux, Third Edition

11. Scalars Scalars are simple variables that hold a number or a string
A string is any nonnumeric sequence of characters (including numbers treated as characters)
Scalar variable names begin with a dollar sign ($)
Guide to UNIX Using Linux, Third Edition

12. Numbers
Numbers are stored as either signed integers, or as double-precision floating-point values
Numeric literals can be either integers or floating-point values
Perl uses an added convention with numeric literals to improve legibility: the underscore character (_)
Guide to UNIX Using Linux, Third Edition

13. Strings Sequences of any types of characters
Often used for logical analysis, sorts, or searches
String literals are usually delimited by either single (‘) or double quotes (“)
To put control and escape characters into strings, need to use \ notation, e.g., \n is a newline character
Guide to UNIX Using Linux, Third Edition

14. Strings (continued)
Guide to UNIX Using Linux, Third Edition

15. Strings (continued)
The use of special codes determined the output of this Perl script
Guide to UNIX Using Linux, Third Edition

16. Arrays
Variables that store an ordered list of scalar values accessed with numeric subscripts
An at sign precedes the name of an array when assigning it values
Use the dollar sign ($) when processing the individual elements of an array
Subscripts are zero-based
Guide to UNIX Using Linux, Third Edition

17. Hashes Variables that represent key/value pairs
A percent sign (%) precedes the name of a hash variable when assigning it a value
Use the dollar sign ($) to refer to a single element of a hash
Guide to UNIX Using Linux, Third Edition

18. Perl versus the Awk Program
This Awk program counts comment lines in a file. Awk doesn’t use while-type statements for looping.
Guide to UNIX Using Linux, Third Edition

19. How Perl Accesses Disk Files
Perl uses filehandles to reference files
A filehandle is the name for an I/O connection between Perl and the OS
Used to open, read, write, and close a file
3 standard filehandles: STDIN, STDOUT, STDERR
Guide to UNIX Using Linux, Third Edition

20. How Perl Accesses Disk Files (continued)
Can open a file
With an explicit open statement
By providing the file name at the command line (storing it in ARGV[0])
Should always check for failure or EOF when opening a file
Guide to UNIX Using Linux, Third Edition

21. How Perl Accesses Disk Files (continued)
Perl can access a file by passing the filename on the command line
Guide to UNIX Using Linux, Third Edition

22. Using Perl to Sort Perl has a powerful sort operator
Can sort strings or numbers
Can sort in ascending or descending order
Advanced sorting operations allow you to define your own sorting routine
Guide to UNIX Using Linux, Third Edition

23. Using Perl to Sort Alphanumeric Fields
You can sort words in a Perl program into alphabetical order using the sort function
Guide to UNIX Using Linux, Third Edition

24. Using Perl to Sort Numeric Fields
You can sort numeric fields in a Perl program by using a sort subroutine
Guide to UNIX Using Linux, Third Edition

25. Setting Up a Web Page
Web pages can be created using HTML (Hypertext markup Language)
HTML is a format for creating documents with embedded tags
Tags give the document special properties when it is viewed in a Web browser
Guide to UNIX Using Linux, Third Edition

26. Setting Up a Web Page (continued)
Hyperlinks load another document into the browser when clicked
Web pages are published on a web server
Apache is a common Web server software
Linux has a loopback networking feature
Lets you access your own system as if it were an external network
Useful for testing Web pages before publishing
Guide to UNIX Using Linux, Third Edition

27. Creating a Simple Web Page
Two ways to create HTML documents:
Typing the text and desired embedded tags
Using a visual HTML editor
Two main parts to HTML code
Head contains the title, which appears on the top bar of the browser window
Body defines what appears in the browser window
Guide to UNIX Using Linux, Third Edition

28. Creating a Simple Web Page (continued)
An HTML document viewed in Mozilla
Guide to UNIX Using Linux, Third Edition

29. CGI Overview
CGI (Common Gateway Interface) is a protocol, or set of rules, governing how browsers and servers communicate
Scripts that send or receive information from a server need to follow the CGI protocol
Perl is the most commonly used language for CGI programming
Guide to UNIX Using Linux, Third Edition

30. CGI Overview (continued)
Perl scripts are written to get, process, and return information through Web pages (dynamic pages)
Main objects in dynamic Web pages are forms that allow you to collect input data from a Web page and send it to a server
Guide to UNIX Using Linux, Third Edition

31. CGI Overview (continued)
This Web page contains a form that collects information from a user to submit to a server via CGI
Guide to UNIX Using Linux, Third Edition

32. Chapter Summary
Perl is a interpreted scripting language that can be combined with CGI to create interactive Web pages
Perl blends features found in C, Awk, and shell programs
Perl includes
An if-else statement as a decision structure
Numeric and string relational operators
Arithmetic operators
Guide to UNIX Using Linux, Third Edition

33. Chapter Summary
Perl’s data types include numbers, strings, arrays, and hashes
Perl and Awk are both good for applications requiring pattern matching
Unlike Awk, Perl includes an explicit while looping structure
Perl includes a powerful sort feature
Guide to UNIX Using Linux, Third Edition

34. Chapter Summary
Web pages are created using Hypertext Markup Language (HTML)
An HTML document contains embedded tags that specify document properties and links to other pages
CGI is a protocol or set of rules governing how browsers and servers communicate
Guide to UNIX Using Linux, Third Edition