Chapter%20Nine

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Chapter Nine

• Perl and CGI Programming

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Lesson A

• Learning to Use Perl

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Objectives

• Understand the basics of the Perl language
• Identify and use data types in Perl scripts
• Understand the difference between the Awk program
  and Perl programming

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Objectives

• Create simple Perl scripts with variables and
  logic structures
• Create simple Perl scripts to read and sort data
  files

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Introduction to Perl
Perl contains a features found in other languages
it is very similar to the C and also contains
features found in Awk and shell programs
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Introduction to Perl
Perl can be directed to read its input from the
keyboard
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Introduction to Perl
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Introduction to Perl
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Identifying Data Types

• Data may be represented in Perl in a variety of
  ways
• Variables and constants
• Scalars
• Numbers
• Strings
• Arrays
• Hashes

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Identifying Data Types

• Variables are symbolic names that represent
  values stored in memory
• The value of a variable can change while the
  program runs constants do not change
• Scalars are simple variables that hold a number
  or a string
• Scalar variable names begin with a dollar sign ()

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Identifying Data Types

• 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 added convention with numeric literals
  to improve legibility the underscore character
  (_)

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Identifying Data Types

• Strings are sequences of any types of characters
• Strings are often used for logical analysis,
  sorts, or searches
• String literals are usually delimited by either
  single () or double quotes ()

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Identifying Data Types
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Identifying Data Types
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Identifying Data Types
The use of special codes determined the output of
this Perl script
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Identifying Data Types

• Arrays are variables that store an ordered list
  of scalar values that are accessed with numeric
  subscripts
• An at sign (_at_) precedes the name of an array when
  assigning it values
• Use the dollar sign () when processing the
  individual elements of an array

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Identifying Data Types

• Arrays are variables that represent a set of
  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

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Perl versus the Awk Program
The Awk program uses fewer lines of code to
resolve pattern-matching extractions than does
Perl
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How Perl Accesses Disk Files
Perl uses filehandles to reference files, as
shown in this figure
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Using Perl to Sort
You can sort words in a Perl program into
alphabetical order using the sort function
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Using Perl to Sort
Perl can access a file by passing the filename on
the command line
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Using Perl to Sort
You can sort numeric fields in a Perl program by
using a sort subroutine
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Lesson B

• Creating an Interactive Web Page

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Objectives

• Set up an HTML Web page
• Use Perl and CGI scripts to make your web pages
  interactive
• Use X Window and Netscape to retrieve Web pages

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Setting Up a Web Page

• Web pages can be created using HTML (Hypertext
  markup Language)
• HTML is a format for creating documents with
  embedded codes known as tags and when the
  document is viewed in a Web browser, the tags
  give the document special properties
• After using HTML to create a Web page, the page
  is published on a Web server, this allows others
  to access the document via the Internet

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Creating a Web Page

• HTML documents are created by typing its text and
  the desired embedded tags
• There are two parts to the HTML code
• The head contains the title, which appears on the
  top bar of the browser window
• The body defines what appears within the browser
  window

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Creating Web Pages
An HTML document viewed in Netscape Navigator
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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
• Perl scripts are written to get, process, and
  return information through Web pages

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Chapter Summary

• Perl is used as a powerful text-manipulation tool
  similar to the Awk program
• Perl is written in scripts that are translated
  and executed by the Perl program
• The Perl programmer has to write process-handling
  instructions for data items to prevent
  misidentification of data types and subsequent
  processing errors
• Perl has three basic data types scalars, arrays,
  and hashes

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Chapter Summary

• A list is an ordered group of simple variables or
  literals, separated by commas
• Anything besides a textual sort must be handled
  with a sort subroutine
• An HTML document contains two parts a head and a
  body
• CGI is a protocol or set of rules governing how
  browsers and servers communicate
• To run your Web pages, you need to be in X Window
  and have access to a Web browser