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Perl Lecture Notes - December 8 - last 1st trimester class

• Questions

• Housekeeping
  • online gradebook is up to date for perl assignments
  • deadlines

• CGI Overview
  • This is a simply a preview of where we'll start next trimester.
  • CGI stands for "Common Gateway Interface". In practice, it means a "web application" - a program that runs on the server to generate the web page.
  • Example 1 : time.cgi (run it - source code) what time is it?
  • What's going on:
    1. browser sends HTTPD to bob port 80, "GET time.cgi ..."
    2. apache deamon runs "./time.cgi", collects STDOUT
    3. apache returns that with headers : "HTTP/1.1 200 OK ..."
  • The details include stuff like
    1. how to define apache's behavior - when it should do what
    2. how to pass in user input, typically from an HTML form
    3. how to return different kinds of stuff : text, html, images
    4. various techniques for cgi script itself (html within perl, perl within html, xml templates, ... )
    5. session management - tricks for remembering the visitor data
    6. various security issues
    7. ways of interacting with the filesystem and/or server-client database
    8. speed, number of connections, and scalability
    9. different web pages based on same content for browsers, PDA's, phones, ...
    10. getting inside the apache request cycle itself

  • Here are a few more examples, to wet your appetite.
    • Vanilla perl cgi scripts - perl program prints html
      (Many times something like this is all you need.)
      • On bob, all files ending in .cgi are executed (as if from the command line), and the output is the web page. Voila.
      • apache configuration
      • environment.cgi (run it - source code) displays %ENV hash - raw inputs to the script
      • form.html (run it - source html) demo of an HTML <FORM> block, typical way to get user input
      • slidingBlock.cgi (run it - souce code) a classic puzzle

    • mod_perl
      (For more speed or more in-depth control of request)
      • On bob, all files ending with .cgimp are run within mod_perl.
      • apache configuration
      • environment.cgimp (run it) symbolic link to same environment.cgi script
      • slidingBlock2.cgimp (run it - source code) small changes for the mod_perl environment
      • Another (big) example is the wiki, which is one big .cgi or .cgimp perl script. See the source at UseModWiki.pm.

    • HTML::Mason - an html file with bits of perl within it
      (When you're doing a whole web site. Many, many similar tools : Embperl, TemplateToolkit, PHP, ColdFusion, ...)
      • apache configuration
      • mason handler
      • The idea is that your web pages are built from "components": files whose html can be embedded within each other and/or treated like perl subroutines. Arguments to the subroutines are like name/value pairs passed in the URL. Perl code is embedded with the HTML, either on lines that start with % or within <%perl> XML-ish tags. I've set this up on bob as "file.mhtml" with a built-in session management hash $session{key}. Also, some file names are special: "autohandler" is always called; "dhandler" is called if a file isn't found. Powerful systems, but each takes time to learn...
      • mason/sample.mhtml (run it - source code)
      • mason/autohandler (source) - all files in this directory call this first
      • mason/nofile.mhtml (see it - dhandler source
      • mason/inner.mhtml?string=hello (see it - souce code) call a mason component from its url
      • (The online gradebook is an HTML::Mason application.)

• Readings (Entirely optional - we will be starting in somewhere in here when the second trimester starts.)
  • Online:
    • Beginner's Guide to CGI Scripting with Perl (tutorial with very detailed instructions)
    • CGI Programming (another tutorial)
    • CGI.pm (documentation for standard perl module)
    • perldoc -q "cgi or web programming"
    • The nitty-gritty CGI specification
  • Dead trees:
    • CGI Programming with Perl, 2nd Edition, Ruelich et al
    • Writing CGI Applications with Perl, by Meltzner and Michalski
    • Perl Cookbook, chapter 19, CGI Programming

• Assignment:
  • Not this time. See you after the break...

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