CGI and Perl

1
CGI and Perl
2
What is CGI?

• CGICommon Gateway Interface
• CGI is a lightweight mechanism for communication
  between the web server and other programs (CGI
  scripts) that can be run on the server.

3
CGI

• Instead of pointing to an HTML file a URL may
  request that a CGI program is run on the server.
  CGI programs (or scripts) are commonly written
  in
• Unix - Shell, Perl, Tcl, C,C, Python, Ruby
• Windows - Visual Basic, Perl
• Mac - Applescript, C,C, Perl

4
Client server schema I.
5
Client server schema II.
6
Client server schema III.
7
What is Perl?

• Practical Extraction and Report Language
• An interpreted language
• Highly optimized for manipulating printable text
  but also able to handle binary data

8
Type of variable determined byleading special
character

• scalar
• _at_ indexed array lists
• associative array
• function

9
Two ways to sent data fromhtml form to CGI

• GET-mainly used for short queries. Input values
  are part of URL
• POST-will send data as input stream to the
  program
• More secure

10
An example

• http//babbage.cs.missouri.edu/cs2830/cgi-bin/co
  llect_student_data.cgi

11
Where should I put my CGIscripts?

• CGI scripts must be under the public_html
  directory.
• CGI scripts should be kept in separate
  subdirectory of the public_html directory tree.
  Ex. cgi-bin
• CGI scripts must have a ".cgi" extension.
• CGI scripts should have permissions of 705.
• CGI scripts should live in directories that have
  permissions of 705.

12
How to run perl scripts on babbage

• Perl is picky about permissions
• use chmod to make them
• either chmod 705 filename.cgi
• or chmod uwrX,g-rwx,orx filename.cgi
• To debug perl/cgi scripts in the browser, use
  this at the top of your scripts
• !/usr/bin/perl -wprint "Content-type
  text/html\n\n"
  use CGIuse CGICarp
  qw(warningsToBrowser fatalsToBrowser)
  

13
CGI and HTML

• If your CGI script is going to generate an HTML
  page, you must include this statement in the
  script
• print "Content-type text/html\n\n"