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CGI Programming FAQ

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The Table of contents starts at 0 (preamble). Older (pre-HTML 3) or broken browsers may start it at 1: apologies for any confusion.

Table of Contents

  1. Preamble
    1. Changes
    2. Notice and Disclaimer
    3. Where to get this document
    4. How to contribute to this document?
    5. Can I email the author my questions?
    6. What's up with posting to comp.infosystems.www.authoring.cgi?
    7. Credits
  2. Basic Questions
    1. What is CGI?
    2. Is it a script or a program?
    3. When do I need to use CGI?
    4. Should I use CGI or JAVA?
    5. Should I use CGI or SSI or ... { PHP/ASP/... }
    6. Should I use CGI or an API?
    7. So what are in a nutshell the options for webserver programming?
    8. What do I absolutely need to know?
    9. Does CGI create new security risks?
    10. Do I need to be on Unix?
    11. Do I have to use Perl?
    12. What languages should I know/use?
    13. Do I have to put it in cgi-bin?
    14. Do I have to call it *.cgi? *.pl?
    15. What is the "CGI Overhead", and should I be worried about it?
    16. What do I need to know about file permissions and "chmod"?
    17. What is CGIWrap, and how does it affect my program?
    18. How do I decode the data in my Form?
  3. HTTP Headers and NPH Scripts
    1. What is HTTP (HyperText Transfer Protocol)?
    2. What HTTP request headers can I use?
    3. What Environment variables are available to my application?
    4. Why doesn't my script get REMOTE_USER? My page is password-protected.
    5. What HTTP response headers do I need to know about?
    6. What is NPH?
    7. Must/should/can I write nph scripts?
    8. Do I have to call it nph-*
    9. What is the difference between GET and POST?
  4. Techniques: "How do I..."
    1. Can I get information about who is visiting?
    2. Can I get the email of visitors?
    3. "But I saw display my email address..."
    4. Can I verify the email addresses people enter in my Form?
    5. Subject: How can I get the hostname of the remote user?
    6. Can I get browser details and return different pages?
    7. Can I trace where a user has come from/is going to?
    8. Can I launch a long process and return a page before it's finished?
    9. Can I launch a long process which the user interacts with?
    10. Can I password-protect my pages?
    11. Can I do HTTP authentication using CGI?
    12. Can I identify users/sessions without password protection?
    13. Can I redirect users to another page?
    14. Can I run a CGI script without returning a new page to the browser?
    15. Can I write output to a different Netscape frame?
    16. Can I write output to several frames at once?
    17. Can I use a CGI script to generate both text and inline images?
    18. How can I use Caches to make CGI scripts faster and more Net-friendly?
    19. How can I avoid users hitting "submit" twice?
    20. How can I stop my CGI script reading and writing files as "nobody"?
    21. How can I prevent my CGI results being cached by the browser?
    22. How can I control the default filename when downloading a file via CGI?
  5. Troubleshooting a CGI application
    1. Are there some interactive debugging tools and services available?
    2. I'm having trouble with my headers. What can I do?
    3. Why do I get Error 500 ("the script misbehaved", or "Internal Server Error")
    4. I tried to use (Content-Type|Location|whatever), but it appears in my Browser?
    5. How can I run my CGI program 'live' in a debugger?
    6. I'm using CGI with QUERY_STRING embedded in my HTML, but it gets corrupted?
  6. Further Reading
    1. Other FAQs/collections
    2. Reference Pages

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