FAQ: Frequently Asked Questions about CGI Programming

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Frequently Asked Questions on CGI Programming
---------------------------------------------

0.   Preamble
0.1. Changes
0.2. Notice and Disclaimer
0.3. Where to get this document
0.4. How to contribute to this document?
0.5. Can I email the author my questions?
0.6. What's up with posting to comp.infosystems.www.authoring.cgi?
0.7. Credits

1.   Basic Questions
1.1. What is CGI?
1.2. Is it a script or a program?
1.3. When do I need to use CGI?
1.4. Should I use CGI or JAVA?
1.5. Should I use CGI or SSI or ... { PHP/ASP/... }
1.6. Should I use CGI or an API?
1.7. So what are in a nutshell the options for webserver programming?
1.8. What do I absolutely need to know?
1.9. Does CGI create new security risks?
1.10. Do I need to be on Unix?
1.11. Do I have to use Perl?
1.12. What languages should I know/use?
1.13. Do I have to put it in cgi-bin?
1.14. Do I have to call it *.cgi?  *.pl?
1.15. What is the "CGI Overhead", and should I be worried about it?
1.16. What do I need to know about file permissions and "chmod"?
1.17. What is CGIWrap, and how does it affect my program?
1.18. How do I decode the data in my Form?

2.   HTTP Headers and NPH Scripts
2.1. What is HTTP (HyperText Transfer Protocol)?
2.2. What HTTP request headers can I use?
2.3. What Environment variables are available to my application?
2.4. Why doesn't my script get REMOTE_USER?  My page is password-protected.
2.5. What HTTP response headers do I need to know about?
2.6. What is NPH?
2.7. Must/should/can I write nph scripts?
2.8. Do I have to call it nph-*
2.9. What is the difference between GET and POST?

3.   Techniques: "How do I..."
3.1. Can I get information about who is visiting?
3.2. Can I get the email of visitors?
3.3. 	"But I saw some.kool.site display my email address..."
3.4. Can I verify the email addresses people enter in my Form?
3.5. Subject: How can I get the hostname of the remote user?
3.6. Can I get browser details and return different pages?
3.7. Can I trace where a user has come from/is going to?
3.8. Can I launch a long process and return a page before it's finished?
3.9. Can I launch a long process which the user interacts with?
3.10. Can I password-protect my pages?
3.11. Can I do HTTP authentication using CGI?
3.12. Can I identify users/sessions without password protection?
3.13. Can I redirect users to another page?
3.14. Can I run a CGI script without returning a new page to the browser?
3.15. Can I write output to a different Netscape frame?
3.16. Can I write output to several frames at once?
3.17. Can I use a CGI script to generate both text and inline images?
3.18. How can I use Caches to make CGI scripts faster and more Net-friendly?
3.19. How can I avoid users hitting "submit" twice?
3.20. How can I stop my CGI script reading and writing files as "nobody"?
3.21. How can I prevent my CGI results being cached by the browser?
3.22. How can I control the default filename when downloading a file via CGI?

4.   Troubleshooting a CGI application
4.1. Are there some interactive debugging tools and services available?
4.2. I'm having trouble with my headers.   What can I do?
4.3. Why do I get Error 500 ("the script misbehaved", or "Internal Server Error")
4.4. I tried to use (Content-Type|Location|whatever), but it appears in my Browser?
4.5. How can I run my CGI program 'live' in a debugger?
4.6. I'm using CGI with QUERY_STRING embedded in my HTML, but it gets corrupted?

5.   Further Reading
5.1. Other FAQs/collections
5.2. Reference Pages

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Send corrections/additions to the FAQ Maintainer:
Nick Kew <nick@webthing.com>
Last Update October 13 2008 @ 00:13 AM