Difference between revisions of "CGI Scripting"

Latest revision as of 12:03, 19 October 2012

CGI Scripting

We currently run Perl5 for CGI scripting. Compiled C/C++ CGI executables are allowed, along with other available language interpreters (PHP, for example).

CGI scripts are a way of using programs to both generate web pages dynamically and process user input.

You can call a program written in C/C++ as a CGI script. To compile the code on our servers, you will need to log onto the server using SSH and use the GCC compiler suite.

We provide the environment so that you can develop scripts and programs. However, you are completely responsible for your development efforts. You are also responsible for adequate security. If your scripts, including scripts written by someone else and installed by you, allow users to inject malicious content onto your site, or do anything else that violates our [terms of service, we will terminate and remove the scripts at our discretion to ensure continued service for other customers on the server.

We do not offer any search scripts. You are welcome to install a CGI script to do this. There are several general search packages for Unix which could be invoked via a CGI script.

We support user CGI scripting and you can install your own form processing CGI script. NMS FormMail is one of many such scripts we know works with our service for handling email form processing.

We have MySQL available to all accounts. Your database name is the same as your account name. Your MySQL database is initialized when your account is created. There are many different publicly available CGI front-ends available for it, such as Adminer. If you use such a front-end, you should restrict access to it using htpasswd and put it in a directory that isn't the default installation directory to keep it hidden and secured.

See our MySQL FAQ or [1]MySQL Mirror Site for more information on using MySQL.

What are CGI scripts and how do I use them?

They are a way of using programs to both generate web pages dynamically and process user input.

You need to learn a little about how to program in a Unix environment either in C or a script language like Perl.

Can I use CGI scripts?

Yes, all new accounts can use CGI scripts.

Do I need to have you activate something so that I can run cgi-bin scripts on my account?

No. You already have the complete ability to install and execute your own scripts.

Will I have access to my own CGI bin directory to run Perl scripts?

Yes.

I'm having problems with my CGI script. What should I do?

In general, when you are working on modifying an example program, which is now failing but worked when you started, go back to the example exactly, copy it, and then modify it slowly until it stops working, then you will know what you did that caused the bug.

Here are a few things to check:

• Be sure to upload your scripts with your SFTP client in text/ASCII mode. Unix and Mac OS X use LF (line feed) to as an end of line marker, Macintoshes (before OSX) use a CR (carriage return) by itself, and Windows/DOS uses both CR+LF. Therefore, if you're not on a Unix, Linux, or OS X system, it's important to ensure that your SFTP client makes the line ending change for you. If you use a command line SFTP client, type "ASCII" before you send it. If you are using some form of GUI SFTP client, be sure that the ASCII transfer option is enabled. Please remember to switch back to binary before you download any executables.

• Be sure to set your script to executable. You can do that using the "chmod 700" command when logged in via SSH, or you can set the executable bit on using your SFTP client.

• If your script is not a binary executable, check the first line. If your script is a Perl script the first line must be "#!/usr/bin/env perl". If your script is a Bourne shell script you first line must be "#!/usr/bin/env bash". If your script is using another shell language check to make sure that the path name specified is valid. Also, make sure that it is the first line in the script (no blank lines or comments), and that the script was uploaded in ASCII mode.

• Try running your script from the command line. This will provide a basic syntax check of your script, and possibly more, depending on how much of the code relies on parameters or environment variables set by the web server. However, some scripts may produce run-time errors when invoked in this manner. If possible, modify your script to fail politely when run at the command line so that you can use this technique to debug it. If you are a more sophisticated programmer, you can write a test script to set the necessary environment variables and invoke your main script. If your script is Perl, running it from the command line will print out any syntax errors. If it works from the command line, but fails with an error 500 when you call it, it may be failing to open a file. One common gotcha is the use of tilde (~) within a Perl script to reference your home directory. Just use "/home/username/".

• Server side include scripts (the "exec cmd" variety) need to use a full path name to be able to correctly locate your file. For convenience server side includes are usually put in your personal cgi-bin directory. The path name will be something like "/home/username/cgi-bin/userscript".

• When in doubt: simplify. Reduce the number of subroutines and the amount of code involved to verify that you can invoke your script at all. Then as you can verify that you are getting to a certain point, start adding code back in.

What is a wrapper CGI script? Does it create any limitations on scripts possibilities?

It lets us give you the ability to run your own CGI scripts, without compromising our security. There are few, if any limitations imposed by such wrappers (i.e. most of your scripts will work).

Could you let me have a sample of (insert programming task here) for me to look at?

We recommend you search for a publicly available example or hire a web developer experienced with that task.

I would like to call a program written in C from a CGI script. What is the procedure for compiling the code on your machine?

Log onto the server using ssh and use the compiler GCC (GNU project C and C++ Compiler v2.4).

A minor note, just so that you understand the conditions under which we support development: We provide the environment so that you can develop script and programs, you are completely responsible for your development efforts.

I get the following error message, even trying your demo CGI: "suid attempt aborted! Reason: execve failed - Permission denied"

You need to make your script executable. If you're writing your script locally and uploading it via an SFTP client, you should be able to right-click on the file after it's been uploaded, choose "permissions," and change Owner Permissions to Read, Write, and Execute. If you're editing your script via SSH, cd to he cgi-bin directory, and type:

chmod 700 yourscript

This will correctly set the permissions for your script.

Do you offer any kind of search engine so that our customers can perform search amongst a database?

You are welcome to install a CGI script to do this. There are several general database packages for Unix which could be invoked via a CGI script.

Can we install our own development tools?

Yes, in your user directory.

What type of forms do you currently have available?

You can create any kind of form you want. We support user CGI scripting and you can install your own form processing CGI script.

Do you have support for mail forms?

You can check our Forms tutorial. Other form scripts work as well, though we recommend NMS.

I would like to set up an image map. What is the best way to do so?

You don't need CGI scripting to create an image map. It is much simpler to use HTML. Take a look here for an example: http://www.w3schools.com/TAGS/tag_map.asp

Can you run a WAIS gateway script on your server?

Yes you could, provided you obtained the script and installed it yourself.

We would like to be able to seach a database via a form. Do you offer such a capability?

We have mySQL, an SQL type database installed. There are many different publicly available CGI frontends available for it. A mySQL database is included with all accounts. Your database name is the same as your account name. Your mySQL database should be initialized when your account is created, so that you may immediately begin using it.

See our mySQL FAQ or mySQL Mirror Site for more information on using mySQL.

Can I use Active Server Pages on Hurricane Electric?

Due to economic and performance considerations, we do not offer support for ASP.

Is LWP installed? What about other modules?

You are welcome to install your own set of additional modules.

When you build modules, use the PREFIX option when generating Makefiles:

perl Makefile.PL PREFIX=/home/username/perl

then either set the PERL5LIB environment variable before you run scripts that use the modules/libraries (see the perlrun manpage) or say:

use lib '/home/username/perl';

Is it possible to invoke a script without using suid?

Yes, the suEXEC feature is on by default for newer accounts. You can see if suEXEC is enabled for your account by logging into the billing database at:

https://admin.he.net

Then click on Edit Virtual Host Options. Then choose the check box next to suEXEC and click on Change.

Once suEXEC is enabled in your account, and let's say the domain name for your account was squishypenguin.com, you would invoke your script with the URL:

http://www.squishypenguin.com/cgi-bin/userscript.cgi