Introduction to CGI

CGI stands for "Common Gateway Interface," a fancy name meaning computer programs running on the web server that can be invoked from a www page at the browser. The "bin" part alludes to the binary executables that result from compiled or assembled programs. It is a bit misleading because cgi's can also be Unix shell scripts or interpreted languages like Perl. CGI scripts need to be saved in ASCII format and uploaded to your server's cgi-bin in ASCII or text format. This is very important.

Where to Put CGI Scripts

Put your cgi-bin scripts in the www subdirectory named "cgi-bin".

Paths to Date, Mail, Perl, etc.

Here are your paths to the common server resources that CGI scripts often require:

Permissions - Definitions and Overview

In order for your CGI program to run, it must be executable by the server. Therefore, you must set the permissions so the server can read or execute your files, which usually means making your CGI programs world executable. The way you set your file permissions is by using the CHMOD commands.

The CHMOD�s permission mask is a three-digit number. Each digit of the number defines the permission for a different user of the file. The first digit defines the permission for the owner, the second digit defines the permissions for the group and the third digit defines the permissions for everyone else (referred to by CuteFTP as public). Each digit works the same for each group of users: the owner, group, and public. What you set for one digit has no effect on the other two digits.

Owner = the files users (you)
Group = the files group
Others = others

Permissions Definitions:

r = read access
x = execute access
w = write access

Numerical Definitions:

r = 4
x = 2
w = 1

You will come to recognize, if you do not already, Chmod as a word used for changing Permissions from within Telnet or your FTP client.

Some scripts will tell you to chmod 775 (for example). When using the numeric system, the code for permissions is as follows:

4 + 2 + 1 (rwx) = 7

The first number applies to Owner, the second number applies to Group, and the third number applies to Others. Therefore the first 7 of the chmod 775 tells Unix to change the Owner's permissions to rxw (because r=4 + w=2 + x=1 adds up to 7, this giving the Owner Read, Write, and Execute Permission. The second 7 applies to the group, this giving the Group Read, Write, and Execute Permission, and the last number 5, refers to Others (4 + 1= 5), giving Others only Read and Execute Permission. The permissions for chmod 775 look like this: rwx rwx -rx.

Permissions are always broken up into three groups of letters, however if there is a dash, this dash simply means that Permission wasn't given for that particular function, for example in the chmod 775, Permission to Write was not given to Others.

Remember: the first 3 letters always apply to Owner, the second 3 apply to Group, and the third 3 apply to Others.

 

Setting Permissions

• File Manager
• FTP
• Telnet. We DO NOT encourage the use of Telnet if it is only being used for setting permissions and will forego its explanation here.

Setting Permissions Using Your File Manager:

Log into your Control Panel and then click on File Manager. You will now see a list of directories within the root of your account. Since all of your html files and subdirectories are uploaded and created within your www directory you need to click on the directory labeled "www".

Once inside your www folder, you will see, as in all directories, the first column is the Permissions Column, click on the link pertaining to the directory or file that you wish to set the settings for and the Permissions screen. (Refer to Permission Definitions further down this page for an explanation of settings.)

Troubleshooting CGI-bin Problems

Below are solutions to some of the more common CGI script problems.

When I activate my CGI program, I get back a page that says "Internal Server Error. The server encountered an internal error or mis-configuration and was unable to complete your request."

This is generally caused by a problem within the script. Check your script settings again to see that you have entered the correct server information and have set the correct permissions for the script. If this information is correct, you'll need to contact whoever wrote or is distributing the script for further assistance.

I am being told "File Not Found," or "No Such File or Directory."

Upload your Perl or CGI scripts in ASCII mode, not binary mode.

When I test my Perl script in local mode (by Telnet), I have the following error: "Literal @domain now requires a back slash at myscript.pl line 3, within string. Execution of myscript.pl aborted due to compilation errors."

This is caused by a misinterpretation by Perl. You see, the "@" sign has a special meaning in Perl; it identifies an array (a table of elements). Since it cannot find the array named domain, it generates an error. You should place a back slash (\) before the "@" symbol to tell Perl to see it as a regular symbol, as in an email address.

I am getting the message "POST not implemented."

You are probably using the wrong reference for cgiemail. Use the reference /cgi-bin/cgiemail/mail.txt. Another possibility is that you are pointing to a cgi-bin script that you have not put in your cgi-bin directory. In general, this message really means that the web server is not recognizing the cgi-bin script you are calling as a program. It thinks it is a regular text file.