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CGI-bin
Applications
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-bin Scripts
Put
your cgi-bin scripts in the www or public_html subdirectory
named "cgi-bin".
Common
Paths to Date, Mail, Perl, etc.
Here
are your paths to the common server resources that CGI scripts often
require:
| Sendmail:
|
/usr/sbin/sendmail |
| /usr/lib/sendmail |
| Perl5.003: |
/usr/bin/perl |
| Perl5.004: |
/usr/bin/perl5.004 |
| Date: |
/bin/date |
| Java: |
/usr/local/java/bin/java |
| Python: |
/usr/bin/python |
| Domain path: |
/www/yourdomain |
|
(puts you in your web directory)
|
| Cgi-bin path: |
/www/yourdomain/cgi-bin |
|
(puts you in your cgi-bin) |
Look
at the window in your FTP or Telnet client to see whether your site
resides on /home/ or /home2/.
Setting
Permissions
The
following is a simple explanation of file permissions in Unix. To
list the access permissions of a file or directory, telnet to your
server, then:
cd
directoryname
to
change the directory until you are either in the directory above the
file you are interested in, or above the directory you are checking.
Type:
ls -l filename
and
you will see what the current permission settings are for that file,
along with a bunch of other stuff.
Examples
of using chmod:
| PEOPLE |
PERMISSIONS |
| u
= the file's user (you) |
r
= read access |
| g
= the file's group |
x
= execute access |
| o
= others |
w
= write access |
| a
= the user, the group, and others |
|
To
change permissions for a file named filename.cgi, you need to chmod
the file (change mode). For example, when you type this:
chmod
u=rwx,g=rx,o=rx filename.cgi
you've
given:
read, execute, and write access to the user (that's you)
read and execute access to the group and
read and execute access to others
Some
scripts will tell you to chmod 775 (for example). Doing the above
is the same thing as typing chmod 775. You can use either method with
our Unix servers. Let me explain:
When
using the numeric system, the code for permissions is as follows:
r
= 4 w = 2 x = 1 rwx = 7
The
first 7 of our chmod775 tells Unix to change the user's permissions
to rxw (because r=4 + w=2 + x=1 adds up to 7. The second 7 applies
to the group, and the last number 5, refers to others (4+1=5).
When
doing an ls -l on the file, telnet always shows the permissions this
way:
-rwxr-xr-x
Ignore
the first dash, then break up the above into three groups of letters.
If there's a dash where a letter should be, it means that there is
no permission for those people.
Remember:
the first 3 apply to user, the second 3 apply to group, and the third
3 apply to others.
Some
FTP clients support changing permissions in a more graphical way.
If you have Fetch for the Mac, you have an easy way to change permissions.
Go to the file you want to change the permissions on, and highlight
it. Under the Remote menu, select Change Permissions. A window will
pop up showing the current permissions for the file you had highlighted,
as in Figure 3A below. Click on the boxes to change permissions
as needed.
Figure 3A
WS_FTP
accomplishes the same task as above. Just highlight the file you want
to check, and right-click on it. A menu will pop up, then select CHMOD.
You will see the window below, as in Figure 3B.
Figure 3B
Appendix
Permission
Settings
Troubleshooting
CGI-bin Problems
Below
are solutions to some of the more common CGI script problems, in question
and answer format.
When
I activate my CGI program, I get back a page that says "Internal
Server Error. The server encountered an internal error or misconfiguration
and was unable to complete your request."
Upload
your Perl or CGI script in ASCII mode, not binary mode.
I
am being told "File Not Found," or "No Such File or
Directory."
Upload
your Perl or CGI script 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 backslash 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 backslash (\) 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.
