CSC
112 - Lesson 3
Don't Reinvent the Wheel
The greatest thing about the web is what you can find on it.
You can find graphics, programs, scripts, templates and just about
anything that you might need to power a web site or web application.
Some are free. Others are minimal cost and yet others are outrageously
expensive. But if you look hard enough, you are likely to find
something within your budget, even if your budget is zero.
I am not saying that you shouldn't write your own programs or
make original graphics or anything like that but what I am saying
is... if you don't have the time or the money to do it yourself,
use programs and other tools to do what you want to do.
This is nothing new. I've heard that the difference between monkeys
and men is, men (and women) use tools. All I am saying is that
you should use the tools available to you on the web.
CGI-Scripts
There are many free CGI script sites where you can download ready
made programs for things such as bulletin boards, chat rooms,
shopping carts, games, email lists, calendars and just about anything
else you might want your web application to do. The people who
wrote these scripts spent hundreds and in many case thousands
of hours writing these scripts so you don't have to.
Easy to do
Getting a scripts running on your site is relatively easy to
do. The first time or two, you might make a few mistakes but after
you do it a few times you'll be amazed how easy it actually is.
Perl
One of the main scripting languages for use in CGI is called
Perl. Perl is a noncompiled language similar to HTML and JavaScript.
The main difference is HTML and JavaScript are client side technologies
(the code runs in your browser and loads when your page loads).
Whereas Perl runs on the server so the server must be called whenever
you run the program over the web.
Setting up a Perl Script in a Nutshell
1.) The first thing you need to do is to find a perl script that
you want to use on your web site. Scour the search engines. Search
for "free perl scripts", "free cgi scripts"
or just "perl scripts"
A few places to start are:
2.) Download the script that you want to use to your computer.
It will be in one of 4 forms:
Text file - These are the most basic scripts. You may need to
change the *.txt extension to *.cgi or .pl or your script may
almost be ready to run. When you upload (or download) your script
to your cgi-bin on you server, be sure to use the ASCII mode on
your ftp program. CGI programs transfered in binary mode will
not run in your cgi-bin. Edit you program in a simple text editor
like Notepad.
Zip file - You all know this type. You download it to your computer.
Then use your Windows or Macintosh unzipping program. In class
we use WinZip, but you can use any zip program that you may have.
Extract your program to the directory where you want to save your
program. The upload it in the ASCII mode (see warning above).
TAR - TAR is like zip but for UNIX or Linux. You download it
to your computer then upload it to the directory in your cgi-bin
where you want it to go. On UNIX systems, you any type in the
following command:
tar xvfp yourprogram.tar
The TAR program installed on your server will unpack all of your
files and directories expanding them into their proper places
inside of the current directory. TAR programs always use the *.tar
extension. The letters "xvfp" in the TAR command tell
the computer to extract the files and directories and to set the
permissions to the original settings. The "x" is the
command that tells TAR to extract the files. The "v"
command tells TAR to output information about the status of the
extraction during the process. The "f" tells TAR to
use the tar filename as the source to be extracted and the "p"
tells TAR to maintain the original permissions. After you do this
command, all the files should be neatly in their folders.
GUNZIP - Many cgi-scripts are compressed for download in the
GUNZIP format. Gunzip is like a supercompression program that
compresses TAR files even farther. gunzip files always end in
the *.gz extension. To open a gunzip file, in your command prompt
simply type in:
gunzip filename.gz
or
gunzip filename.tar.gz
The first command will uncompress your file into a TAR file and
you will need to use the tar method above to extract your files
to finish the process. The second command will use gunzip and
tar to do the same in one step. Be aware that using the second
method may require that you set your permissions because the original
permissions may not be maintained.
Note: You will need to use a TELNET or SSI program to get to
the UNIX prompt on your server to untar or ungunzip your files.
In class we use putty.exe which can be downloaded for free on
the PuTTY
Download Page.
To use putty, just type in your IP address or domain name and
click the SSI box and click the open button. This will get you
on the server. Use your password and login to get into your account.
If you need to, read UNIX
Guru in 20 minutes to learn the simple UNIX commands you will
need to get around on the server but I'll go over the basics here
for you.
3.) Use the list command (ls) to see where you are and to see
what directories and files are in the directory you are in.
To change to another directory use the change directory command
(cd directoryname). On our class web site you will need to type
in "CD www" then "CD cgi-bin" to get into
the cgi-bin or you could have done it in one step by typing:
CD www/cgi-bin
When you get there, type in "Ls -l" to list all the
files and directories as well as their permissions. Often copying
and expanding your files into directories is not enough to make
your scripts run. You may need to set the permissions and give
users the appropriate rights to each of your files.
If you are having trouble getting you script to run and you
just want to get everything working, type in:
chmod 777 *.*
to open everything up so permissions will be readable and writable
to everyone. After you get your script running you can go back
and redo the permissions.
| Common
Permission Settings |
| Permissions |
Command |
| User |
Group |
World |
|
| rwx |
rwx |
rwx |
chmod 777 filename |
| rwx |
rwx |
r-x |
chmod 775 filename |
| rwx |
r-x |
r-x |
chmod 755 filename |
| rw- |
rw- |
rw- |
chmod 666 filename |
| rw- |
rw- |
r-- |
chmod 664 filename |
| rw- |
r-- |
r-- |
chmod 664 filename |
The value of the digit determines the permissions granted. Permissions
consist of three digits:
- 4 for Read
- 2 for Write
- 1 for Execute
By adding these digits together, you add up to the permissions
that make up the number in the code. For example: 4 + 2 + 1 =
7, which is read, write, and execute. 4 + 1 = 5 which is read
and write. The chmod "777 filename" command makes the
file readable, writeable, and executable for the owner of the
file (user). the group the file is in and the world.
In order to open your file for editing in UNIX, you will need
to use a UNIX text editor. I usually use one called PICO that
comes installed with UNIX
To edit your file, simply type in:
pico filename
Your file will open in the pico text editor for editing:
Editing your script
4.) Finding Perl - Sometimes the perl module is installed in
different folders on deferent servers thus sometimes you may need
to change the path to the perl module.
The first line of any perl script instructs the server where
to find the perl module. Typically it looks like:
#!/usr/local/perl
or
#!/usr/bin/perl
In order to find the path to the perl module on your server,
type in:
which perl
The server will tell you the closest perl module:
perl: /usr/bin/perl
Sometimes there are several versions of the perl module installed
on your server. In order to see all of the perl modules on your
system use the command:
whereis perl
This command might give the following output:
Perl: /usr/bin/perl /usr/local/bin/perl /usr/bin/perl4.036
/usr/local/bin/perl5.002
If you are looking for a specific version of perl to run your
script, you should use the "whereis perl" command.
Edit the first line to make sure the path is right to the perl
interpreter (module) on your server.
Saving your edited file
5.) When you are done editing your file, save your file by using
the "control o" command. Hold down the control key and
type the letter "o" and the server will ask you if you
want to save your file. Type in the letter "y" for yes.
You file is saved.
If you want to exit pico and not update your file, hold down
the control key and type the letter "x". The server
will ask you if you want to exit without saving the file. Type
in the letter "y" for yes or the letter "n"
for no.
Follow the Directions
For your first cgi perl script, try something simple first to
give you a little experience before you jump in to something more
complex. Try a script with only a one (or a few) files to learn.
That said, most programs that you download will have simple step
by step instructions for installing the program. Be careful and
follow the directions exactly. Usually the file will be called
something like README.txt or INSTALL.txt. Use Notepad or some
other text editor to read the file. I usually print this stuff
out so it is easier for me to follow the instructions.
Some programs are easier to install than others. Some programmers
write very good instructions and some don't. Since often times,
you are getting the script for free, you can't expect much support
so if you are having trouble with one script, try another.
Sometimes you might decide to buy a program to use instead of
using a free one. When you purchase a program or the license to
a program, often the company that wrote it will supply you with
support. Sometime spending a couple of hundred dollars on a program
might save you hundreds or even thousands of hours. Don't be afraid
to spend a little money to save your time and sanity. I buy programs
from time to time. It helps me get my tasks done much more quickly.
Many of these programs have been thoroughly tested and may be
more reliable than something you put together yourself. Keep an
open mind. For more information about installing cgi scripts see
The Most Simple
Intro to CGI and Your
First CGI Script from BigNoseBird.com.
Other languages and programs
Perl in not the only language on the web. You may find another
that you are more comfortable with and prefer using. Try your
hand at some others too. There are many free scripts on the web
to chose from in just about every language available
Installing someone else's scripts is a good way to get started
on some other languages. You not only get the benefits of the
program and its features but also you get a chance to learn from
the experts. What more could you ask? Experiment and learn. That's
the way of the web and of life in general.
Languages that are available to learn on the web:
- Perl
- C and C++
- AppleScript
- Python
- PHP
- Tcl
- UNIX Shell
- Visual Basic
- VBScript
- JavaScript
- DHTML
- JAVA
- and many more
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