IT350 - Web and
Lab 8 ? CGI with Perl
This week will be an
introduction to CGI programming. To do this, you will go back to the HTML form
you created for your website back in Lab 02/03, and finally put some computation
behind it ? to really keep track of signups, orders, etc.
You originally created your
form in Lab02, though you should copy
your work from Lab03 (or later) instead, in order to benefit from your
later CSS additions.
IMPORTANT: You are likely editing your Perl files on a Windows machine. On
Windows, files are usually save in "DOS" mode, which means each line
ending is actually two characters (CR/LF). On Unix, only one character is used,
and our Unix-based web server will fail on any files saved in Windows mode. For
- Do not use Notepad! Use Notepad++
- In Notepad++: Settings->Preferences->New
Document/Default Directory tab. Select "Unix" for format. Note
that you must do this BEFORE you create your Perl file, but then it should
remember the setting on that computer. If you already have a file in
Dos\Windows mode (look on the status bar at the bottom of the screen),
then do this: Edit->EOL Conversion->UNIX format.
- Whatever tool you use: do this change on your Bancroft
machine as well.
You must create a folder on you Web drive called
"Lab08" (without the quotes) and store your work in that directory.
IMPORTANT: To allow the webserver to later create files when
running a perl script, the webserver user needs to have extra permissions on
your Lab08 directory. To enable this, ssh into intranet.cs.usna.edu (use putty
or other tool) and type the following in the window that appears:
setfacl -m u:www-data:rwx Lab08
Read the entire lab so you see the requirements and
know what is coming.
first order of business is to write a basic Perl program and get that
working to the point where it produces some output visible with a browser.
We?ll walk you through this part:
- Right-click on submit and then save it in
W:\public_html\Lab08\submit.pl (you must
change ?Save as type? to ?All files?.
Then change filename from submit.txt to submit.pl)
a look at submit.pl. Get a general
feel for what it does. (Note: it
has a few bugs that you will correct in a moment).
into intranet.cs.usna.edu (use putty or other tool)
the following into the window that appears:
(this will execute your file. Any syntax error will be
reported to the screen)
If you cannot execute submit.pl
due to permissions errors, use
chmod 755 submit.pl
to set the correct permissions for
last step should identify a few errors in the program. Fix them. Re-run perl from the command line until
you get no more errors. (Hint: all control flow statements like
if/while/for require curly braces around their body ? this is optional in
most other languages).
fetching the URL http://intranet.cs.usna.edu/~mXXXXXX/Lab08/submit.pl?name=Fred&age=72
You likely still have a logic bug or two in your program that perl
interpreter won?t catch. Fix the
program so that fetching the above link correctly produces the following
output (note: if you get nothing and have the right URL, use the next
step to debug your Perl):
a syntactically correct Perl program will still crash when you run it
with actual parameters, in which case you may not be able to see
everything/anything when you run it via the browser, as in the step
above. At such times, you want to
instead really run it from the command line, but provide arguments so
that it actually execute the right thing.
To do that, we omit the question mark from the URL and just
provide the arguments as a quoted string like this:
Try this out now and see what the output looks like. This is a vital debugging tool, and you
will want to use this for your final project and possibly for this lab.
- Congratulations! You now have a working CGI program.
Before moving to the next part, show your instructor your working program.
You will now modify it to use the
values provided by your form.
- Perl functions: You are required
to write and use at least one Perl function for this lab.
should have a file form.html from Lab03, copied into Lab08. Your form
should contain at least on element of the following input types: text,
password, checkbox or radio button, submit (your form will likely contain
more than that) Modify the form (in your Lab08 directory) so that when you
click submit, it invokes your new CGI program. Modify your CGI program so that it reads
in some value from your form and displays the value in its resultant HTML
check: Modify submit.pl
to validate some of the input
that your form provides to your CGI program. If an error is detected, your program
should state explicitly what the error was, and tell the user to hit the
back button and try again (see extra credit for a better approach). You
may find it useful to go back to Lab03/form.html, fill in some values, and
click submit to see how your data is received by the CGI program we gave
you earlier. For the validation you should at a minimum check the
following (you can of course do more if you like):
your first (or only) text field, ensure it is filled out (not empty)
your first (or only) set of checkboxes OR radio buttons, ensure at least
one checkbox / radio button is selected. See the "Hints"
section for a discussion about checkboxes.
least one of your checks must involve a pattern match / regular
expression ? e.g. to verify a phone number, SSN, etc. is valid. See section 25.3 of the online book
chapter. You may also find the
validation in Figure 25.13 useful.
You can modify your form if you wish (to create a parameter that
is more amenable to validating with a pattern match).
Modify your Perl code so that, if the variables pass all the
validation tests above, the program prints out a user friendly
confirmation. This confirmation
should display the value of all the variables that were provided in
a user-friendly manner.
A page with a raw list of variables
and their values is not so friendly -- you should at least have a
reasonable title, some welcome text, then a reasonable confirmation of
their values. Imagine this was on your website and you wanted to present a
reasonable appearance to someone that just submitted your form. Example: ?Your reservation for 4 people
has been confirmed. The details for
this reservation are as follows??
Modify submit.pl so that it records activity to a file called LOG.txt.
You will want to append to this file (so it contains a history of
everything that has happened). If the values pass your ?Validity? test,
then write all the parameters provided by the user to LOG.txt. The values provided by a single user
should all be on a single line ? use a tab (?\t?) as a separator. Hint:
Create a function to write into the log
Here?s an example of how a simple Log file might look after 3 users
submitted forms that passed the Validity test:
ensure you have appropriate comments.
final step: create five links in your top-level default.htm page under
the heading ?Lab08?
the name ?Form?, make a link to your Lab08/form.html page
the name ?Good submission? make a link to your submit.pl file with all of
form variables specified in the URL, such that variables all
validate. Hint: if your form uses
the GET method (change this temporarily if necessary), then you can
create the needed URL for this by filling out your form correctly and
the name ?LOG.txt? make a link to your log file
Your HTML web page must be constructed using Notepad or a
similar text-only editor. The use of programs such as Microsoft Word,
Microsoft Frontpage, DreamWeaver, ColdFusion, Mozilla Composer, etc. will be
considered an honor offense.
For a nominal amount of extra credit do some/all of the
(NOTE: saving a backup copy of your working lab is recommended before starting
your program finds a validation problem with an input (such as a missing
value or a number that is too big), a much better way to handle this is to
have your CGI program regenerate the table with all of the values provided
by the user filled in, and values that had a problem highlighted. Of course there should be a submit
button so the user can modify the values and resubmit back to the CGI
a new CGI program (in Perl) that reads your LOG file and generates a
summary report of the submissions.
Be sure that your LOG.txt has enough data in it to make this report
at least a little interesting.
- Your main web page should be
called "form.html" (without the quotes).
- Your Perl file should be
- You should have all the
pieces working described in ?Requirements? above.
- You should have the three
links in default.htm that are described above.
- All of your files should be
in a folder called "Lab08" (without the quotes) on the W drive. Your
instructor will assume that your web pages are viewable at
http://intranet.cs.usna.edu/~mXXXXXX/Lab08/form.html where XXXXXX is
your alpha number. You may want to check that this URL is viewable and
that everything works correctly from a computer where somebody else is
logged in. If you've goofed and linked to a file on your X drive, this
will help you catch it!
- Turn in the following
hardcopy at the beginning of class on the due date, stapled together in
the following order (coversheet on top):
- A completed assignment
coversheet. Your comments will help
us improve the course.
- A printout of the
source to your submit.pl file.
are interesting because more than one can be checked. If you give the same
name (in HTML) to all your checkboxes, for example ?mychecks?, and if you
write something like this in Perl:
the param() function will notice the result should be an array (due to the
@ symbol), and will return an array with the values of all of the
?mychecks? checkboxes that were checked.
your code is not working, first run perl from the command line (like you
did in the beginning of the lab) to ensure there are no syntax
errors. Then, add extra print()
commands to see what parts of the program are executing and what the
values being used are.
book sometimes use the die()
function to report errors. This is
a bad idea for CGI programs because the script will just terminate without
sending the error message to the browser.
Instead, use regular print()
commands to send an error.