IT350 - Web and
Lab 7 ? 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.
VERY IMPORTANT: You are likely editing your
Perl files on a Windows machine. On Windows, files are usually saved 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 this reason:
- 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
You must create a folder on you Web drive called
"Lab07" (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 Lab07 directory. To enable this, ssh into zee.cs.usna.edu
(use putty or other tool) and type the following in the window that appears:
setfacl -m u:www-data:rwx Lab07
You will have to repeat this
step every time you create a new directory where you want to allow the
webserver to create files!
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\Lab07\submit.pl (you must change ?Save as type? to ?All files?. Then change filename from submit.txt to
Take 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).
ssh into zee.cs.usna.edu (use putty or other
the following into the window that appears:
(this will execute your file. Any syntax error will be reported to
If you cannot execute submit.pl
due to permissions errors, use
chmod 755 submit.pl
to set the correct permissions for
Executing the file 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
Try fetching the URL http://zee.cs.usna.edu/~mXXXXXX/Lab07/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):
Sometimes 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 executes 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: For this lab, you
are required to write and use at least one Perl function that receives
should have a file form.html from Lab02 (or later), copied into Lab07.
Your form should contain at least one element of the following input
types: text, password, checkbox, radio buttons, submit (your form will
likely contain more than that). Modify the form (in your Lab07 directory)
so that when you click the submit button, it invokes your new CGI
program. For testing, modify your
CGI program so that it reads in at least one value from your form and
displays the value in its resultant HTML output.
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):
For your first (or only) text field, ensure it
is filled out (not empty)
For your first (or only) set of checkboxes,
ensure at least one checkbox is selected. See the "Hints" section for
a discussion about checkboxes.
For your first (or only) set of radio buttons,
ensure at least one radio button is selected.
At least one of your checks must involve a
pattern match using regular expressions ? 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 valid 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 and only 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 in your Perl script.
final step: create three links in your top-level default.htm page
under the heading ?Lab07?
Under the name ?Form?, make a link to your
Under 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 hitting
Under the name ?LOG.txt? make a link to your log
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 "Lab07" (without the quotes) on the W drive. Your
instructor will assume that your web pages are viewable at
http://zee.cs.usna.edu/~mXXXXXX/Lab07/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 of your submit.pl file.
- A screen-shot of your
browser window showing the confirmation message you displayed after a
user submitted a form that passed the validity checks.
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 message to the browser.