CGI Programming with Perl

CGI Programming with `Perl`

A survey Example

Opinion surveys of users of the web document

Each user fills in the choices

The collective data must be stored between visits

Where? in the server disk!!

For instance the cgi-bin directory

Major problem:

More than one user may submit survey forms at the same time ==> Corruption of data

Require that the access to the file be by only one user at a time ==> locking the file

The Perl function flock can be used to lock/unlock the file
- The first parameter of flock is the filehandle of the file to be locked/unlocked
- The second parameter is the specified process lock (2) or unlock(8)
```
$LOCK = 2;
$UNLOCK =8;
...
flock(<TAX_DATA>, $LOCK);  # Locking acces to the file
chomp($taxes = <TAX_DATA>);
#
# Processing of $taxes
#
flock(<TAX_DATA>, $UNLOCK);  # unlocking acces to the file
```

The survey form collects info on a particular items

The user can fill-in information or ask to see the current results

<!DOCTYPE html PUBLIC "-//w3c//DTD XHTML 1.0 Strict//EN"
  "http://www.w3.org/TR/xhtml1/DTD/xhtml-strict.dtd">

<!-- conelec.html 
     A document to present the user with a consumer electronics 
     purchasing survey form 
     -->

<html>
<head>
<title> Consumer Electronics Purchasing Survey </title>
</head>
<body>
<form action = "http://www.cs.ucp.edu/cgi-bin/sebesta/conelec1.pl" 
      method = "POST">
<h2> Welcome to the Consumer Electronics Purchasing Survey </h2>
<br />

<h4> Your Age Category: </h4>
<input type = "radio"  name = "age"  value = "b1025"  checked > 10-25 <br />

<input type = "radio"  name = "age"  value = "b2640"> 26-40 <br />
<input type = "radio"  name = "age"  value = "b4160"> 41-60 <br />
<input type = "radio"  name = "age"  value = "o60"> Over 60 <br /> <br />

<h4> Your Gender: </h4>
<input type = "radio"  name = "gender"  value = "female"  checked> Female <
br />
<input type = "radio"  name = "gender"  value = "male"> Male <br /> <br />

<h4> Your Next Consumer Electronics Purchase will be: </h4>
<input type = "radio"  name = "vote"  value = "0"> Conventional TV <br />
<input type = "radio"  name = "vote"  value = "1"> HDTV <br />
<input type = "radio"  name = "vote"  value = "2"> VCR <br />
<input type = "radio"  name = "vote"  value = "3"> CD player <br />
<input type = "radio"  name = "vote"  value = "4"> Mini CD player/recorder 
<br />
<input type = "radio"  name = "vote"  value = "5"> DIVD player <br />
<input type = "radio"  name = "vote"  value ="6"  checked> Other <br /> <br /
>

<input type = "submit"  value = "Submit Order">
<input type = "reset"  value = "Clear Order Form">

</form>

<hr/>
To see the results of the survey so far, click 
        <a href = "http://www.cs.ucp.edu/cgi-bin/sebesta/conelec2.pl"> here
 </a>;
</body>
</html>

The writing of the CGI files:

Collecting the information

The format for the file to store the data
- eight strings that represent the rows of voting totals
- The first four rows store the votes of female visitors,
- The next four rows store the votes of male visitors,
- The file needs to be created and initialized before use
- each line should have a string of seven zeros separated by spaces
  
  On a CGI when open fails, die can not be used
  
  Create an error function that returns a message to the user

The CGI program to record and collect the information:

Decode the data from the query string

Determine which row of the file must be modified

Open, lock, read, unlock, and close the survey data file

Split the affected data string into numbers and store them in an array

Modify the affected array element and join the array back into the string

Open, lock, write, unlock, and close the survey data file

# conelec1.pl
# This CGI program processes the consumer electronics survey
#  form and updates the file that stores the survey
#  and updates the file that stores the survey data,

use CGI qw(:standard);

# error - a function to produce an error message for the client
#         and exit in case of open errors

sub error {
    print "Error - file could not be opened in conelec1.pl <br />";
    print end_html();
    exit(1);
}

# Begin main program
# Get the form values

my($age, $gender, $vote) = (param("age"), param("gender"),
        param("vote"));

# Produce the header for the reply page - do it here so
#  error messages appear on the page

print header();

# Set names for file locking and unlocking

$LOCK = 2;
$UNLOCK = 8;

# Set $index to the line index of the current vote

$index = 0;
if ($gender eq "male") {
    $index = 4;
}
if ($age eq "b2640") { $index += 1 }
elsif ($age eq "b4160") { $index += 2 }
elsif ($age eq "o60") { $index += 3 }

# Open and lock the survey data file

open(SURVDAT, "<survdat.dat") or error();
flock(SURVDAT, $LOCK);

# Read the survey data file, unlock it, and close it

for ($count = 0; $count <= 7; $count++) {
   chomp($file_lines[$count] = <SURVDAT>);
}

flock(SURVDAT, $UNLOCK);
close(SURVDAT);

# Split the line into its parts, increment the chosen
# device, and put it back together again

@file_votes = split / /, $file_lines[$index];
$file_votes[$vote]++;
$file_lines[$index] = join(" ", @file_votes);

# Reopen the survey data file for writing and lock it

open(SURVDAT, ">survdat.dat") or error();
flock(SURVEY, $LOCK);

# Write out the file data, unlock the file, and close it

for ($count = 0; $count <= 7; $count++) {
    $line = $file_lines[$count];
    print SURVDAT "$line\n";
}

flock(SURVDAT, $UNLOCK);
close(SURVDAT);

# Build the web page to thank the survey participant

print start_html("Thankyou"),
print "Thanks for participating in our survey <br /><br />\n";
print end_html();

The reporting procedure

There are 56 categories => a table is best

Functions, table, caption, Tr, th, and td are used.

Functions Tr, th, and td require addresses as parameters

To pass a literal list, it must be bracketed

To pass an array , it must be backslashed in the actual parameters

# EZ table.pl
table({-border => "border"},
      caption("Sales Figures"),
      Tr(
         [tr(["Salesperson", "Mon", "Tues", "Wed",
                 Thu","Fri"]),
          th("Mary").td(\@maysales),
          th("Freddie").td(\@freddiesales),
          th("Spot").td(\@spotsales),
         ]
        )
      );

The survey has the following tasks:

Open and lock data file, read lines into array of strings, then unlock and close the data file

Split the first four rows into arrays of votes for four age groups

Unshift row titles into the votes rows

Create column titles row with th and put its address in an array

Use td for each row of data

Push addresses of row votes onto the row address array

Create the table using Tr on an array of row addresses

Repeat last 6 steps for the last four rows of data

#!/usr/local/bin/perl -w

# conelec2.pl - display the survey results

use CGI qw(:standard);

# error - a function to produce an error message for the client
#         and exit in case of open errors

sub error {
    print "Error - file could not be opened in conelec2.pl <br/>";
    print end_html();
    exit(1);
}

# Begin main program
# Initialize file locking/unlocking parameter

$LOCK = 2;
$UNLOCK = 8;

print header();

# Open, lock, read, and unlock the survey data file

open(SURVDAT, "<survdat.dat") or error();
flock(SURVDAT, $LOCK);
@vote_data = <SURVDAT>;
flock(SURVDAT, $UNLOCK);

# Create the beginning of the result web page

print start_html("Survey Results");
print "<h2> Results of the Consumer Electronics Purchasing Survey </h2><br/
> \n";

# Split the input lines for females into age arrays

@age1 = split(/ /, $vote_data[0]);
@age2 = split(/ /, $vote_data[1]);
@age3 = split(/ /, $vote_data[2]);
@age4 = split(/ /, $vote_data[3]);

# Add the row titles to the age arrays

unshift(@age1, "10-25");
unshift(@age2, "26-40");
unshift(@age3, "41-60");
unshift(@age4, "Over 60");

# Make the column titles array

@col_titles = ("Age Group", "Conventional TV", "HDTV", "VCR",
               "CD player", "MiniCD player/recorder", "DIVD player",
               "Other");

# Create the column titles in HTML by giving their address to the th
#  function and storing the return value in the @rows array

@rows = th(\@col_titles);

# Now create the data rows with the td function
#  and add them to the row addresses array

push(@rows, td(\@age1), td(\@age2), td(\@age3), td(\@age4));

# Create the table for the female survey results
#  The address of the array of row addresses is passed to Tr

print table({-border => "border"},
            caption("<h3>Survey Data for Females</h3>"),
             Tr(\@rows)
           );

# Split the input lines for the males into age arrays

@age1 = split(/ /, $vote_data[4]);
@age2 = split(/ /, $vote_data[5]);
@age3 = split(/ /, $vote_data[6]);
@age4 = split(/ /, $vote_data[7]);

# Add the first column titles to the rows of color votes

unshift(@age1, "10-25");
unshift(@age2, "26-40");
unshift(@age3, "41-60");
unshift(@age4, "Over 60");

# Create the column titles in HTML by giving their address to the th
#  function and storing the return value in the @rows array

@rows = th(\@col_titles);

# Now create the data rows with the td function
#  and add them to the row addresses array

push(@rows, td(\@age1), td(\@age2), td(\@age3), td(\@age4));

# Create the table for the female survey results
#  The address of the array of row addresses is passed to Trsults

print "<br/><br/>";
print table({-border=>undef},
            caption("<h3>Survey Data for Males</h3>"),
            Tr(\@rows)
           );

print end_html();