CGI Programming

The final version of the program, with (a) required fields, (b) full-English descriptions of those fields, and (c) a better error message when we cannot open the file, reads as follows:

#!/usr/local/bin/perl5
# We want to use the CGI module
use CGI;
# Set the filename to which we want the elements
# saved
my $filename = "/tmp/formcontents";
# Set the character that will separate fields in
# the file
my $separation_character = "\t";
# In what order do we want to print fields?
my @fields = ("name",
              "email",
              "address",
              "country",
              "sex");
# Which fields are required?
my @required_fields = ("name",
                       "email",
                       "address");
# What is the full name for each required field?
$FULLNAME{"name"} = "your full name";
$FULLNAME{"email"} = "your e-mail address";
$FULLNAME{"address"} = "your mailing address";
# Create a new CGI object
my $query = new CGI;
# ---------------------------------------------
# Make sure that all required fields have arrived
foreach $field (@required_fields)
{
    # Add the name of each missing field
    push (@missing_fields, $field)
    if ($query->param($field) !~ m/\w/);
}
# If any fields are missing, invoke the error
# routine
&missing_field(@missing_fields)
  if @missing_fields;
# ---------------------------------------------
# Open the file for appending
  open (FILE, "7gt;>$filename") ||
  &error_opening_file($filename);
# Grab the elements of the HTML form
@names = $query->param;
# Iterate through each element from the form,
# writing each element to $filename. Separate
# elements with $separation_character defined
# above.
foreach $index (0 .. $#fields)
{
    # Get the input from the appropriate HTML
    # form element
    $input = $query->param($fields[$index]);
    # Remove any instances of
    # $separation_character
    $input =~ s/$separation_character//g;
    # Now add the input to the file
    print FILE $input;
    # Don't print the separation character after
    # the final element
    print FILE $separation_character if
    ($index < $#fields);
}
# Print a newline after this user's entry
print FILE "\n";
# Close the file
close (FILE);
# ---------------------------------------------
# Now thank the user for submitting their
# information
# Print an a appropriate MIME header
print $query->header("text/html");
# Print a title for the page
print $query->start_html(-title=>"Thank you");
# Print all of the name-value pairs
print "<P>Thank you for submitting ";
print "the form.</P>\n";
print "<P>Your information has been ";
print "saved to disk.</P>\n";
# Finish up the HTML
print $query->end_html;
# ---------------------------------------------
# Subroutines
sub missing_field
{
    # Get our local variables
    my (@missing_fields) = @_;
    # Print an a appropriate MIME header
    print $query->header("text/html");
    # Print a title for the page
    print $query->start_html(-title=>
    "Missing field(s)");
    print "<P>You are missing the following
    required fields:</P>\0";
    print "<ul>\n";
    # Iterate through the missing fields,
    # printing them
    foreach $field (@missing_fields)
    {
        print "<li> $FULLNAME{$field}\n";
    }

    print "</ul>\n";

    print "</ul>\n";

    # Finish up the HTML
    print $query->end_html;

    exit;
}
sub error_opening_file
    {
        my ($filename) = @_;
        # Print an a appropriate MIME header
        print $query->header("text/html");
        # Print a title for the page
        print $query->start_html(-title=>
        "Error opening file");
        # Print the error
        print "Could not open the file
        \"$filename\".</P>\n";
        # Finish up the HTML
        print $query->end_html;
        exit;
    }

One of the most common CGI applications on the Web is a “guest-book”, which allows visitors to a site to sign in, leaving their names, e-mail addresses and short notes. We can easily construct such a program, using the basic framework seen in the above programs. The only difference between the “guestbook” program and the programs we have seen so far is that the guest-book must be formatted in HTML in order for users to be able to read it in their browsers.

Here is a very simple guest-book program that is virtually the same as the previous program we saw:

<HTML>
<Head>
<Title>Guestbook entry</Title>
</Head>
<Body>
<H1>Guestbook entry</H1>
<Form action="/cgi-bin/guestbook.pl"
    method=POST>
<P>Name: <input type=text name="name"
    value=""></P>
<P>E-mail address: <input type=text name="email"
value=""></P>
<input type=submit>
</Form>
</Body>
</HTML>

The following program is the same as the one above, except that it saves data to the “guestbook.html” and formats the data in HTML.

#!/usr/local/bin/perl5
# We want to use the CGI module
use CGI;
# Set the filename to which we want the elements
# saved
my $filename =
"/home/reuven/Consulting/guestbook.html";
# Set the character that will separate fields in
# the file
my $separation_character = "</P><P>";
# In what order do we want to print fields?
my @fields = ("name", "email");
# Which fields are required?
my @required_fields = ("name", "email");
# What is the full name for each required
# field?
$FULLNAME{"name"} = "your full name";
$FULLNAME{"email"} = "your e-mail address";
# Create a new CGI object
my $query = new CGI;
# ---------------------------------------------
# Make sure that all required fields have arrived
foreach $field (@required_fields)
{
  # Add the name of each missing field
  push (@missing_fields, $field) if
  ($query->param($field) !~ m/\w/);
}
# If any fields are missing, invoke the error
# routine
&missing_field(@missing_fields) if
  @missing_fields;
# ----------------------------------------------
# Open the file for appending
open (FILE, ">>$filename") ||
  &error_opening_file($filename);
# Grab the elements of the HTML form
@names = $query->param;
# Iterate through each element from the form,
# writing each element to $filename. Separate
# elements with $separation_character defined
# above.
foreach $index (0 .. $#fields)
{
  # Get the input from the appropriate HTML form
  # element
  $input = $query->param($fields[$index]);
  # Remove any instances of $separation_character
  $input =~ s/$separation_character//g;
  # Now add the input to the file
  print FILE $input;
  # Don't print the separation character after the
  # final element
  print FILE $separation_character if
  ($index < $#fields);
}
# Print a newline after this user's entry
print FILE "<BR><HR><P>\n\n";
# Close the file
close (FILE);
# -------------------------------------------
# Now thank the user for submitting his
# information
# Print an a appropriate MIME header
print $query->header("text/html");
# Print a title for the page
print $query->start_html(-title=>"Thank you");
# Print all of the name-value pairs
print "<P>Thank you for submitting ";
print "the form.</P>\n";
print "<P>Your information has been ";
print "saved to disk.</P>\n";
# Finish up the HTML
print $query->end_html;
# --------------------------------------------
# Subroutines
sub missing_field
{
  # Get our local variables
  my (@missing_fields) = @_;
  # Print an a appropriate MIME header
  print $query->header("text/html");
  # Print a title for the page
  print $query->start_html(-title=>"
  Missing field(s)");
  print "<P>You are missing the ";
  print "following required fields:</P>\n";
  print "<ul>\n";
  # Iterate through the missing fields, printing
  # them
  foreach $field (@missing_fields)
    {
        print "<li> $FULLNAME{$field}\n";
        }
  print "</ul>\n";
  print "</ul>\n";
  # Finish up the HTML
  print $query->end_html;
  exit;
}
sub error_opening_file
{
  my ($filename) = @_;
  # Print an a appropriate MIME header
  print $query->header("text/html");
  # Print a title for the page
  print $query->start_html(-title=>
  "Error opening file");
  # Print the error
  print "Could not open the ";
  print "file \"$filename\".</P>\n";
  # Finish up the HTML
  print $query->end_html;
  exit;
}

The above program will take input from the HTML form and save the data in an HTML-formatted file. If that file is accessible from the web server, your users should be able to view others' entries in the guest-book.