• html_row: This subroutine should return a string that holds an HTML table row given an array. The row should have one cell for each element of the array passed in as parameters. For example, the call:

  $foo = html_row(3,"HI",17);

  should produce something like this (this would be the value of $foo after the call):

  "<TR> <TD>3</TD> <TD>HI</TD> <TD>17</TD></TR>"
  

  NOTES:

  • You don't know how many parameters are being passed, so you need to loop over the elements in @_.
  • You need to create a string that holds the result, don't print it out!
  • Remember the string concatenation operator "."
  • You can find out the length of a perl array by assigning the array to a scalar variable. For example, to find out the length of the array named @blah you could do this: $length = @blah;. Now the variable $length is the number of elements in the array.

• html_table: This subroutine should return a string that holds an HTML table given an array. The subroutine should assume that each parameter passed in is an HTML table row (just like one constructed by the html_row subroutine).

  So if the following call is made:

  $blah = html_table("<TR><TD>HI</TD><TD>Dave</TD></TR>",
                          "<TR><TD>33</TD><TD>17</TD></TR>");
  

  The resulting value of $blah should be something like this:

  "<TABLE>
  <TR><TD>HI</TD><TD>Dave</TD></TR>
  <TR><TD>33</TD><TD>17</TD></TR>
  </TABLE>"
  

  NOTES:

  • Newlines are not important in HTML
  • All you need to do is paste the strings together and add in the start and end tags for TABLE.
  • Don't print it out - just return the string!

Testing your subroutines: The following code can be used to test your subroutines. Just include this code in your file as the main program.

# generate an HTML table of the powers of 2

for ($i=0;$i<10;$i++) {
    $rows[$i] = html_row($i,2**$i);
}

$table = html_table(@rows);
print $table;

You can save the output of this perl program in a file, and then load the file into your browser to see what the result looks like. From the DOS prompt use the ">" redirection operator to send the output of the perl program to the file named ex12out.html:

C:\EIWFILES> perl ex12.pl > ex12out.html

2. Improved Tables

Now you should add an extra parameter to your subroutines to make it possible to generate tables with borders and background colors. You need to add 2 parameters to your html_table subroutine, the first parameter specifies the border width and the second paremeter specifies the background color. For example, the following call of html_table:

$foo = html_table(3,"blue",@rows);

should result in a table that has something like the following in the TABLE tag:

<TABLE BORDER=3 BGCOLOR="blue">

NOTES:

• In a perl subroutine all the parameters are available in the array @_, so you have to treat the first element $_[0] as the border width and the second element $_[1] as the color. The remaining elements of the array @_ are the rows of the table (as in the previous exercise). There are a couple of ways to handle this, here is a real easy way:

  # start of the subroutine html_table sub html_table { local($border,$color,@rows) = @_; ...

3. Improved Rows

Now add the background color to the html_row subroutine as well, so now the first parameter to html_row is the background color for the row. The attribute BGCOLOR goes in the TR tag just like in the TABLE tag.

Test your subroutines with this program:

# generate an HTML table of the powers of 2,3 and 4

$rows[0] = html_row("white"," n " , 
                              "nth power of 2",
                              "nth power of 3",
                              "nth power of 4");

for ($i=0;$i<10;$i++) {
    if ($i % 2) {
	$rows[$i+1] = html_row("#cccccc",$i,2**$i,3**$i,4**$i);
    } else {
	$rows[$i+1] = html_row("#ccccff",$i,2**$i,3**$i,4**$i);
    }
}
$table = html_table(1,"",@rows);
$table2 = html_table(0,"black",html_row("",$table));
print "Here are the powers of 2, 3 and 4<BR><BR>\n";
print $table2;

4. Turn it into a CGI program

Turn your perl program from part 3 into a CGI program. Since your program doesn't need any input, we can ignore any query string that is sent and just worry about what gets sent back to the browser. We just send output to the browser via STDOUT, and since print already does that, we don't need to change much in the program. The only necessary change is that a CGI program must send back a Content-Type: HTTP response header that indicates what kind of document is being sent. In this case we are sending back an HTML document, so you need to add the following to your perl program:

# send back header that says this is HTML:

print "Content-type: text/html\r\n\r\n";

NOTES:

• Remember that the header line must appear before any of the document content - so make sure the above print statement is before any other print statment in your program.
• The \r\n\r\n makes sure that the header line is followed by a CRLF pair (carrige-return, line-feed), and that there is a blank line following the header line.
• You need to install the program in the right place (or your web server won't be able to find it). You can put it in the cgi-bin directory, or (assuming you changed the CGI setup for your server the way we described in class), you can put it in any folder as long as the name of the file ends with ".cgi".