FIT3084: Perl Programming


In the previous lecture:

In this lecture:


References:


Perl at light speed




Datatypes & Variables





Input and Output


Expressions


Functions / Subroutines

Functions are declared and called as illustrated by this simple example.

#!/usr/monash/bin/perl -w
$val1 = 7;
$val2 = 9;

$answer = &maximum($val1, $val2);      # assign global $answer to maximum of 9 and 7
                                       # use the '&' symbol to call a function
print "answer = $answer\n";            # print the value of $answer

sub maximum                            # define a subroutine maximum
{
        my ($arg1, $arg2) = @_;        # receive the arguments passed in through @_
                                       # and place them in the local variables $arg1 & 2
        
        my ($result);                  # declare a local variable $result

        if ($arg1 >= $arg2)
        { $result = $arg1; }

        else
        { $result = $arg2; }

        return $result;                # return $result
}


A more complex example (from the Camel book):

Suppose we have a list of student names and their assignment scores:

Noel 25
Ben 76
Clementine 49
Norm 66
Chris 92
Doug 42
Carol 25
Ben 12
Clementine 0
Norm 66
Ben 9

 

Consider the following Perl program:

#!/usr/monash/bin/perl -w
open (GRADES, "grades") or die "Can't open grades: $!\n";

while ($line = <GRADES>) {
	($student, $grade) = split(" ", $line);
	$grades{$student} .= $grade . " ";
}

foreach $student (sort keys %grades) {
	$scores = 0;
	$total = 0;
	@grades = split(" ", $grades{$student});
	foreach $grade (@grades) {
		$total += $grade;
		$scores++;
	}
	$average = $total / $scores;
	print "$student: $grades{$student}\tAverage: $average\n";
}

Run the program on your local account and look at the results. Modify the script so the results are displayed on a web page via CGI.


CGI.pm

Example:

#!/usr/monash/bin/perl

use CGI qw(:standard);

print header;
print start_html('A Simple Example'),
    h1('A Simple Example'),
    start_form,
    "What's your name? ",textfield('name'),
    p,
    "What's the combination?",
    p,
    checkbox_group(-name=>'words',
                   -values=>['eenie':'meenie','minie','moe'],
                   -defaults=>['eenie':'minie']),
    p,
    "What's your favorite color? ",
    popup_menu(-name=>'color',
               -values=>['red':'green','blue','chartreuse']),
    p,
    submit,
    end_form,
    hr;

if (param()) {
    print 
        "Your name is",em(param('name')),
        p,
        "The keywords are: ",em(join(", ",param('words'))),
        p,
        "Your favorite color is ",em(param('color')),
        hr;
}
print end_html;

 

#!/usr/local/bin/perl
use CGI qw/:standard/;
print header(),
start_html(-title=>'Wow!'),
h1('Wow!'),
'Look Ma, no hands!',
end_html();
This code uses the cgi module in "function style" where its routines are brought into the standard namespace.

 

#!/usr/local/bin/perl
use CGI;
$q = new CGI;
print $q->header(),
$q->start_html(-title=>'Wow!'),
$q->h1('Wow!'),
'Look Ma, no hands!',
$q->end_html();
This code uses the cgi module in "object oriented style" where its routines are accessed through an "object" (CGI).

 

 

 

For more information see: http://stein.cshl.org/WWW/CGI/.


Where to find more:

This Page of Perl Pearls is only the bare minimum required to understand the examples given in lectures.


Please read a book or website on Perl to become more familiar with the language. Above all, practice writing a few Perl scripts!

Perl web sites:



This lecture's key point(s):


Courseware | Lecture notes

©Copyright Alan Dorin 2008