There are many ways to accomplish this. Here's one (untested):

#!/usr/bin/perl -wT
use strict;
use CGI qw/:standard/;

my %errors;
my ( $candidate ) = ( param( 'candidate' ) =~ /^([\s\w]+)$/ );

# candidate must be defined and have at least one non-whitespace chara
+cter
if ( ! defined $candidate or $candidate !~ /\S/ ) {
    $errors{ candidate } = 'You must supply a value for candidate';
}

# grab more params and untaint

if ( %errors ) {
    display_page_with_errors( \%errors );
}
[download]

Cheers,
Ovid

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