#! /usr/bin/perl -wT
use strict;
use CGI qw( :standard );
my $testvalue = '';

printForm();
if ( param() ) 
{ 
   br();
   $testvalue = param( 'TestValue' );
   my $errors = "";
   $errors .= paramCheck( "Test Value", $testvalue, 1, 30, 
                          '/\W/', "letters and numbers" );      
   if ( $errors )
      { print p( "Failed" ), "<UL>$errors</UL>" }
   else
      { print p( "Passed...wow, what a surprise." ); }
}
exit 1;

sub paramCheck
# Returns "" if no error or description of problem(s).
{
  my $lbl = shift;  # Field name for error messages
  my $val = shift;  # Value received from the CGI query
  my $min = shift;  # Minimun length; Use >0 for required fields
  my $max = shift;  # Maximum allowed length
  my $pat = shift;  # Regex to validate the data against.
  my $msg = shift;  # Explanation added to error if Regex fails.
  my $err = "";     # Holds error message
  my $len = length( $val );

  if ( $min ) # <> 0
  {
     if ( $len < $min )
     { $err .= wes( "$lbl cannot be blank." ); }
  }
  elsif ( $len > $max ) 
  { 
     my $s = $len == 1 ? "" : "s";
     $err .= wes( "$lbl is currently $len character$s; " . 
                  "; it can only be $max character$s long." );
  }
  else
  {
    unless ( $val =~ $pat )
    { 
      $err .= wes( "$lbl contains invalid characters; " . 
                   "it can only hold $msg." );
    }
  }
  return $err;
}

sub printForm
{
   print header(), 
         start_html( -title => 'Test' );
   print start_form( "post", 
                     "/cgi-bin/valtest.cgi",
                     "application/x-www-form-urlencoded" );
   print p( 'Enter a value:' ),
         textfield( 'TestValue', $testvalue, '40', '30' );
   print br(), submit( "Try it" ), 
         '&nbsp;&nbsp;',
         reset( "Reset" );
   print end_form();
   print end_html();
}

sub wes
# Wrap an Error String with desired tags.
{
   my $input = shift;
   return "<LI>" . $input . "</LI>";
}