use strict;
use warnings;

include('test.pl') > 2 or die('Couldnt include important file!');

# This sub returns the number of bytes read
# or a negative number if there was an error...
sub include
{
  my $FILE = shift;
  -e $FILE or return -1;      # File doesn't exist
  -f $FILE or return -2;      # not a plain file
  my $SIZE = -s $FILE;
  $SIZE > 2 or return $SIZE;  # File is basically empty
  my $CONTENT; my $F;
  open $F, '<:raw', $FILE or return -3;  # Can't open file
  binmode $F;
  sysread($F, $CONTENT, $SIZE) == $SIZE or return -4;  # Can't read
  close $F;
  eval($CONTENT);
  return $SIZE;
}

ShowMessage();
ChangeMessage('Whats up!');
ShowMessage();
exit;