sub has_vertical_bar {
  my ($string) = @_;
  return $string =~ /\|/;
};

# ... later, in your code ...
my @parameters = qw(name site siteid email pass aim yahoo icq msn location intrests );
my $errormsg = "";
foreach my $parameter (@parameters) {
  if has_vertical_bar($q->param($parameter)) {
    $errormsg ||= "There was some problem with your input. Please make sure no fields have vertical bars.";
    $errormsg .= "I found a vertical bar in the field $parameter. ";
  };
};

error($errormsg) if ($errormsg);