$c = "test test test";

$c = correct_length($c);

$fmt = "A4 x1 A4 x1 A4 x1 A4";
@c = unpack($fmt, "$c");
print join ("*",@c), "\n";

$d = "test test test ";
$d = correct_length($d);
$fmt = "A4 x1 A4 x1 A4 x1 A4";
@d = unpack($fmt, "$d");
print join ("*",@d), "\n";

sub correct_length {
    my ($string) = shift;
    $string .= ' ' unless length($string) >= 15;
    return($string);
}

##</code><code>##

my %formats = (
   "item_name"  => 15, # where 15 is the length
   "item_name2" => 20,
   # etc.
);

# code removed for demonstration

$c = correct_length($c,'item_name');

sub correct_length {
    my ($string,$item) = @_;
    $string .= ' ' unless length($string) >= $formats{$item};
    return($string);
}