my $var = 'LR20SR37PD30LR23CR23BT01H';
$var .= ' ' x 40 - length($var);

##</code><code>##

my $var = 'LR20SR37PD30LR23CR23BT01H';
$var = substr($var . ' ' x 40, 0, 40);

##</code><code>##

my $var = 'LR20SR37PD30LR23CR23BT01H';
$var = sprintf '%-40s', $var;