use strict;
use warnings;
$/ = undef;

my $data = <DATA>;
$data =~ s{^(.*?)\|}{sprintf '%-45s', $1}meg;
print $data;

__DATA__
ABCDEFGHIJKLMNOPQRST|1234
ABCDEFGHI|12345
ABCDE|1234
ABCDEFGHIJKL|123
ABCDEFG|123456
ABCDEFGHIJKLMNO|12