A grep on the data to check for four spaces followed by a digit at the beginning of each line works:

use strict;
use warnings;
use List::MoreUtils qw/natatime/;

my $it = natatime 5, grep /\A\s{4}\d/, <DATA>;

while ( chomp( my @lines = $it->() ) ) {
    my $letter = 'A';
    my $acctNum = do { $lines[0] =~ /\s+(\d+)\s+(\d+)/; $1 . $2 };
    push @lines, " acctnum=$acctNum";
    
    print for map { s/\s+/$letter++ . ' '/e; "$_\n" } @lines;
}

__DATA__
Place your data here...

[download]

In reply to Re^7: raw data formatting by Kenosis
in thread raw data formatting by teamassociated

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.