A simple approach is to loop through the lines and start a new record each time a primary key is detected: 
my %record;
my $item;
while (my $line = <DATA>) {
   chomp $line;
   if ($line =~ /^(\d+) (.*)$/) {
      $item = $1;
      $record{ $item} = " $2";
   }
   else {
      $record{ $item} .= $line;
   }
}

foreach my $item (keys %record) {
   print "$item $record{ $item}\n";
}

__DATA__
1000001 01.11.199600.00.00001 A1 1 SN Y
2001.11.200400098.0500073.5500083.35
5001.11.1997Professional attendance being an attendance at
5001.11.1997other than consulting rooms
1000002 01.11.199600.00.00001 A1 1 SN Y
2001.11.200400098.0500073.5500083.35
5001.11.1997Professional attendance being an attendance at
5001.11.1997consulting rooms

[download]

-Mark

In reply to Re: Format multiline to single line records by kvale
in thread Format multiline to single line records by kerrya

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.