I see what you are trying to do here. The while ( <DATA> ) loop iterates through lines of the data file, and then you are creating more lines inside the loop that you want to iterate through them as if they were additional lines in the data file. Unfortunately, you would have to add them to the actual data file for that effect. To do what you want, you can add another loop to iterate through the new lines you've added:

!/usr/bin/perl

use strict;
use warnings;

my $title;
while ( <DATA> )
{ 
  chomp;

  if ( /\(\w+\-\d+\)$/ )
    { $title = $_; }
  else
  { 
    s/(?:^|\s)(\d\-\d\w{2}(?:\.\w+)?|[A-Z]\d{2}(?:\.\d+)?)/\n$1/g;
    foreach my $line ( split ( "\n" ) )
    { 
      next if $line !~ /^(\d\-\d\w{2}(?:\.\w+)?|[A-Z]\d{2}(?:\.\d+)?)/
+;
      print "$title;$line\n";
    }
  }
}

__DATA__
Titel Text (A12-3)
3-123.7 Just another text 3-123.8 Some more text
A12.34 Another item B56.78 Yet another item
Another Titel Text (B23-9)
1-22a.b Just another text
2-3cd.e Some more text
W12.34 Another item
Z56.78 Yet another item
Some trash
Some trash

[download]

Output:

Titel Text (A12-3);3-123.7 Just another text
Titel Text (A12-3);3-123.8 Some more text
Titel Text (A12-3);A12.34 Another item
Titel Text (A12-3);B56.78 Yet another item
Another Titel Text (B23-9);1-22a.b Just another text
Another Titel Text (B23-9);2-3cd.e Some more text
Another Titel Text (B23-9);W12.34 Another item
Another Titel Text (B23-9);Z56.78 Yet another item

[download]
Arnon Weinberg Back2Front - The Web Site People

In reply to Re: Insert newline by thewebsi
in thread Insert newline by Anonymous Monk

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.