Assuming you want the best solution to the problem then the way to parse a data file that contains records separated by some delimiter ie two newlines (aka a blank line) is to set the input record separator to that delimiter and then read the data in one record at a time. For example in your case you could parse the data into a hash like this: 

#!/usr/bin/perl
local $/ = "\n\n";
while(<DATA>) {
    next unless m/U\d+/;
    chomp;
    chomp(my $text = <DATA>);
    $h{$_} = $text;
}
use Data::Dumper;
print Dumper \%h;
__DATA__
U448.1

Several walls of the imperial city of Constantinople which had been fr
+eshly
rebuilt with masonry, and fifty-seven towers collapsed as a result of 
+a
violent earthquake which prevailed in various places.

U483.2

Or, this year the battle of Ocha according to others, won by Muirchert
+ach
Mac Erca and by Fergus Cerball son of Conall of Cremthann, and by Fiac
+hra
Lon son of the king of Dal nAraide.

[download]

An inefficient regex solution is: 

my $str = join '', <DATA>;
%bits = $str =~ m/^(U[\d\.]+)\n\n(.*?)\n\n/msg;
use Data::Dumper;
print Dumper \%bits;
__DATA__
[snip]

[download]

You need .*? /m /s and /g to make it work and it is not efficient due to backtracking. See perlre

cheers

tachyon

In reply to Re: Regex Question by tachyon
in thread Regex Question by cyocum

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.