First of all, when asking a question and then later on changing it, it would be nice if you mentioned the question has been updated or modified. That way people that replied to the original question won't look as though they're talking out of their *insert favorite bodypart here*.
As for the actual regex, you asked for all the data, so by that I assume you don't want to get rid of any html tags. I'll also assume you mean TRNsquare_thingy instead of the other way around...
use strict;
use warnings;
my $blurb = 'Starting the , text and there are more TEST BPR<b> PE 12.
+3AZ 2 3 4 anything, BPR set ? & @ TRN $ ?of characters Can be anythin
+g BPR* TRN# in here 7 9 something here 11 <b>TRN 1 14 15 16 17 18 P
+E 12.3AZ ST21st 37 17 18 PE 12.3AZ ST21st and so on and more text fol
+lows';
#035 is the octal for that squarethingy you got there...
$blurb =~ /\035BPR(.+)TRN\035/;
print "result: $1\n";
