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 TESTBPR<b>PE12.
+3AZ234anything, BPR set ? & @ TRN $ ?of charactersCan be anythin
+g BPR* TRN# in here79something here11<b>TRN1 1415161718P
+E12.3AZST21st371718PE12.3AZST21stand 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";
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