Another idea for you:
I think it is straightforward and "simple" in concept.

#!/usr/bin/perl
use strict;
use warnings;

my %mycorpus = (
    a => "<blah blah blah 
blah
title:#this is text I want 1#
blah blah blah",

    b => "blah
title:#this is text I do not want# blah
title:#this is text I want 2#
blah
title:#this is text I do not want#
blah",

    c => "blah blah
title:#this is text I want 3#
title:#this is text I do not want#
title:#this is text I do not want#
title:#this is text I do not want#
blah",
);


foreach my $filename (sort keys %mycorpus) 
{
   foreach my $line (split /\n/,$mycorpus{$filename})
   {
       if ($line =~ /^title:#(.*)#\s*$/)
       {
           print "$line\n";
           last;
       }
   }
}

__END__
title:#this is text I want 1#
title:#this is text I want 2#
title:#this is text I want 3#
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