use strict;
use warnings;

my @lines = ("https://www.sec.gov/Archives/edgar/data/831001/000095010323011632/0000950103-23-011632.txt\n",
             "<FILENAME>dp198076_424b2-us2342673.htmSomeCrap\n",
             "<FILENAME>dp198076_424b2-us2342673.htm\n",
             "<FILENAME>dp198076_exfilingfees.htm\n",
            );

foreach my $line (@lines) {
  if (my ($doc_title) = $line=~ m/<FILENAME>(.*\.htm)\b/) {    
     print "Filename is $doc_title\n";
     last;  ############### this stops
     }
}

__END__
Filename is dp198076_424b2-us2342673.htm