my $str="Study Protocol Number NBXF317N2201"; 
my ($term) = $str =~ /Protocol (?:(?:No\.|Number)? )?([A-Z0-9]{12})/; 
print $term;

##</code><code>##

my $str="Study Protocol Number NBXF317N2201"; 
my ($term) = $str =~ /Protocol (?:(?:No\.?|Number) )?([A-Z0-9]{12})/; 
print $term;

##</code><code>##

use strict;
use warnings;
for my $str ( "Study Protocol Number NBXF317N2201", 
		"Study Protocol No. NBXF317N2201",
		"Study Protocol NBXF317N2201",
		"Study Protocol No NBXF317N2201" ) { 
		my ($term) = $str =~ /Protocol (?:No\. |No |Number |)([A-Z0-9]{12})/; 
		print "$term\n";
}