while(<DATA>) {
   if (m/\w{1,12}\s+(\d{1,5})\s+[a-zA-Z]{4}/) {
      my $site = $1;
      print "$site\n";
   }
}

__DATA__
BC001593 91 NPSL
BC001593 260 NASS
BC001593 293 NAST

# the output 
91
263
293