my @files;

#reading directory
opendir(MYDIR, "data");
my @contents = readdir MYDIR;

#going through all files in directory
foreach my $file(@contents) {

   #if file is a .txt
   if($file =~ m/\.txt$/) {

      #store file to array
      push(@files, $file);
   }
}

#closing directory handle
closedir MYDIR;