use strict;
use warnings;
use Cwd;
use File::Find;

# Return a list of the absolute path of all plain .txt files under $dir
sub FindTextFiles
{
   my $dir = shift;
   my @files;
   # Note: -f = plain file (perldoc -f -X for doco of all file tests)
   find( { no_chdir => 1,
           wanted   => sub { -f && /\.txt$/ and push @files, $File::Find::name }
         },
         $dir
   );
   return @files;
}

my $dir = getcwd();
my @txtfiles = FindTextFiles($dir);
print "Found ", scalar(@txtfiles), " text files under dir '$dir'...\n";
for my $file (@txtfiles) {
   print "file='$file'\n";
   # could add code to modify the found files here ...
}