use strict    ;
use warnings  ;
use File::Find;
use Data::Dump;


my $dir = shift || die "Dir name missing as argument\n";

my @files = ();
find( \&wanted, "$dir" ); 
dd( \@files ) ;

exit() ;


sub wanted() {
    push @files, $File::Find::name if(/\.txt$/i); # .txt or whatever.
}