use warnings;
use strict;

opendir my $dh, $ARGV[0] or die "can't open directory: $!";
while ( readdir $dh ) {
    chomp;
    next if $_ eq '.' or $_ eq '..';
    #..... get each file to work on ....
}
closedir $dh or die "can't close directory: $!";

### or use File::Find like so:

use File::Find qw(find);
find( sub { print $_, $/ }, $ARGV[0] );