use strict;
use Carp;

sub readin_dir
{
    my ( $filenames, $paths, $ext ) = @_;
    if ( ref($filenames) ne 'ARRAY' or ref($paths) ne 'ARRAY' or @$paths == 0 ) {
        carp( "readin_dir call lacks array_ref(s) for file names and/or paths\n" );
        return;
    }
    for my $path ( @$paths ) {
        $path =~ s{/+$}{};   # don't need or want trailing slash(es)
        opendir( my $dh, $path )
            or do { warn "readin_dir: open failed for $path\n"; next };

        my @subdirs = ();
        while ( my $file = readdir( $dh )) {
            next if ( $file =~ /^\.{1,2}$/ );
            if ( -d "$path/$file" ) {
                push @subdirs, "$path/$file";
            }
            elsif ( $ext eq '' or $file =~ /\.$ext$/ ) {
                push @$filenames, "$path/$file";
            }
        }
        closedir( $dh );
        readin_dir( $filenames, \@subdirs, $ext ) if ( @subdirs );
    }
}