my @target_files;
    my ( $imode, $omode );
    opendir DIR, $dir or warn "Cannot open $dir $!";
    if ( $cmd eq 'gzip' ) {
        @target_files = grep { !/\.gz$/ and -f "$dir/$_" } readdir DIR;
        $imode = "<";
        $omode = ">:gzip";
    }
    else {
        @target_files = grep /.\.gz$/, readdir DIR;
        $imode = "<:gzip";
        $omode = ">";
    }
    closedir DIR;

    for my $ifile ( @target_files ) {
        my $ofile;
        if ( $cmd eq 'gzip' ) {
            $ofile .= ".gz";
        } else {
            $ofile =~ s/\.gz$//;
        }
        open( I, $imode, $ifile ) or die "$ifile: $!";
        open( O, $omode, $ofile ) or die "$ofile: $!";
        while(<I>) { print O }
        close I;
        close O;
        unlink $ifile;
     }