def make_bed(df, columns="all", outname="filtered_bed"):
    """
    function converts input df to
    BED 6 file, and retuns filename

    paramenters:
    df=pandas df
    columns=list of target columns
    outname=BED filename
    """
    if columns != "all":
        bed_df = df[columns].copy()
    else:
        bed_df = df
    bed_df.to_csv(outname, sep="\t", header=False, index=False)

    return outname