def coverage(args):
    """
    %prog coverage *.coverage

    Plot coverage along chromosome. The coverage file can be generated with:
    $ samtools depth a.bam > a.coverage

    The plot is a simple line plot using matplotlib.
    """
    from jcvi.graphics.base import savefig

    p = OptionParser(coverage.__doc__)
    opts, args, iopts = p.set_image_options(args, format="png")

    if len(args) != 1:
        sys.exit(not p.print_help())

    covfile, = args
    df = pd.read_csv(covfile, sep='\t', names=["Ref", "Position", "Depth"])

    xlabel, ylabel = "Position", "Depth"
    df.plot(xlabel, ylabel, color='g')

    image_name = covfile + "." + iopts.format
    savefig(image_name)