def get_verbose_flag(verbose):
    """Return verbose flag ' -v' if verbose=True, and empty string otherwise,
       for programs executed as shell commands.

    Parameters
    ----------
    verbose: bool
        Verbose mode

    Returns
    -------
    verbose_flag: string
        Verbose flag for shell command
    """
    if verbose is True:
        verbose_flag = ' -v'
    else:
        verbose_flag = ''
    return verbose_flag
