def generate_blastdb_commands(filenames, outdir, blastdb_exe=None, mode="ANIb"):
    """Return a list of makeblastdb command-lines for ANIb/ANIblastall

    - filenames - a list of paths to input FASTA files
    - outdir - path to output directory
    - blastdb_exe - path to the makeblastdb executable
    """
    if mode == "ANIb":
        construct_db_cmdline = construct_makeblastdb_cmd
    else:
        construct_db_cmdline = construct_formatdb_cmd
    if blastdb_exe is None:
        cmdlines = [construct_db_cmdline(fname, outdir) for fname in filenames]
    else:
        cmdlines = [
            construct_db_cmdline(fname, outdir, blastdb_exe) for fname in filenames
        ]
    return cmdlines