set_hostname.py

#!/usr/bin/env python

from optparse import OptionParser
from subprocess import check_call


def main():
    parser = OptionParser("usage: %prog [options] fqdn")
    parser.add_option("-d", "--dry-run",
            action="store_true", dest="dry_run")
    (options, args) = parser.parse_args()
    if len(args) != 1:
        parser.error("incorrect number of arguments")
    fqdn = args[0]
    host = fqdn.split(".")[0]
    hostsfile = "/etc/hosts"

    with open(hostsfile, "r") as f:
        hosts = f.readlines()

    if options.dry_run:
        hostsfile = "/dev/stdout"

    with open(hostsfile, "w") as f:
        for line in hosts:
            split = line.split()
            if len(split) == 0 or split[0] != "127.0.1.1":
                f.write(line)
        f.write("127.0.1.1 {fqdn} {host}\n".format(host=host, fqdn=fqdn))

    if options.dry_run:
        return

    with open("/etc/hostname", "w") as f:
        f.write("{host}\n".format(host=host))

    check_call(["hostname", "-F", "/etc/hostname"])


if __name__ == "__main__":
    main()