On Wed, Aug 14, 2019 at 9:50 AM Rolf Eike Beer <e...@emlix.com> wrote: > Hi all, > > I have discovered some problems with examples/udhcp/simple.script. I know, > it's an example, and a simplified one. Most people will still just use it > because it works, so I would like to point out at least some things. > > First, it does not really use ip. At least not if "command" does not exist.
"command" is a mandatory shell builtin. https://pubs.opengroup.org/onlinepubs/9699919799/utilities/command.html https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html section "Command Search and Execution" specifically mentions it. The reason for this mention is that its function can not reasonably be implemented as a separate external tool, since external tools don't know what functions are defined in current shell's invocation, thus "command FUNCNAME" won't work. Since it's an internal builtin, using it should be a fastest way to test whether "ip" can be executed, without assuming a path ("test -x /usr/bin/ip") or forking a possibly external tool ("which ip"). Which shell do you use so that you don't have "command"? > Fair enough, I know I have ip, so I just deleted the checks and the ifconfig > lines. > > This makes it do nothing. As I found out the culprit is this: > > if command -v ip >/dev/null; then > ip addr flush dev $interface > else > ifconfig $interface 0.0.0.0 > fi > > The difference between both cases is: ifconfig brings up the interface, ip > with this command does not. So if you are using ip this will just send DHCP > request to a network interface that has link down, which will not get you > anywhere. Yes, this is different. How about: echo "Clearing IP addresses on $interface, upping it" if command -v ip >/dev/null; then ip addr flush dev $interface ip link set dev $interface up else ifconfig $interface 0.0.0.0 fi _______________________________________________ busybox mailing list busybox@busybox.net http://lists.busybox.net/mailman/listinfo/busybox