Some issues in examples/udhcp/simple.script
vda.linux at googlemail.com
Thu Sep 5 12:57:15 UTC 2019
On Wed, Aug 14, 2019 at 9:50 AM Rolf Eike Beer <eb at 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.
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"
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 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
> 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
> ifconfig $interface 0.0.0.0
> 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
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
ifconfig $interface 0.0.0.0
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