Make /etc/network/if-up.d/dad POSIX complaint

Package Information

• Package name: busybox-ifupdown (/etc/network/if-up.d/dad)
• Package version: 1.36.1
• Alpine version: 3.19.1
• Alpine architecture: x86_64

Summary

The script: /etc/network/if-up.d/dad is not POSIX complaint. When replacing /bin/sh -> /bin/busybox with /bin/sh -> /usr/bin/dash, the following error message is shown when booting the system:

/etc/network/if-up.d/dad: 11: arithmetic expression: expecting primary: " counter-- " 

I didn't test this yet, but maybe the following could do the trick:

#!/bin/sh

# Block ifup until DAD completion
# Copyright (c) 2016-2018 Kaarle Ritvanen

has_flag() {
        ip address show dev "$IFACE" up | grep -q " $1 "
}

counter=100
while [ "$counter" -gt 0 ] &&
        has_flag tentative &&
        ! has_flag dadfailed; do
        sleep 0.2
        counter=$((counter - 1))
done

Steps to reproduce

• Install dash: apk add dash
• Link sh to dash: ln -sfn /usr/bin/dash /bin/sh
• Reboot the system