Get and set my ipv6 - strato.com

[freprec]

Hi everyone,

I am trying to get my machine to make the DynDNS service of strato.com assign an IPv6 address (only) to it.

I created a config:

allow-ipv6 = true

provider strato.com {
        checkip-command = "/etc/checkip.sh"
        username        = "domain.tld"
        password        = "my_pw"
        hostname        = "sub.domain.tld"
}

The shell script does this:
ip -6 addr list scope global $device | grep -v " fd" | sed -n 's/.*inet6 \([0-9a-f:]\+\).*/\1/p' | head -n 1

and it works as expected when executed:

# ./checkip.sh
2001:abc:def1:8f00:21e:2ff:fe12:345e

But whether I use the shell script or paste the command directly in the checkip-command in the config, the result is the same:

inadyn[1]: Resolving hostname sub.domain.tld => IP# 12.234.45.123
inadyn[1]: Get address for default@strato.com
inadyn[1]: Starting command to get my public IP#: INADYN_PROVIDER="default@strato.com" INADYN_USER="domain.tld" /etc/checkip.sh
inadyn[1]: Error running 'INADYN_PROVIDER="default@strato.com" INADYN_USER="domain.tld" /etc/checkip.sh': 0 bytes read
inadyn[1]: Checking for IP# change, connecting to checkip.dyndns.com([158.101.44.242]:80)

And then the IPv4 address is assigned again instead of the IPv6 address.

What am I doing wrong? I'd appreciate it if someone knows a solution to this. :) Thanks for reading!

Best regards

[freprec]

I found some solution, I guess.
After trying so much other stuff for hours, I noticed that when executing the command directly without shell script it seemed to miss some characters in the inadyn output.
Seems like I should have added more escape characters like this:
checkip-command = "ip -6 addr list scope global $device | grep -v \" fd\" | sed -n 's/.*inet6 \\([0-9a-f:]\\+\\).*/\\1/p' | head -n 1"

BUT it still won't work with the docker container, only with a native instance. The command looks ok:

inadyn[1]: Starting command to get my public IP#: INADYN_PROVIDER="default@strato.com" INADYN_USER="user" ip -6 addr list scope global $device | grep -v " fd" | sed -n 's/.*inet6 \([0-9a-f:]\+\).*/\1/p' | head -n 1
inadyn[1]: Error running 'INADYN_PROVIDER="default@strato.com" INADYN_USER="user" ip -6 addr list scope global $device | grep -v " fd" | sed -n 's/.*inet6 \([0-9a-f:]\+\).*/\1/p' | head -n 1': 0 bytes read