Lenght string

I need to get length of string in attribute. I found something here: https://networkradius.com/doc/3.0.10/unlang/xlat_length.html I've tried: Tmp-Integer-0 := %{#control:Tmp-String-0} Tmp-Integer-0 := %{#:control:Tmp-String-0} ... but nothing happened: /etc/raddb//policy.d/dhcp_opt82[299]: Unknown or invalid value "%{#control:Tmp-String-0}" for attribute Tmp-Integer-0 /etc/raddb//policy.d/dhcp_opt82[299]: Unknown or invalid value "%{#:control:Tmp-String-0}" for attribute Tmp-Integer-0 How to do it right?