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>>{s.strip,len}
>>Return string after removing starting 'len' characters. Parameter 'len' c=
an be positive integer or pseudo-variable holding a positive integer.

I tried to use pvar holding len but got an error:
Jul 11 14:51:37 localhost /usr/sbin/kamailio[16905]: ERROR: pv
[pv_trans.c:434]: select cannot get p1
Jul 11 14:51:37 localhost /usr/sbin/kamailio[16905]: ERROR: <core>
[lvalue.c:351]: non existing right pvar

This is part of my config file:
=A0 =A0 =A0 =A0 $avp(varname) =3D '1'; =A0 =A0 =A0 =A0 =A0 =A0<---- pseudo =
variable holding
a positive integer
=A0 =A0 =A0 =A0 $avp(result) =3D $(fU{s.strip,$avp(varname)}); =A0 =A0 =A0 =
=A0 =A0 =A0<---- s.strip

How can i =A0use variables with transformation ?