Pass a variable into a config file before uploading with file provisioner

I have a SQL unattended config file which I would like to pass in a variable before that file is uploaded using the file provisioner.
SQLSYSADMINACCOUNTS="${usr}" "Administrator" "NT AUTHORITY\SYSTEM" "BUILTIN\Administrators"

How do I go about passing in a variable to replace the ${usr} ?

thanks, not sure what you’re pointing out specifically. perhaps I should have mentioned this is a Windows machine

I don’t think that would make a difference, you still use the environment_vars to pass the env variable you want to the script or run command to replace the $x into the value.

it isn’t a script in this case, it’s just a config.ini file which has a load of settings that are passed to the SQL Server installation for unattended install. I don’t think if I placed an environment variable in the config.ini it would be picked up and changed into a literal value