Get interface name

Good afternoon,

I have a problem, I am currently using pppoe server to authenticate my clients, however now I implement a single user for all clients named for example “escor”, however I have a php api to see the traffic of each pppoe user however Now, as it is only one in the interface, it shows an example , , ,
and I don’t know how to get the interface to see its traffic, I was thinking of getting it through the mac in the /ppp/active section, but I can’t get the name of the interface that is in /ppp/interface

I hope you can help me to solve this problem that I have, I would greatly appreciate it.