/usr/bin/plog is in ppp 2.4.7-2+2ubuntu1.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 | #!/bin/sh
if [ -s /var/log/ppp.log ]; then
exec tail "$@" /var/log/ppp.log
else
exec tail "$@" /var/log/syslog | grep ' \(pppd\|chat\)\['
fi
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