You might be thinking of the exec command. Take a look at system. It actually forks off the system call, and then the parent waits for the child to exit before proceeding. When pppd exits, the parent process will print the error message, hit the end of the loop, and repeat.

With your original question, I would do something like: my $ifconfig_data = `/sbin/ifconfig ppp0`; and then use a regexp to look for a valid IP address or whatever you like.