I'm really not happy with the use of backticks here (at least without sanity checks).
Consider if ipnum looks like this:

192.168.0.1
192.168.0.2 ; rm -rf /
192.168.0.3
[download]

Running with -T gives :

[nobody@archaia scratch]$ ./wibble
Insecure dependency in `` while running with -T switch at ./wibble lin
+e 16.
[download]

Of course, if ipnum can be trusted, then this isn't an issue.