According to I/O Operators, your use of <...> seems to be, if not deprecated, at the very least, not recommended.

unlink glob "$dir\\$ip_address.*";

would appear to be the way to go - see glob (which apparently, uses File::Glob - as suggested by kyle) & unlink.

Update:

Many thanx to FunkyMonk - for both pointing out the broken link and suggesting a fix ... link to I/O operators mended