Perl has a feature where barewords preceeded by a minus need not be quoted. This allows people to do function -optiona -optionb;.

>perl -wle "print abc;"
Unquoted string "abc" may clash with future reserved word at -e line 1
+.
Name "main::abc" used only once: possible typo at -e line 1.
print() on unopened filehandle abc at -e line 1.

>perl -wle "print -abc;"
-abc
[download]

When your v-string gets packed into something which starts with a letter, you see this autoquoting in effect.

>perl -wle "print -90.0.0.1"
-Z^@^@^A

>perl -wle "print -91.0.0.1"
Argument "[\0\0^A" isn't numeric in negation (-) at -e line 1.
0
[download]

Apparently, it didn't occured to the implementors of these features to test them used together. What you are expecting from the negation of a string?

Update: If you want to work with 90.0.0.1 as a number, unpack it.

$uint32_ip = unpack 'N', 90.0.0.1;
[download]

Once unpacked, you'll be able to manipulate it using numerical operators (including -, <<, >>, ^, | and &).

Update: Better yet, use one of the existing modules (such as Net::IP or NetAddr::IP).

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