Given the fact that $ip holds a valid IP-Address:

my @parts=split('\.',$ip);
my $ipint=$parts[0]*256**3+$parts[1]*256**2+$parts[2]*256+$parts[3];
undef @parts;
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There might be trickier ways but that should do for the start :)

Update: Of course the MSB is in the first digit, it came to my mind when traveling home yesterday, sorry.... Thanks, jink. Well thought :)
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use signature; signature(" So long\nAlfie");